The Long And Cautious Road To The Sky

There is an old saying that if you wish to make a small fortune in aviation, start with a large one. Aviation is littered with dreams that have turned into expensive and demoralizing nightmares. Many of the concepts made sense aerodynamically while others would have filled a market need and yet still did not succeed. This axiom holds true even for the current electric air taxi push. Even with the immense amounts of money being poured into this venture, that is no guarantee that it will flourish. With so many new variables at play, a conservative approach to goals will serve to help reduce the risk of failure. Here are a few aviation ventures that suffered delays, redesigns, bankruptcies and buyouts despite optimism, sound designs and in some cases, very high valuations.


Dr. Paul Moller has worked on perfecting a vertical takeoff and landing vehicle named the Skycar for five decades. Intended to lift off from ones driveway, it was expected to be able to fly in excess of 300mph at altitudes above 30,000 feet using renewable ethanol as fuel. In 2003 it finally achieved tethered hovering flight.


Moller Skycar in a tethered hover.

To date his company has spent in excess of $100,000,000 and despite many studies, patents and tests, the design has not progressed to even a pre-production phase. Part of this is due to the amount of capital required to move to the next stage of development. Despite the design’s fit with the current air taxi craze, future investments are unlikely due to the company’s long string of excessive delays and lack of progress.


Dr. Paul Moller and aircraft he designed, (left to right) Neuera 200, Skycar M400 and Skycar M400X.



Eclipse 500/550

Eclipse Aviation was founded by former Symantec CEO Vern Raburn. His vision was a major part of a larger movement to create low-cost private jets that thousands of people would be able own and operate.


Eclipse 500 aircraft in the colors of the defunct DayJet air taxi service.

The company touted several radical new construction techniques and features that would reduce the production cost of their Eclipse 500. Development was initially rapid until a significant problem with the new engines came to light. Without these specific engines, the aircraft would not meet its performance guarantees. Other issues with contractors, controversy surrounding FAA certification and financial issues led to bankruptcy in 2008, less than a year after delivering their first aircraft. It is the biggest financial failure in the entire history of general aviation. The company’s assets have since been acquired by several successive organizations that continue to construct and support the improved Eclipse 550 aircraft.

AW609 Tiltrotor


The Bell/Agusta (now AgustaWestland) 609 is a civilian answer to the military V-22 aircraft. As a tiltrotor, it featured the vertical takeoff and landing capability of a helicopter while retaining the speed of a conventional airplane. With the program beginning in 1996, testing and development proceeded at a cautious rate leading to a first flight in 2003.


AW609 demonstrating its vertical takeoff and landing capability.

In the interim, the prototypes have continued flight testing and building the flight hours necessary to achieve FAA certification. Due to the craft’s unique nature, FAA certification categories had to be modified and in some cases rewritten, adding to the delays. An additional setback was the inflight disintegration of the second prototype resulting in the loss of both test pilots in 2015. The accident was attributed to the flight control software amplifying pilot control inputs beyond safe limits during a high-speed test dive.


AW609 in horizontal flight mode.


Icon A5

Icon Aircraft was founded in 2006 with the intent of building light-sport aircraft that would appeal to the general public.


Icon A5 in flight.

Two years after its founding, the company had a prototype recreational amphibian in the air. However, the realities of production and certification delayed the rollout of the first production model until 2014. The first delivery to a customer was in 2015 followed by an extensive pause while they redesigned their production facilities and methods.


New Icon production facility in Vacaville, CA.

They are currently building aircraft at a rate less than a quarter of what was anticipated.


Optimism And Aerodynamics

I could list dozens of other civilian projects including the VisionAire Vantage, Adam 700, Piper Altaire, Diamond D-Jet, Aerion SBJ, LearFan, QSST, and Carter PAV. But that would amount to belaboring the obvious. By now, we were supposed to have access to supersonic business jets, personal air vehicles that fly themselves and private jets that cost a tenth of what some current models do. But despite very intelligent people working on the problem and literally billions of dollars invested, none of that has panned out as planned. There is nothing wrong with optimism, but history has shown aviation startups that hope and motivation must be balanced with data and demand.

All flying vehicles consume fuel and money, sometimes not in that order. The very nature of being suspended delicately in the third dimension demand a level of redundancy and safety that is not required while traveling on the ground. If your car has a problem you can simply coast to the side the road and wait for assistance. If your aircraft has a problem you have no choice but to get back on the ground. How soon and in what condition depends on the nature of the emergency. Designers must proceed with this sobering fact in mind at all times.

When a company announces its plans for a new product, there are significant differences between software and hardware. Rushing an application or software to market has never directly been responsible for someone’s death. In aviation, a rush to market can and has killed people with amazing predictability. In the tech world, three years is an eternity. For a flying vehicle that features several unproven methods, that same three year span is nearly childlike in its optimism.

Testing For Safety

Anyone who knows anything about science understands that you should only change one variable at a time and measure the effect. Smart aircraft designers similarly never test a new type of engine with a new type of airplane at the same time. In this situation, it appears that the designer is attempting to not only combine a new airframe and powerplant, but a new control system and new airspace integration/automation. Any single one of these challenges would be enough for a company to tackle. All of them combined may prove to be a minefield of delays. For a look at what has to be done from a purely operational standpoint, not considering any business model issues, one must consider all the constituent components of the vehicle.

This new vehicle will have a major hurdle in its hybrid electric propulsion system. While hybrid rotor systems have been proven on aircraft as far back as 1959 with the Fairey Rotodyne and more recently with the Airbus X3, electric helicopters and eVTOL vehicles are still in their infancy. This means that it will take more time and money to validate and certify an airworthy configuration since there are so many unknowns. The good news is that future aircraft that use the same type of propulsion system will not have to rewrite the rule book.


Fairey Rotodyne

Flight controls are very important for the obvious reasons. So far, all illustrations of the most talked about air taxi concepts show no conventional flight control surfaces such as elevators and ailerons. Considering that during cruise flight the vertical lift rotors will be stowed and cannot be used for attitude control, it will be interesting to see exactly how they plan to control the vehicle. Again, seeing that whatever method they take will be unconventional, prepare for extended test periods while all of the proper redundancy is built into it.

The airframe itself may seem like the easiest component to build, but there are plenty of hurdles to clear with this piece of the puzzle as well. Vibration and flutter testing, occupant safety, crashworthiness and dynamic stability are all things that must be tested before certification is issued. In addition, the retractable vertical lift rotors will most likely be considered as separate systems. Therefore, the designer must prove that a failure of any unit to retract or deploy will not cause loss of the vehicle. 


Lightning strike testing on a mockup.

It is very clear even from this relatively short list of design issues that assuming a short gestation period is not prudent. Throwing more money at a problem doesn’t always solve them. A history of being able to rapidly scale in other industries does not translate to building hundreds of flying vehicles in a few years, especially when the company has no prior experience in aviation. This is worthwhile technology that deserves the time and attention required to properly test it before rolling it out to the public.


Perhaps a lot of details are purposely being kept from the public. Maybe the propulsion systems, automation systems, flight control laws, and vehicle aerodynamics are all being tested concurrently. Maybe there’s more than what the media and general public has been shown in articles and press releases. Maybe there’s a secret squadron of prototype air taxis flying out of Edwards Air Force Base. Maybe there are special certification processes in the works that will allow fast-tracking of an entirely new class and category of aircraft. If this is the case, then all the words I have written mean absolutely nothing. If not, then we are all in for a longer wait than expected.

flight test pilot airplane aviation

Patience and precision is required at every stage of design and testing.

Perhaps the reason I’m so preoccupied with caution is because I don’t want an avoidable incident to occur where the public loses faith. Investors tend to be apprehensive about putting money into a venture when one of its test vehicles is on the news at the bottom of a smoking hole. Accidents may happen even with every precaution observed and meticulous planning. But to entice them by through optimistic blindness is inexcusable. There is no critical rush to get flying cars operational. We as humans have existed on this planet for a very long time without them. Adding a few years of development to ensure that they are released in a responsible and useful manner makes all the sense in the world.



Flying Cars: Challenges In Design And Implementation

Whenever people find out that I’m involved in aerospace research, I get asked the question “Hey what do you think about flying cars?”. Invariably, my drawn out utterance of the word “Wellllllllll” serves as a precursor to me depressing the entire group with copious servings of aerodynamic reality.

Most of the current flying car designs are from startup companies with no history or focus in full-scale aviation. This isn’t necessarily a problem as many times a novel solution is discovered by firms outside of a given industry. Several companies have went with the “Let’s scale up a quad/octo/dodecacopter and stick a person inside it” method. Some others have taken the Star Wars pod racer look and gave it a more utilitarian slant. I will admit, several of these designs look pretty awesome. But unfortunately, the laws of physics don’t respond to awesome. It appears that many of the designs were made without consideration of aerodynamics, human factors, the atmosphere or the realities of being in a small flying vehicle.

Established aerospace companies such as Boeing, Cessna and Bell should theoretically be all over the flying car craze. Bell, as a large helicopter manufacturer is well versed in the techniques associated with vertical takeoff and landing. Cessna not only makes some of the fastest business jets available, but they are responsible for the best selling light aircraft type in history, the Cessna 172 Skyhawk. And as if you didn’t know, Boeing dominates the US commercial aircraft industry.

So far Bell has teamed with Uber to help accelerate the technological leaps required to enable the development of point-to-point, electric VTOL vehicles. This doesn’t mean they’re working on a prototype, it just means they’re helping guide a company that has little to no experience with anything that flies. Boeing for their part has had a few limited projects in the past to design flying cars but were canceled before ever getting to a flying prototype. Finally Cessna is not involved at all with any type of flying car construction or collaboration (at least not publicly).

What could be some of the reasons for wide-eyed startups to be chomping at the bit to build these vehicles while grizzled industry veterans keep a wary distance? Could it be that they’ve seen some things that the new companies haven’t yet? Do Bell, Boeing and Cessna have the thousand-regulation stare? In this piece, I’ll highlight some of the issues facing flying car designers and why it will probably take a lot longer than the public thinks to make them a safe and widespread mode of travel (notice I didn’t say impossible…just a longer wait).


There is a misconception today amongst the non-aviation public that all modern airplanes are flown by computers and the pilots just sit there eating chocolate cake and watching Top Gun on their tablets. The reality is that pilots still fly the airplane, there’s just a computer that stands as a gatekeeper to ensure that the aircraft stays within limitations. Even still there are regions of flight where human skill is faster and more accurate than the computers. Autopilots/FMS still have to have flight plans loaded in advance and these plans invariably change multiple times per flight. Pilots still monitor and adjust systems during flight. They regularly deal with failed systems, changing weather conditions, rerouting by ATC and a multitude of other tasks. The automation is there to help the pilots focus on things that the automation can’t do.

Yet when reading articles on flying cars, the answer to everything seems to be automation. How will these flying cars operate in congested cities with skyscrapers all around them? Automation. How will the vehicle transition from vertical to horizontal flight? Automation. What will happen if an engine fails or a blade gets thrown? Automation. No detailed discussion of thrust vectoring or ducted fans or control surfaces. No mentioning if the omnipotent automation will activate systems via pushrods, cables, hydraulics or electric servos. Just automation. This shows a disconnect with actual flying vehicle design and a mere concept.

In order for automation to work, it needs something to work with. And once it has something to work with, it has to know the static and dynamic stability margins for the vehicle to ensure it remains flyable (better hope the occupants understand weight and balance). It also has to know where all other vehicles are. And all obstructions. And all restricted airspace. And considering that the passenger-not-pilot won’t have any control, the automation also has to identify and handle any conceivable emergency situations. Given the amount of effort being put into self-driving cars that only operate in 2 dimensions, a 3 dimensional activity like flying will require automation that is going to be unlike anything ever coded.


A few questions about how this system will integrate with the National Airspace System are probably in order: Will this system work with the upcoming ADS-B mandate in 2020 that most aircraft in the United States will have to conform to? Will there be an international standard to allow sales in other countries? Will the system communicate to local air traffic control? What about operations near airports? Will flying cars be banned within X miles of a runway, or will they be allowed to funnel into the airport parking lot via strictly monitored ingress routes? Will air traffic control need to monitor and separate commercial, private and military traffic from flying cars? What about military training routes? What about prohibited areas? How will flying cars integrate with news and medivac helicopters? What about sightseeing…at some point people are going to want to see the Grand Canyon, Niagara Falls and Yosemite from their own flying car. Will people on the ground have to hear the constant drone of, well, drones? What about Washington D.C.? The entire nation’s capital has a permanent TFR which, short of some landmark change in legislation would rule out any flying cars within its vast boundaries. The same issue arises at football and baseball games since they too are ensconced in TFRs during games. In all honesty, even if every technical issue is surmounted, just figuring out integration and getting FAA approval for the plan is going to take the wind out of the sails of all but the hardiest of companies.


So far most of the animations show the flying cars operating in clear skies or silhouetted against a fiery sunset. While it looks really nice, it is not the full story of where these vehicles are going to be operated. They have to consider that people are going to expect that they can jump in their flying car and head home even if it starts raining, snowing or blowing 30mph out of the northwest. Are these vehicles going to be certified for known ice? The fact that even the largest commercial airliners have to be serviced with de-icing fluid before takeoff demonstrates the seriousness of the threat. After takeoff, hot bleed air from their jet engines can be routed along the leading edge of the wing to melt ice off. Just as critical is the engine anti-ice (different than de-ice) system that keeps ice from collecting on the nacelle lip. Needless to say, a chunk of ice down the inlet of a jet engine spinning at several thousand RPM is not an ideal situation so they take steps to prevent it from happening in the first place.

Now imagine a small flying car with uninformed passengers riding in it on a cold night. They have no knowledge of the environment in which they’re in, no ability to affect the flight and no way to save themselves other than perhaps a land-now button or a ballistic recovery parachute. A flying car encountering ice will rapidly collect it on the windshield, flying surfaces and engine nacelles, robbing the rotors of thrust, disrupting smooth airflow over the wings and weighing the aircraft down. Since these aircraft are intended to be electric, its only means of protection is to draw a lot of current to heat the critical surfaces, or carry the extra weight of a fluid known as TKS that is pumped out of tiny holes to retard ice accumulation.

There are other weather threats besides ice. Most of the designs presented are not touting the use of aviation aluminum as the primary construction material. Thus we can assume that a composite such as carbon fiber will be used instead. While very strong for its weight, carbon fiber does not react well with electricity. In the event of lightning striking a flying car…and it will happen…the manufacturers must prove that no strike will damage the structure beyond airworthiness limits and just as importantly, that it will not disable any of the automatic flight systems. Exhaustive testing and shielding will be required before any design is certified. Some existing aircraft use lighting diverter bars on composite parts to give the current a path to follow. It is then able to follow these routes and discharge through static wicks rather than blow holes in structure. All parts of the airplane must have a conductive path to these wicks in order for them to function properly. Again these are the realities of the atmosphere in which we fly and why airplanes cost so much to design.

Passenger Comfort

I make it a point to ask people who have mentioned wanting to have a flying car if they have ever flown in a small plane before. The answer is invariably “No.” This is very telling as the fantasy of flight is sometimes more attractive than the reality. However, most of those same people have flown in commercial aircraft before and remember experiencing turbulence of some kind.

Turbulence can range from gentle rocking to quite literally bouncing people off the ceiling. Mind you, these are heavy aircraft with high wing loadings. They have a lot of inertia and they can still be thrown around like ragdolls in the right conditions. Small aircraft by obvious virtue of being lighter are affected to a greater degree than large aircraft. Imagine the effect of 5 foot waves on a cruise ship and then picture an inflatable raft in the same size waves and you get an idea of the large plane vs small plane dilemma.

I have personally been bounced around rather brusquely in small aircraft before. Friends of mine have hit their heads on the ceilings while wearing their seatbelt due to the severity of turbulence they’ve encountered. Since flying cars are going to be lighter than many general aviation aircraft, this does not bode well for the dyspeptic among travelers. Hot air, strong winds, wind tunnel effects near skyscrapers, outflow from rain showers, and even the wake from other vehicles can all be nauseating for the uninitiated. While manufacturers will probably try to say that computerized flight controls will smooth out the bumps, that’s going to be limited by the vehicle’s lack of inertia. All I can say is these flying cars better have a really good air conditioning system and a place to store used barf bags.

Preflight and General Safety

Before any aircraft takes to the sky, the flightcrew will perform a preflight inspection commonly referred to as a walkaround. This activity is standard for every airplane from Piper Cub all the way up to Airbus A380s. During this inspection, they are looking over the condition of the aircraft, verifying fluid levels and quantities and ensuring that there are no blatantly obvious deformations. So far, flying car concepts have intimated that a user just hops in, pushes a few buttons and flies away. While it may seem like a yeah-so-what detail, this has very important ramifications for who will actually have their butts in these machines. Are the sensors that detect buildings and other aircraft obscured by dirt or dead insects? Are the thrust vectoring vanes able to move freely? Did some idiot ram a shopping cart into my rear stabilizer?

Since a person can’t just pull over if there’s a problem, and more critically, there may not be time to land or deploy a parachute if certain items fail, inspecting a flying car before flight will be just as important as it is for real aircraft. This will require teaching non-pilots the importance of ensuring the airworthiness of their vehicle before every flight. Somehow I have a feeling that there will be a lot of lip service paid but very little attention. The allure of jumping in and flying away is just too strong.

As for general safety, some designs have serious issues with the placement of certain components. For example, when I see a 2 seat quadcopter with unprotected blades, I see a lawsuit because someone walked into a running rotor and was disfigured or killed. Therefore, regardless of the number or orientation of the blades, they would have to be recessed into ducts in order to keep people from getting maimed when entering, exiting or walking around the aircraft. This would also protect the blades from damage in the event of a bird strike (assuming none got sucked down into the duct) and allow for thrust vectoring without tilting the entire motor/rotor combination.

There should be a battery firewall feature since the risk of thermal runaway while remote, is still a possibility. Someone once suggested to me that the offending battery be jettisonable. I then mentioned that the people below who get crushed/burned by a 500lb lithium ion battery falling out of the sky would be pretty upset if they survived and he agreed the idea wouldn’t be socially acceptable.

Likewise, a land-now feature and ballistic recovery parachutes should be standard. If a passenger is not going to be allowed to be a pilot, they should at least have a way to save their own life if an emergency develops. With that in mind, occupant enclosures should have sufficient bracing and structural integrity to protect people in the event of a rollover or hard landing.

Building a flying car to a reduced power level is another good idea to help in the event of an engine failure (assuming multiple engines). Setting MTOW to correlate to 80% of total engine thrust gives the vehicle a margin in case of engine failure. If a powerplant takes an early retirement, the remaining engines can be brought up to 100%. This should be enough to help balance the reduction in power and prevent airborne rollover from the sudden loss of thrust in a given quadrant.

So those are some of the off-the-top-of-my-head observations about flying car design (we didn’t even bother talking about the motors and the energy density of chemical fuels versus batteries as that’s enough for another article). Mind you, these are considerations that anyone who builds an aircraft must incorporate into their design before cutting metal. Some people will complain and say “Well if you know so much why don’t you build one!”. To which I’ll respond “How do you know I’m not?”

In any case, I write this because I love aviation. I grew up involved in aviation and what I see is a collision course of people who have great imaginations and some wonderful ideas, but not enough grounding (punintentional) to know why some of those ideas are not wonderful. If flying cars are going to be commonplace and accepted, they have to be built right. People are not going to tolerate these things taking them to the wrong destinations, to say nothing of what would happen if they start falling out of the sky due to underestimating the laws of aerodynamics.

Uncertainty Of Weather

Yesterday was forecast to be a very violent day in north Texas with regard to weather. The setup yesterday was the equivalent of a warehouse filled with gasoline, dynamite and aluminum powder. All the atmosphere needed was someone to drop a match and the whole works would have went up. The forecasts recognized this hazard and warned people accordingly. For a variety of reasons, the explosion never occurred and the majority of, but not all residents in north central Texas escaped with no damage. And I can accurately forecast today that there will be many who question the emphasis on danger yesterday, that the meteorologists hyped up the situation and that they don’t know how to predict weather.

All day the local stations had their meteorologists going over the situation and reminding people to be vigilant. Even the Storm Prediction Center opted to raise the alert level from enhanced to moderate, signifying that the conditions were right for explosive growth of violent storms. Needless to say, things became very tense as the day wore on. People began covering their cars with cardboard and mattresses, schools cancelled sports and some companies let people go home early. But as the first cumulonimbus towers started going up, the forecast changed. Instead of being ahead of the dryline, they went up behind it. This had a significant effect downrange on storm intensity.

In addition to that, the inversion cap was stronger than expected. This prevented the growth of storms to the extent that had been expected. In effect, much of the stored energy in the atmosphere was not available to be used to power the storms. There were a few discrete supercells that sprang up ahead of the front but not in the number or coverage that was expected. Some areas west and north of DFW did experience significant damage and a few storms became tornado warned but overall the widespread catastrophe never materialized.

Why are people upset?

To be honest, there are valid instances of media overhyping garden-variety snowstorms or treating a couple inches of rain over several days as a deluge. In my personal opinion, the overhyping of relatively benign types of weather is damaging to public confidence in forecasting and weather services in general. On the other hand, when there is a situation where violent thunderstorms are likely, there is a duty to remind people that failure to pay attention may cost them their lives.

Part of the confusion is that the severe forecasts had been in the news for about a week prior to the event. Forecasts that far out are based off of computer models of the atmosphere. The models take the current weather and interpolate possible scenarios for the future. As it gets closer to the actual forecast day, the models are refined with more up-to-date information, for instance did a upper level disturbance move the predicted 400 miles or did it actually move 450? Within 24 hours of an event, the importance of real-time atmospheric soundings and measurements for a given region becomes more important as meteorologists combine those readings with the models and their own knowledge to create a picture of what may happen.

Faced with this situation, forecasters have to make constant observations and continually update their prognosis. There are no models that can tell exactly where and when a storm is going to strike. It remains the province of humans both in weather centers and on the ground near the storms to make the final determinations. When the atmosphere is literally on the edge, it would be irresponsible to play down the significance. If even one person was killed by a falling tree or flying debris, every meteorologist would be skewered for not providing enough warning. The other extreme would be advising everyone to take shelter at the sight of a single cloud, resulting in public apathy and indifference.

The only solution is finding a balance between too little and too much information. People who grew up in Tornado Alley understand that for at least a couple months out of the year, the atmosphere conspires to ruin your life and treat it with the proper attention and respect. However, the recent influx of people from other states to the Dallas/Fort Worth area means that there are many people who do not understand that spring thunderstorms here are not like storms in any other part of the country. They are massive living things with nasty attitudes, both beautiful and sobering to see in person. A single storm can cover the better part of an entire county and tower twice the height of Mount Everest (for comparison, next time you ride an airliner, look out the window and imagine being twice as high). These storms do not take being ignored very well and lifetime residents understand this. It’s a situation where as cliché as it sounds, being safe is better than being sorry.

(My best friend who lives in New York got a rude introduction to Tornado Alley weather. When he arrived in Dallas for airline pilot training several years ago, he got to witness an EF-2 and car windows being shattered by golf-ball hail. It redefined his idea of a severe storm and made it impossible for him to watch Twister without laughing at the inaccuracies.)

Another aspect is misunderstanding the capabilities of weather prediction methods. We trust so much in technology that any uncertainty is met with fear and anger. “Why don’t you know if there’s going to be a tornado? Don’t you guys get paid enough? Why can’t you use your radars?” There is a limit to our abilities and short of meteorologists being pyschics, they cannot predict with street-by-street accuracy. There are quite literally millions of cubic miles of atmosphere that are in constant motion. Even a computer model that has 1 cubic mile resolution has a lot of uncertainty and needs to be qualified by other data that may or may not be available at a given time.

We also cannot discount the “pass-the-exam” attitude that has started to creep into society. Instead of understanding a concept, students will say to a teacher “Just tell us what’s going to be on the exam”, thus defeating the purpose of sitting in class and learning in the first place. With weather, many people don’t know or care about the lifted index, think that CAPE is something that a superhero wears and only want to know “Is it going to rain in my town?” A look at any meteorologist’s Facebook feed is evidence of this. Of the hundreds of questions being asked, a large portion of them are “Is it going to affect my town?” This behavior is understandable as people want to know if they should take action to protect themselves, but it also shows a lack of understanding of the massive scale on which weather systems operate (the same system that “didn’t happen” for north Texas spawned tornadoes in Oklahoma).

Finally, the emotional rollercoaster of imagining your home being destroyed, wondering how to protect your family and then being told “Nah, not today” can take its toll on anyone. The urge to lash out at the people responsible for your mental torture is understandable. However, there really is nobody to blame. The atmosphere is going to do what it’s going to do. All we can do as humans is pay attention and have a plan in case things get bad.

In conclusion, there are situations where media makes a big deal out of nothing. In fact with most severe storm situations, there literally is nothing until around 3pm. But there is a huge difference between naming a snowstorm that dumps a couple inches of powder versus telling people there’s a good chance that softball-sized blocks of ice are going to crash through your ceiling. There’s a difference between delayed school opening due to flurries versus finding a new school because the old one was shredded by a 200mph vortex. Alerts used properly are useful. Alerts that are used for anything other than blue skies has a detrimental effect on the public’s perception of weather forecasting and is something that must constantly be considered by producers of news programs.

Individuals must also take responsibility for their own knowledge about weather. Understand the difference between a watch and warning. Know basic cloud structures and what they mean about the atmosphere. Realize that a forecast can be absolutely accurate even if you personally experience the complete opposite. And most importantly remember that meteorologists are humans who are doing their best to decipher what the weather is going to do.

What Happens When The Engine Quits

I’m still sticking to the idea of writing shorter articles with more plain language rather than my usual 4 to 5 page descriptions of obscure aerodynamic theories. I know, I skipped the month of July…it happens when you’re as forgetful as I.

Think we can make the runway from here?

Comedian Mitch Hedburg had a joke that escalators never break, they can only become stairs. The same holds true for airplanes that lose an engine, they simply become gliders.

A lot of movies show what happens to an airplane when the engine fails. With very few exceptions, they’re all wrong. Hollywood tends to overdramatize some parts of aviation and underdramatize others. Airplanes do not plummet from the sky, the controls don’t lock up and pilots don’t ask ATC to tell their wife that he loves her (insert multiple alimony payment joke here).

Aircraft are designed to fly, not to fall. Air moving over the wings provides lift which keeps the airplane in the air. Since air isn’t going to move itself, something has to push the airplane fast enough for lift to be effective. That’s the job of the engine. By creating thrust, the airplane is able to move forward, generate lift and do that thing we like to call flying.

But say for example that the worst luck has occurred and the engine decides to take an early retirement. Now what happens to our airplane? The answer is very simple…it glides. Needless to say, the glide characteristics of airplanes are as varied as their shapes, but all airplanes from the smallest private plane to the largest commercial airliners will glide. Whether or not they glide to an airport depends on a few things.

In physics, there are two energy states that are important to a gliding airplane. You have kinetic energy and potential energy. Kinetic simply means energy stored due to speed. This is the force that causes injury in car accidents…the faster you go, the more it hurts when you stop suddenly. There is also potential energy, which is the energy that can be created by allowing an object to fall. For this state, the higher you are, the more it hurts when you stop suddenly (picture a bellyflop from a 3 foot diving board vs a 30 foot diving board).

If an airplane has at least one of these states with a high value, it will be able to glide somewhere without an engine. If it has both of these states fully charged up, it can really glide somewhere. If by chance it is low on both states, the gliding range will be very poor and in some cases, nil. The Air France Concorde accident is an example of what happens when airspeed is still relatively low and there is no altitude to trade for velocity. The Air Canada “Gimli Glider” 767 incident shows what happens when you have airspeed and altitude in your pocket, plus pilots who know how to manage energy.

For decades, the Space Shuttle was the world’s fastest and heaviest glider. Returning from space at 25 times the speed of sound, it would make a powerless landing at just over 200mph. It goes without saying that Shuttle pilots were well trained in managing energy, and had tons of potential and kinetic energy to work with. For practice, they would go up in modified Gulfstream II business jets, reverse the engines and do approach after approach at the same angles and rates that they’d experience in the final stages of a Shuttle landing.

When pilots don’t know how to manage energy, the results are sadly predictable. Pinnacle Airlines 3701 experienced an double engine failure at high altitude. From 41,000 feet, the CRJ200 aircraft could have easily glided 50 miles or more in any direction and landed at one of several adequate fields. But the pilots focused so much on restarting the engines that they ran out of altitude (potential), airspeed (kinetic) and ideas at the same time. The result was the loss of both pilots and the airplane.

As for how airplanes fly without power, just pay attention on landing. Every airplane touches down at or near idle power. Many commercial jets go to idle around 50 feet, while smaller general aviation aircraft might be at idle power for the entire approach (a notable exception is any Navy aircraft, as they go to takeoff power the second they hit the deck just in case the hook misses the wires). You’ll notice that the airplane doesn’t shake, the controls don’t vibrate, and you don’t just drop straight down to the ground. Airshow pilot Bob Hoover used to shut off both engines in his Shrike Commander twin and THEN go into a big looping barrel roll just to show how managing energy works when you know what you’re doing.

So now you know what really goes on the next time you see a movie with an airplane emergency. Not to say that engine failures don’t cause the pilot’s heartrate, breathing rate and sweatrate to increase, but it is not always the wrestle-the-controls-call-control-tower-I-love-my-wife-and-kids-and-goldfish situation that it’s portrayed to be.

It’s Wi-fi, Not Wi-Fly

For the record, I’m not an IT specialist, a security analyst or a person with top secret clearance (my clearance is bottom secret only). I am however someone with a fairly extensive knowledge of aircraft, systems, avionics and other stuff that’s related to being off the ground at high speeds. Therefore, I’m going to address the aircraft systems side of the current wi-fi hacking issue.

Recent articles have stated that it is possible to hack into an aircraft’s controls via a wi-fi connection. Some hackers have even publicly stated that they could and have get into an airplane’s avionics (and they probably got a nice visit from gentlemen driving cars with government plates soon thereafter). The worst case scenario that keeps getting bandied about is a passenger taking over the airplane from a laptop and making it go wherever the hell they want. This may be possible on some astronomically small level, but in reality it is not very plausible with current aircraft designs.

Everyone always talks about how airplanes are flown by computers. I’ve been at airshows where people next to me confidently tell whoever will listen that “Those Blue Angel pilots aren’t even doing anything. The computers are flying the airplanes, it’s all a program.” Passengers often assume that the pilots up front are just following commands from “ground control” and that computers will be able to take over completely by 2017. This is what happens when an industry touts its technology rather than its technicians…the machines become the heroes.

Part of this is a misunderstanding of basic aircraft systems, which considering the level of knowledge most people have about aircraft in general, is not surprising. Aircraft may be “flown” by computers, but human pilots tell the computers what to do (and if the computers get a a superiority complex, the humans can override the machines). It’s the same as how computers in your car govern much of its operation, but you still turn the wheel and hit the pedals manually.

Aircraft are a weird combination of old and new technology designed to provide ease of operation, redundancy and graceful degradation. Save for a few military jets (the statically unstable F-16 as a prime example), virtually all aircraft have a physical connection from the cockpit controls to the control surfaces. This ensures that even in the event of a major emergency, the pilot(s) will be able to maneuver the aircraft to a landing. These physical connections may be steel cables, pushrods, hydraulic actuators, screwjacks or a combination thereof.

While the old technology works great for ensuring that pilots can continue to fly even after malfunctions, the new technology is perfect for making the aircraft more precise, more capable and easier to manage over a variety of situations. Of course, this all hinges on the pilots understanding and being masters of all the different modes that the automation systems offer (they do and they are). Some of these systems include:

  • Where-Are-We Systems: Inertial navigation systems (INS) are self contained units that use laser ring gyros to determine where the airplane is at any point on the planet with extreme accuracy; global positioning systems (GPS) that use satellites to triangulate the aircraft’s position. These prevent getting lost, which as a rule tends to erode passenger confidence.
  • What-Are-We-Doing Systems: Attitude Heading Reference System (AHRS) that uses accelerometers to figure out what the pitch, roll and yaw state of the aircraft is; Air Data Computers (ADC) takes analog inputs from the pitot-static system and Angle Of Attack (AOA) probes to provide the pilots and other computer systems with information on how fast and how high the airplane is.
  • Do-What-I-Tell-You Systems: Input interfaces like the Control Display Unit (CDU) allow pilots to enter data into the Flight Management System (FMS) to create and manage flight plans, and Autopilot Mode Control Panels (MCP or FCU) that give the pilots the ability to change autoflight settings or most importantly, disengage automation if the situation calls for it.
  • How Are We Feeling Systems: The Central Maintenance Computers (CMC) and crew alerting systems (EICAS) check the health of the aircraft, run checklists and alert the pilots to any unusual situations. These are the computers that stole the job of the flight engineer…the third guy in the cockpit you often see in old movies.
  • I-Can’t-Let-You-Do-That Systems: In some aircraft there are systems that prevent pilots from exceeding certain limits. Examples include Thrust Management Systems (TMS) that protect engines from overheating or overspeeding and commands the autothrottle system, and Flight Control System computers (FCS) that process information from various sources, determine what the pilots are asking for in terms of maneuvering and either direct or implement those inputs to the control surfaces and engines.

At this point you may have noticed that the aviation industry loves acronyms. You also may have noticed that there is not one single computer that controls the airplane. Probably the most important system in the bunch, the FCS is usually comprised of several computers all speaking different languages. If one computer doesn’t agree with the others, it is overruled. If two computers don’t agree with the other two, the fifth one kicks in as a tiebreaker. Needless to say, the implementation is far more complex than linking a couple desktops together with an ethernet cable, but the theory is straightforward.

Beyond just being the Supreme Court of the airplane, the FCS also acts as a mediator between the pilot’s inputs and control surface positioning. This provides protection against exceeding certain attitude limits, speeds or energy states. In some aircraft, full-time protection is provided to prevent pilots from This protection is present even if the pilots are flying the aircraft by hand. In other airplanes, protections are more limited and mostly confined to autopilot modes or dampers that reduce unwanted transients in a given axis. In any case, the idea is to prevent a pilot-induced situation from damaging the aircraft.

There is an even more advanced group of aircraft that operate with what is known as fly-by-wire. These aircraft have virtually no mechanical connections to control surfaces. They use electrical signals produced by force sensors or position transducers to trigger the movement of a self-contained hydraulic actuator near the control surface. The FCS in this case becomes the equivalent of Judge Dredd whereupon it declares “I am the law!” as it pertains to aircraft operation (seriously, the protections are referred to as Control Laws…if you flew an Airbus you’d be cracking up at that last pun). Pilots at that point are “educated suggesters” who tell the airplane what they want and the airplane decides if it’s a good idea or not. For example, if a pilot sees a giant condor while climbing at 400mph and yanks back on the controls, instead of allowing the wings to be ripped off, the FCS will say “Listen, I know that massive bird startled you, but if I let you pull as hard as you’re asking, we’re going to have bigger problems. I’m going to limit you to 1.8G rather than 5.3G. You’ll thank me.

Different manufacturers have different views on how this should be implemented. Boeing prefers a more pilot-centric interface while Airbus leans towards a computer-centric operation. Both methods have their advantages and drawbacks. As creepily cybernetic as this sounds, commercial fly-by-wire aircraft still have mechanical reversions so that in the event that all the computers decide to divide by zero, the pilots can still fly the aircraft to a safe landing.

What is the point of me writing all this aerotech babble? To try to explain that aircraft control is a complex and well thought out architecture. Most of the robustness is there for nature and emergencies. Situations like getting struck by lightning cannot affect the operation of the critical avionics, therefore aircraft are tested by literally getting zapped by a massive Tesla coil before they can be certified. The loss of an ADC cannot cause the airplane to go out of control, therefore multiple ADCs are installed. The total loss of electrical power cannot cause the airplane to shut down its fly-by-wire controls, thus a deployable ram-air turbine is installed for just such an emergency. In the face of all these natural and mechanical threats, it therefore seems overly simplistic to assume that a hacker could seize control of an airplane.

Herein lies the issue with “laptop terrorist” scenario: There is no conceivable way that an individual can seize control of an airplane through a wi-fi signal without someone up front (read: pilots) figuring it out and taking corrective action. If for some implausible reason both pilots don’t notice the change in flight path, it is guaranteed that the air traffic control center responsible for the flight would notice that an airplane under positive radar control just decided to stroll off on its own. Even if someone could find holes in a firewall and hack their way through all the different systems to get to the autopilot, controlling the aircraft is not as easy as typing “C:\>FLYTOCUBA.EXE”.

But for argument’s sake, lets say Super Hacker can figure out how to change the heading or altitude. For all intents and purposes, control of the airplane is now in the hands of some guy in seat 37Q and everyone is doomed, right? Wrong. The pilots are not helpless, nor are they at the mercy of computers, laptops or otherwise. All they have to do is pull the disconnect switch on the autopilot. In the event that Super Hacker figured out how to disable that function as well, they’ll just pull the A/P circuit breaker, then walk to the back and smash his computer over a beverage cart.

All joking aside, this threat illustrates the continued need for humans to be in the decision loop when it comes to flying commercial aircraft. The insistent push for total automation especially in the wake of the Germanwings catastrophe is an emotional reaction that ignores the advantages of having both humans and computers working together. When backlit against the threat of nefarious individuals who wish to do harm, these advantages are even more important. Nevertheless, aircraft will become increasingly more automated in coming years and protecting them against electronic threats will be just as critical as protecting them against ice and microbursts.

For now, you don’t have anything to worry about.

Flight 370

A media circus doesn’t even begin to describe the unmitigated crap festival and bazaar that is passing for coverage of Malaysian Airlines Flight 370. This is our problem in aviation: we wait until an accident or disaster to go on television and then preach about how safe aviation is and how rare these events are. Our aerospace journalists and aviation experts attempt to quell the ratings-driven lunacy being excreted from the often gorgeous and equally vapid mouths of the news readers. Little do our industry spokespeople know that these news readers are trained in the use of logic countermeasures, where anything that makes sense is spoofed into a far-fetched and much more sensational conclusion. And I’m not even going to mention those other aviation “experts” who are more interested in grinding their own personal axe than being a supportive face for a woefully fragile industry.

First and foremost, the treatment of the families was disgusting. Perhaps it was simple naiveté where the airline did not want to believe that anything bad had happened. Maybe it was a cultural inability to accept blame as we saw in the Asiana accident. In either case, they seemed overwhelmed and confused from the beginning and that is understandable. Crashes are so seldom (at least in western society and those countries that attempt to hold minimum safety standards) that there isn’t much practice in how to deal with the aftermath. But that isn’t an excuse. Once you decide you’re mature enough to operate international airliners, you’re mature enough to be honest about any accident. The first thing that should have been done after a reasonable search of perhaps 1 to 3 days would have been an admission of loss to the families. Let them start healing while you continue looking.

Lest I blame Malaysia Airlines completely for that violation of decency, let us look at the goofballs in our own American media who immediately starting developing scenarios that sounded more like the pitch for a Jerry Bruckheimer film than plausible aircraft crash scenarios. The fact that Rolls Royce continued to receive engine health data for 4 hours after last contact made everyone pull out a calculator, go on Wikipedia and multiply the 777’s cruise speed by 4. Maybe it landed in the Vietnam jungle. Maybe they defected to China. Maybe terrorists stole it and are hiding it until they use it as a ETOPS cruise missile. Maybe aliens beamed it up into the mothership. All of which amounts to grasping at straws. In not a single one of those situations did people consider that these were real people with real families who did not want, nor need to hear their plot twists.

The use of terrorism as a crutch is epidemic. Anything mysterious or not immediately explainable is labeled terrorism. But the events of 9/11 were a horrid aberration. Loss of life due to a select few maladjusted individuals with a one-in-a-billion plan will happen again, but it will not be a direct copy of what happened on that day. To automatically assume that it will is a legitimate loss of situational awareness when it comes to security and safety. As much as people would like to ignore it, there are plenty of ways for an airplane to crash that do not involve terrorism. While nefarious persons may have caused the disappearance, precious days were wasted chasing other theories that made no sense whatsoever.

When the “Terrorists are hiding the plane in Siberia” (where somehow there is enough Jet-A and deicing facilities allow it to fly across the Pacific to attack America) plots unraveled, the pilot then became a suspect. God forbid if a pilot actually likes airplanes enough to take pictures of them and have a flight simulator in his house. I guess all the people who have model train sets are bent on blowing up the entire Southern Pacific railroad. While no stone should be left unturned, the focus on the captain’s mental outlook was probably…okay it was (and I’m not accident investigator but let’s use common sense here) out of sequence. Find the airplane, then figure out if the flight crew was unstable. What good does it do to dissect his life and not have the airplane to investigate if this is true or not? To bastardize the old axiom, “Find the airplane, find the airplane, find the airplane.”

To the world’s credit, those who know how to search are trying very hard to find it. Search teams from multiple nations are combing the ocean to locate some piece of debris from Flight 370. Each lead keeps coming up empty. If there weren’t hundreds of people who were affected by this, the constant switching of search locations would almost be comical. The powerful assets being used are quite capable of detecting a missing aircraft, even sunken in thousands of feet of water. However, if the search area isn’t narrowed down logically first, these wild goose chases will continue (I wonder if any of the search organizers used John P. Craven’s method that helped locate the USS Scorpion when it too mysteriously disappeared. Like Flight 370, it too had made an unexpected turn before its destruction which complicated the search). On the positive side, the solidarity between countries that are sometimes chilled towards each other has warmed a bit, if for no other reason than working together to find the lost craft, its passengers and crew.

The insidious left turn made by the pilots was claimed to be a criminal act by people who should know better. If I kick open a person’s door and run into their house, is it a criminal act? What if I’m trying to drag them out because their attic is on fire and they didn’t answer when I called? Context makes a huge difference in actions. Without knowing what may have caused the crew to change direction, nobody can speculate on why they did. There was also a seldom mentioned rapid change in altitude, if my memory serves me correctly, a rapid climb to well over 40,000 feet followed by an equally abrupt descent to around 12,000 feet. I don’t even fly jets but there are only a few things that can cause that kind of maneuvering. In fact, there are only two things that would normally cause an immediate reversal (or partial reversal) of course in a jet that is quite capable of flying for 3 hours on a single engine


1. Fire: Fire is a no-brainer. If a fire starts on an aircraft, chances are it can be extinguished by the on-board systems. If it can’t, or if it continues to smolder, then there is a very serious problem. Either way, the only thing on any pilot’s mind is get it on the ground…preferably where there are emergency services to tend to injured passengers and possibly keep the fire under control while they egress. Some divert fields do not have these services, which may explain the left turn to head back to Kuala Lumpur. Fire also explains the rapid climb since the pilots may have dumped the cabin pressure and rapidly ascended to try to starve the fire of oxygen and then dove back down before those same conditions affected the passengers (who were no doubt on the emergency oxygen supply at this point).


2. Rapid/Explosive Decompression: If cabin pressure is suddenly lost, a rapid descent is critical to get to an altitude where people can breathe. Time of useful consciousness above 25,000 feet is very limited. It does not explain the rapid climb but does cover the low altitude flight and left turn factors. Even if the aircraft could fly for many more hours at reduced speed and low altitude, no pilots would subject their passengers to an unpressurized flight any longer than absolutely necessary.

Allow us to use logic in this, not emotion or sensationalism. Whichever scenario you look at, they all entail a crew reversing course, possibly with a stricken craft. Regardless of the cause of the problem or if it was a combination of factors, the logical next step is to assume they were looking for Kuala Lumpur. If there was degradation of the inertial navigation system, if there had been multiple electrical failures, then it stands to reason that old school navigation with the whiskey compass had to be used. Add in a reduced altitude and their visibility over the horizon would suffer. The pilots would know how long they had been in flight since departure and how long it was until the unfortunate event and thus calculate how long it would take to return at an undoubtedly slower airspeed. Perhaps this time came and went, prompting them to assume they missed their target. Would it make any sense for them to continue in a straight line?

At the risk of sounding like a media know-it-all, the flight will probably be found within an hour’s worth (or less) of engine-out cruise speed of Kuala Lumpur. Like a car in an unlit neighborhood at night, they knew they had passed it and another course reversal was required, but how much? How much of their navigational gear working? Could they see stars and take a guess at which way was which? Was smoke in the cockpit, obscuring their vision? Given that the communications stopped and did not resume, at least some of the avionics were adversely affected. How close did they get to the airport but simply not see it because of altitude or other factors?

I refuse to speculate on the cause of the events that led them to rapidly climb and then dive down to what amounts to a lost-pressurization altitude (even engine-out ceilings are higher than 12,000 feet). If it was a battery with thermal runaway, a mislabeled hazardous cargo, or even an intentional detonation device, it is immaterial. The end result is the same and we still cannot locate the wreckage. Let us cease grabbing at straws and start grabbing at facts and probabilities. That is all we have to work with. Unfortunately, it seems that the crew and passengers of Flight 370 weren’t even given that on the night of March 8th, 2014.


With deepest condolences to the families of the passengers and crew.

Know It All…Or Not

If I have to repair this in flight, something is beyond horribly wrong.

If I have to repair this in flight, something is beyond horribly wrong.

I punched a fist of joy into the air upon reading Bruce Landsberg’s recent editorial in the February 2014 AOPA Pilot magazine. He addressed the topic of useless knowledge being taught rather than critical overall concepts. I’ve been saying this very same thing for years, but since I don’t have a type rating in the Saturn V, I’m viewed as a dangerous menace to the national airspace system. Thankfully, his article lends credence to my stance that we often focus on useless data in aviation that is of little practical or emergency use. We should be looking at the big picture items with a lot more interest rather than the little details that only impress other pilots or examiners.

While I’d love to claim credit for being a maverick as it relates to the idea of not needing to know everything there is to know about an aircraft, NATOPS was leading the way with this mindset years ago. Anyone who has flown in the US Navy knows that the manuals for aircraft are purposely designed to exclude excess systems information. The only things that are included are things that the pilot either has control over, or any system that can cause a hazard to continued flight (and how that hazard will manifest). The reason is simple: mechanics fix airplanes and pilots fly them. This division of labor is present even in civilian aviation where the FAA makes it a point to tell pilots that save for a few preventative measures; they are not allowed to be a mechanic on their airplane.

I believe this focus on knowing every system in detail is a holdover from the good ole days of aviation (which we simply cannot move on from it seems). Systems were very complex and highly mechanical in nature. All of them were controlled by human beings, hence the plethora of people in the cockpit of vintage airliners. The flight engineer literally made sure all the systems operated the way they were supposed to. The pilots flew and if present, the navigator made sure they didn’t get lost. The crew had to understand their piece of the equation and at least a little bit of the other guy’s in order to pull off the flight.

Fast forward to today where the airplane’s flight engineer is the ECAM that collects and displays information about the status of every system several times per second. You literally don’t need to know much more from an operational standpoint for many systems other than “Is it on?”, “Is it off?”, and “Should it be in that state?” A friend of mine flies a Brazilian-built regional jet and has to memorize the starting and operating temps, abnormal shutdown criteria, and various RPM ranges…for the APU. Meanwhile, the only direct control over this device the pilots have is an Off-On-Start switch, a Stop switch and an emergency fuel shut-off switch (in the event of a fire, overspeed or overtemp, the APU FADEC will automatically command a shutdown). Does it make sense that three switches with a total of five possible selections warrants memorizing the type of compressor, every temperature limit, every RPM limit, and the type of cooling used by the APU?

While it may be interesting information to know, the role of a modern airline pilot is not to play mechanic. It is to fly the aircraft from Point A to Point B. If there is a problem with the aircraft, they write up what isn’t working and if it isn’t on the MEL, continue flying until it can get fixed by the maintenance guys. It’s not about being cavalier, it’s about being efficient with specialized skills. Ask yourself if there is any way for a motivated captain to crawl back to the tailcone in flight (there isn’t since the APU is surrounded by a firewall). Even if they could get back there, what could they do to fix a problem? Last time I checked, airlines don’t hand pilots toolkits with their Jepp revisions. What if more time in review and sim sessions was spent talking about things that are more likely to be encountered in day-to-day operations, rather than the specifics of a component that the pilot will most likely never even see and has limited control over?

Air France 447 is a perfect example of why broad scale knowledge is critical. An aircrew faced with a rare and confusing situation may be spring-loaded to go to a rather complex solution due to the way we train them. Ignoring the control input issues, had the crew been taught to look at the big picture of where is the information coming from, they might have considered the fact that the FMGS was likely showing correct groundspeed based off the GPS signals it automatically updates with. Additionally, the combination of pitch and power for a given flight condition would have led to suspicion that the EFIS PFD was at least partially lying (and thus to look for independent data, such as the FGMS). This is not an indictment of the crew, but a look at how a few seconds to consider the big picture before zeroing in on a smaller picture solution may prevent accidents like this from happening again.

The Air France accident was not the first time a high performance jet was lost at night in the vicinity of thunderstorms due to faulty instruments. A nearly identical situation occurred in a B-58 on February 14th, 1963 when the pitot tube iced up and the pilot began unknowingly following erroneous airspeed data. When the controls felt sloppy and he suspected something was wrong, the pilot cross-referenced with the Machmeter, but this was also giving an incorrect reading. It wasn’t until the pilot asked the navigator (who had an independent pitot system) what the airspeed was that he realized the delta-winged bomber was about to drop out of the sky. The aircraft ended up departing controlled flight and the crew members were forced to eject (see the article “B-58 Hustler” by Jan Tegler in the December 1999 issue of Flight Journal for the entire story). Hopefully with changes in training and multiple-source independent airdata, there won’t be any more accidents like these.

Aerodynamics is another place where we overthink things to the point that it might be causing poor decisions in some situations. My favorite horse to flog is the recent bank angle conservatism being taught in the United States. There is no magic law of aerodynamics that says if you bank 31 degrees at 999 feet AGL, your airplane will autorotate into a flat spin. Although the intentions are good, the source of this fear stems from the g-load charts that we all looked at as student pilots. In a 60 degree bank, load factor is doubled and stall speed increases substantially. The only problem is that this is only true if you attempt to maintain altitude. It is not even close to accurate in a descending turn. Nor is it accurate if one is flying an airplane with a lot of excess power/thrust. We have become so obsessed with the book numbers that the bigger picture of how aircraft actually fly in three dimensions is being lost.

Don't freak out if you hit 60 degrees of bank while descending.

Don’t freak out if you hit 60 degrees of bank while descending.

There are student pilots (and an increasing number of certified pilots) who will either fly C-5A sized patterns, or make skidding turns in order to keep the bank angle low. The former negates the engine-out glide advantage of a close pattern while the latter actually is a perfect setup for a spin. To be honest, a bank beyond roughly 30 degrees is not really necessary at speeds under 80 knots if the proper lateral spacing is used. The trap is when the pilot comes in a lot faster or much closer due to ATC request or their own misjudgment. All of a sudden as they notice they’re going wide, the rudder gets kicked in and opposite aileron starts to hold the bank angle constant. The saving grace is that usually this situation is created by having a surplus of airspeed so a spin isn’t likely provided they return to coordinated flight fairly quickly. Rather than worrying about a chart that isn’t applicable to their conditions, they should be taught the confidence to put the airplane where it needs to be to get where they want to go.

Again, before people get riled up, there is a time and a place for sticking to book numbers. Early 727 pilots who tried to eyeball the landings as if it was a DC-3 with jet engines learned about the importance of sticking to the book. But the book isn’t magic. The numbers it contains are the sum of the properties of the atmosphere plus the aircraft’s design plus the systems installed. If it takes the engines 9 seconds to spool from flight idle to “Oh crap” thrust, the obvious solution is to not be low and slow while at idle. You don’t need to know how many stages are in the low pressure compressor (six total, two fan and four compressor) to get the big picture of why you keep the power up on final. Knowing the big picture of how heavily loaded swept wings behave at high angles of attack will also give you a better understanding of why simply lowering the nose won’t immediately get you out of trouble (plus the delay in thrust buildup to further compound your woes). It is true that sticking to the book will ensure that you arrive safely, but it is better to understand both the concept and the details.

Pilots cannot and should not know it all. The FAA regulation to “Familiarize yourself with all available information concerning that flight” is a rule designed so that if a pilot makes any error that “reckless and careless” doesn’t cover, the book can still be thrown at them. Rest assured that if you put one into the ground a half-mile short, you’re getting blamed for not getting a weather briefing despite it being CAVU with calm winds, flying an aircraft with an inoperative ADF and for not knowing the airport manager’s office phone number . This is a poor way to ensure safety but a great way to have instant blame in the event of an incident. Instead of scaring pilots into trying to read everything to fit some liability model, we should be encouraging them to select the appropriate data for what they want to do.

We collectively have to accept that despite what we would like to have everyone believe, 99.2% of pilots will never know every single little detail about their airplane. This should be instilled in student pilots via the way they are taught. Start with the basics and allow them to get used to the 3rd dimension. Instead of filling their heads with regulations from day one, ease off and let them enjoy flying. Let them have a few hours of wrapping their heads around controlling the airplane before revealing that they’re going to have to become a lawyer as well to understand all the regulations. Instructors can easily move from the big picture of “Let’s do our maneuvers up high so if you make a mistake we have plenty of room.” to the verbatim description of FAR 91.303 over the course of their training. The rules will make more sense anyway if a little bit of experience and common sense are applied rather than “you need to know this for the test”.

As usual, I’m sure not many people will read this (especially this far down) and those that do think I’m either full of myself, dangerous, a crusader or a combination of the three. The truth is I love aviation but I’m also willing to point to where we can do a better job making it less daunting for newcomers to get involved, safer for those already flying and more enjoyable for everyone. If we are honest, it’s time to admit that the act of flying is not very difficult in execution. Judgment on the other hand is what kills people. Being able to recite regulations does not stop people from flying into IMC or descending below minimums. Only the proper attitude and respect for the fact that you’re suspended in the air by the laws of physics and aerodynamics will make a person accept their own limits and those of their aircraft. This must be stressed more than any chart, schematic or diagram.

BMI Tests For Pilots: Avoiding The Issue

(This article was originally published on my fitness site but due to its inherent focus on aviation, I’ve posted it here as well)


The proposed addition of neck circumference and BMI testing to the airman’s medical exam is inaccurate, misguided and of limited usefulness. The impetus behind this screening is the recent spate of tired pilots making mistakes and even falling asleep while on duty. In one such incident it was later revealed that the captain had sleep apnea which was viewed as a probable cause for his falling asleep enroute (since sleep apnea is not contagious, the reason for the first officer also falling asleep at the same time was chalked up to fatigue). While this change to the medical exam affects all pilots, including those who fly privately, this piece will focus on air carrier pilots.

Aviation is under a constant media microscope and these incidents while statistically miniscule, nevertheless raise the suspicion of the public. Falling asleep at a job as hazardous as those that exist in aviation should not be tolerated, but using a questionable screening process should not be accepted in an attempt to create a solution to a condition that may or may not exist and most likely is not the primary cause of exhausted pilots. For the record, each year there are over 100,000 motor vehicle accidents that are attributed to drowsy driving. Despite the loss of 1,500 lives, so far no public safety department has mandated obesity or sleep apnea tests for motor vehicle drivers, even commercial operators.

Body Mass Index Accuracy

It has been proven that people with extremely high body fat percentages are susceptible to obstructive sleep apnea. It has also been proven that sleep apnea causes both hypersomnia and insomnia, impairs cognitive function and can lead to cardiac arrest in extreme cases. These facts are also not in question. What is troubling is the method being used to determine this risk factor in pilots, namely, the BMI rating.

BMI, or body mass index is a handy method for calculating a person’s mass to height ratio. As such, it is useful as a quick evaluation concerning obesity. The problem with BMI is that it is a very “dumb” equation; it does not know what it is measuring. A “smart” doctor, trainer, or clinician has to interpret the number and take into account other physiological factors (even the CDC states that BMI is not a diagnostic tool). Unfortunately, because BMI requires no specialized equipment or tactile measurements on the patient, it is widely used by people who have limited knowledge about the human body, obesity, bone density or muscle mass. This results in gross misinterpretations and misdiagnosis for people of various body types.

Another problem with BMI is that it leaves out critical factors such as age, gender, and body fat percentage. As people age, they naturally lose muscle mass unless steps are taken to preserve it (such as lifting weights). The loss of muscle mass, while detrimental, will show up as a reduction in BMI, leading the patient to think that they are getting healthier. Women on average have less muscle mass than men, resulting in more women being classified as healthy and more men as obese, even if the opposite is true. And most tellingly, if a person is 5’8” and 190lbs with 8% body fat, they will score the same BMI as someone who is 5’8”, 190lbs and 30% body fat (it is the same logic as saying that a Ford F-150 and a Ford Mustang will perform exactly the same since they have the same horsepower). One would think that scenarios such as these would be easily noticed and accounted for, however that does not appear to be the case in several well publicized instances.

In recent months, stories have come out where middle schools with good intentions unwittingly labeled some student athletes as “at risk” or obese based on a BMI calculation. The fact that nobody in charge of the program even understood how to deal with off-scale errors caused by a student having more muscle mass than their peers is distressing. Part of this rampant misinterpretation stems from our nation’s obsession with weight as the be-all-end-all indicator of a person’s health. Weight alone is a useless metric. It merely tells us how much of an effect gravity has on a given person. It does not tell us the distribution of body fat or muscle mass, which are the critical values that directly affect a person’s well-being. And as previously mentioned, simply possessing the stats of being 5’8” and 190 lbs only means that you are 5’8” tall and 190 lbs. Any other inferences must be determined by checking body composition.

As angry as the students and parents were at this mislabeling, imagine if your job relied on BMI numbers that may not have any basis in reality. It has been shown that it is very easy to make sweeping generalizations based on spurious data and then pass off any errors as anomalies. Will an airline ignore high BMI numbers in a visibly fit pilot, or will they tell them to atrophy away some muscle mass in order to lose weight? Alarms should be going off in the head of every pilot in America. If it can happen to children in school, it can and is about to happen to them as well.

Flight Fatigue

The cockpit of a modern jetliner can be a very sleepy place physiologically speaking. Noise fatigue from the slipstream roaring past the windows (a very effective white noise generator), reduced oxygen levels even with a pressurized cabin, and the inability to simply stand up and walk around are just some of the fatigue inducing factors present. Any one of these factors by themselves are hazardous enough to have volumes written about their attendant risks. Somehow, they are not even mentioned as a possible factor in pilot fatigue in this new screening process.

In fact it is entirely possible that it is an attempt to divert attention away from the fact that the new rest rules enacted by the Federal Aviation Administration have not fully accomplished their goal of eliminating pilot fatigue. This is only because airlines are not required to fully implement these rules until the end of 2013. Federal regulations now allow air carrier pilots a maximum of 9 hours of flight time and at least 10 hours of rest per each 24 hour period. To those who don’t fly for a living, a 9 hour workday does not sound that difficult and 10 hours of rest seems like it should be adequate. In reality flight time only accounts for loggable time in the aircraft (in airliners, the parking brake serves as the aviation equivalent of a time clock).

The new rules do a much better job of eliminating fatigue due to deadhead commuting and excessive duty times. Preflighting, checking weather, waiting for ground stops to expire, briefing, and all other tasks directly associated with preparing to fly an aircraft are limited to no more than 14 hours per day. Unfortunately, traveling to the airport, leaving the airport and checking into hotels all accounts for time that is not yet definable by the FAA.

Confusion abounds in the general public as to how a pilot halfway through a 3 hour flight can fall asleep. While that one flight is only three hours, it may be the second flight that day on the third day of a four day trip away from home. Anyone who works 9 to 14 hours is going to be tired. Anyone who works 9 to 14 hours going back and forth between time zones, sleeping in unfamiliar beds, unable to establish a consistent exercise regimen and not having access to healthy, agreeable foods is going to be even more tired. Now ask that person to stay alert in an environment that is almost custom built to induce sleep for four days in a row. This is the real reason why pilots are tired, make mistakes and fall asleep. When two pilots fall asleep and overfly their destination, or when critical mistakes are made due to fatigue induced cognitive impairment, the last thing that should be looked at is sleep apnea. Is sleep apnea a risk? Absolutely, but in the long list of causal factors it is not anywhere near the top.

The combination of desire to generate profit, maintain public confidence in aviation and ensure pilots are not forced into unhealthy patterns is a difficult river to navigate. The FAA has tried to close a massive loophole in their prior regulations via their current definition of Flight Duty Period. Airlines have historically exploited this oversight and were against changes to the Flight Duty Period limits (see page 112). Currently the issue is that duty time ends once the aircraft is parked, not when the pilot arrives at the hotel (we are assuming the pilot is in the middle of a multiple-day trip and cannot simply go home). It can easily take an hour to go from the cockpit to a hotel room, sometimes more. Assuming the pilot eats immediately, that leaves roughly 30 minutes before they are supposed to be sound asleep in order to take advantage of the “8 hour uninterrupted sleep opportunity”. In the morning, the reverse is in effect as it takes a similar amount of time to get to the airport and check in at the crew room. It is easy to see how the 8 hours of sleep can quickly erode to 6 or less. As a good friend who flies for a major air carrier said, “The new rest rules need to address the fact that we can’t go to sleep while making the first turnoff, nor can we wake up at V1.”

Instead of neck circumference and BMI tests,  there should be demands for better scheduling practices for all air carriers. Require that pilots get up and walk around the cabin for a couple minutes every hour (security rules be damned). Mandate that pilots take a few breaths from their O2 masks whenever they feel tired. Implore the FAA to close the final loophole in the definition of Flight Duty Period. Consolidate preflight tasks or delegate them to a dedicated ground crew much like military does with its crew chiefs. Install better soundproofing insulation in cockpits to reduce noise fatigue and hearing loss. Encourage airlines to create dedicated “pilot apartments” at their bases to eliminate travel time for the crews. Any one of these potential solutions solves multiple major issues facing pilot workplace health, which is the most effective way of mitigating the fatigue issue.


Should obesity screening be conducted? Considering that airline pilots must possess a 1st class medical certificate which can only be obtained after a battery of tests including an EKG, it seems odd that severely obese pilots are just walking around by the thousands. Many aircraft are tough to fit into even for an average sized person, so there’s yet another barrier to the truly obese sitting in the cockpit. But for the sake of argument, let’s say that there is a sizable population of obese pilots. There are far more accurate methods of determining levels of adipose tissue distribution than a distorted height to weight ratio. Aerospace Medical Examiners are certainly intelligent enough to use methods such as caliper skinfold or bioelectric impedance to make the necessary measurements. Then that physician can make recommendations on what the pilot can do to reduce their body fat percentage. Focusing on body fat, not weight, will have a far more effective result on the pilot’s overall health than zeroing in on one potential condition.

Flying aircraft is mentally and physically taxing. Pilots are still just mere mortals who have the same body the rest of us have. It requires food, exercise and sleep or it will not function optimally. To expect them to operate like machines is not realistic. Airlines need to accept this, the FAA has to continue to support this and pilots themselves have to live with this. Until it is determined that fixing the underlying causes is worth the cost, we will continue to see more pilots making fatigue induced errors and overflying destinations while fast asleep.

Suggested Further Reading

Center For Disease Control: “About BMI For Adults
Sept 13, 2011
FAA: “New Obstructive Sleep Apnea Policy” ; Fred Tilton MD
November, 2013
Mayo Clinic: “Sleep Apnea
July 24, 2011
FAA: “Fact Sheet – Pilot Flight Time, Rest and Fatigue
January 27, 2010
FAA: “Flightcrew Member Duty and Rest Requirements
December 21, 2011
The Sleep Foundation: “Sleep Studies
National Institutes Of Health: “Neck Circumference And Other Clinical Features In The Diagnosis Of Obstructive Sleep Apnea Syndrome” ; Robert J.O. Davies, Nabeel J. Ali and John R. Stradling
October 24, 1991
NHTSA: “Drowsy Driving And Automobile Crashes” ; Kingman P. Strohl MD, et al
International Journal Of Obesity: “Accuracy Of Body Mass Index In Diagnosing Obesity In The Adult General Population”; A. Romero-Corral, et al
February 19, 2008 “Summary Of Pilot Medical Standards
February 26, 2007

Six Degrees For Separation: One Way To Solve The DFW Airspace Issue

The airspace over Addison (KADS) is slated to be changed soon if the FAA proceeds with its plan to reduce congestion into Dallas Love (KDAL) and Dallas/Fort Worth (KDFW). The airspace change includes a lowering of the Class D over Addison from 3000 MSL to 2500MSL. While that may not seem like much, it is in an area where operations are already in a very tight fit with DFW traffic to the west, DAL traffic inbound from the east-northeast and large amounts of corporate, fractional, cargo and training traffic underneath at ADS. In fact, the final approach fix (JERIT) for ADS rwy 15 is at 2000 MSL, which would leave only 500 feet separation between IFR arrivals into ADS and DAL traffic at 2500 if this airspace change goes through. As it stands, ADS is already the busiest GA airport in Texas and in the top 5 in the United States.

The area of concern: The 3000 MSL roof of Addison's class D is slated to be lowered to 2500 MSL, leaving very little space for aircraft as big as MD-80s and 737s to maneuver. The proximity to DFW and DAL is noteworthy.

The area of concern: The 3000 MSL roof of Addison’s already highly modified class D is slated to be lowered to 2500 MSL, leaving very little space for aircraft as big as MD-80s and 737s to operate. The proximity to DFW and DAL is noteworthy.

There are numerous ways to avoid having to redesign the existing airspace. Although I’m sure some will suggest vectoring airliners further to the north and west before their southbound turn towards DAL, this is not efficient with respect to the jets. Anything that increases fuel consumption for the airlines is not only irresponsible environmentally, but financially. Likewise, the hundreds of businesses that rely on ADS should not be marginalized in the effort to reduce the impact to airliners. I am not writing this from the standpoint of “big airliners are against little piston planes”. Instead, I am writing this as the result of several years of observing, studying and testing new methods of utilizing existing airspace. After reading the NPRM on the changes to DFW’s airspace, I came to the conclusion that people may not be fully grasping the true capabilities of modern jet airliners.

The upside-down wedding cake design of Class B airspace is optimized for steep climbs and descents. Standard Class B has a floor gradient of 300 ft/nm out to the 10nm ring. This equates to only 1000fpm at 200ktas or 1250fpm at 250ktas. But again, this is for the floor and operations in excess of these values would be well contained within the airspace. With the advent of RNAV STARs and GPS approaches, creating 3D highways in the sky is no longer a fantasy but an easily employable system that works in VFR or IFR conditions. The only way to fit more aircraft into the volume of airspace already set aside is to increase the angle of descent at critical segments inside the Class B.

For separation and flow purposes, many congested terminal areas drop arrivals down 30 or 40nm out so that departures can climb unobstructed above them. This is because in areas like the DFW Class B, the proximity of DFW, DAL, ADS, AFW, NFW, FTW, GKY, GPM and RBD makes it very hard to get everyone where they need to be at the same time. When most of the non-RNAV STARs were designed, it was hard to conceptualize how to position aircraft three-dimensionally. Now that airliners and many corporate aircraft feature VNAV, FPA symbology and the ability to climb or descend in excess of 2000fpm, being able to follow a constant descent path is much easier to plan and execute.

As mentioned before, the standard floor gradient for Class B is 300ft/nm. Modern jet aircraft can climb at more than twice this rate under most conditions. Descending is actually more difficult to manage in some cases as an angle which is too steep will preclude deceleration to flap and gear speeds. Testing this theory in various sims, talking to pilots of different aircraft and flying the procedure in real aircraft has shown that an average glide angle of 6 degrees results in a power-off approach with no increase in airspeed (in reality the range was roughly 4.5 to 7.0). Depending on configuration, very low levels of power may be required to maintain airspeed. This power setting will invariably be less than that used during the current step-down method of approaching. This has tremendous advantages for noise abatement, fuel conservation, airspace utilization and wake turbulence avoidance.

Jets are not as responsive as light GA airplanes in the approach phase which is why a 6 degree glide path converts to a standard 3 degree glide path at some pre-dplanned distance from the runway, most likely 1500 to 1000 AGL (depending on the aircraft type and wind conditions). Further out in the Class B airspace, descent angles can be more conventional if satellite airport conflicts are not present, allowing jets to “pre-configure”; going to a minimal flap setting that would produce enough drag to keep speed from increasing in the descent. Some aircraft that are extremely clean with high inertia such as the A330 and B777 may require shallower angles or the use of speedbrakes.

Using this type of approach in the northeast sector of the DFW Class B would bring Love arrivals over Addison between 3000 and 4500 MSL (depending on where they are vectored from). This is a substantial safety margin for both Addison and Love arrivals. An additional benefit is that Love’s lateral spacing would not have to be modified from what exists today, reducing the potential for conflict with Dallas/Fort Worth traffic on the Cedar Creek Six arrival when a south flow is in use. Around the DFW Class B, departures leave the terminal area on north, east, south and west headings, while arrivals enter on northeast, southeast, southwest and northwest headings. This existing deconfliction works well with 6 degree descent angle as departures would not risk losing separation with arrivals.

The whole idea behind the 6 degree approach is to use what we already have without making any particular group of operators have to suffer. If the procedure works well in our airspace, it can easily be implemented nationwide for reasons as varied as traffic management, noise abatement and reduced emissions. Please try this procedure in whatever simulators you have access to. An example to test out is DAL runway 13L, crossing WADES at 7500 MSL, NITER at 1900MSL and conducting a normal visual or ILS once crossing the FAF. Since this is an angle-based and not a rate-based procedure, your VS will change as you descend and or change airspeed.

KDAL ILS 13L 6 Degrees

Runway 13L Dallas Love. Note the modified IF crossing altitude to produce a 6 degree glideslope to the FAF.

If you want to convert any IAP to a 6 degree variant, simply decide what your conversion altitude or intersection is (when or where you go from 6 to 3 degrees) and how far back from that point you want to commence the approach. Applying basic trig will net you the IF crossing altitude. For example using DFW’s runway ILS 17L:


IF = RIVET, Unknown MSL, 12.6nm from FAF

sin descent angle x distance to FAF x nautical mile in feet + FAF altitude

((sin6 x 12.6) x 6076)) + 2300 = 10302 MSL at RIVET

KDFW ILS 17L 6 degrees

Runway 17L Dallas/Fort Worth Intl. Notice the modified crossing altitude at the IF.

In the meantime, please send the FAA your comments and suggestions on the proposed airspace change. My solution is not the only one and the more minds that work on this issue, the better.!docketBrowser;rpp=25;po=0;dct=PS;D=FAA-2012-1168



Aerobatics Undefined

At the airport the other day, we got into a discussion of FAR 91.307, lovingly known as the “parachute” or “aerobatics” reg depending on who you talk to. The point of confusion was that an instructor had been told by another pilot a while back that doing spins was illegal since they weren’t wearing parachutes. The concerned pilot had seen 91.307 (c) and assumed that since spins exceed 30 degrees of pitch in most cases, that the reg had been busted. However, reading further to 91.307 (d) (2) it clearly states that spins and other checkride-required maneuvers are legal to fly without a parachute. In fact, there is no restriction on attitudes whatsoever provided everyone in the aircraft is a crew member. Actually, 91.307 (c) gives us a lot more latitude than we think. It states the following:

(C) Unless each occupant of the aircraft is wearing an approved parachute, no pilot of a civil aircraft carrying any person (other than a crewmember) may execute any intentional maneuver that exceeds–
(1) A bank of 60 degrees relative to the horizon; or
(2) A nose-up or nose-down attitude of 30 degrees relative to the horizon

If you and a fellow pilot go up and do a 90 degree bank wingover, you do not need parachutes. If you go up solo and pitch up to 50 degrees and do a reduced-G float over the top, that’s legal without a chute as well. If you take your non-rated friend up, you either have to provide parachutes for the both of you, or keep the angles to the 30/60 limit. Also, if you and 3 other pilots go up, the 2 pilots in the back seats do not count as crewmembers so the 30/60 limitation will also apply. Note, that 30/60 is not the boundary of aerobatic flight. The litmus test for what defines aerobatics for your aircraft is in the operating manual. If your manual states that aerobatics are not approved except spins, Chandelles, accelerated stalls and Lazy-8s, then you know that rolls are out of the question. But nowhere in the FARs does it describe aerobatic as being flight in excess of 30/60 degrees. FAR 91.305 defines aerobatic flight as:

For the purposes of this section, aerobatic flight means an intentional maneuver involving an abrupt change in an aircraft’s attitude, an abnormal attitude, or abnormal acceleration, not necessary for normal flight.

That’s pretty vague, probably one of the most open ended regs next to 91.119. What defines abnormal? What is abrupt? And what is normal flight? I get the feeling when this was written, it was with point to point transportation in mind. As such, the regulation is conspicuously open-ended to allow for other types of operations that involve more aggressive maneuvering. The catch is that the FAA can also randomly define what “normal” and “necessary” is in response to a complaint or to issue a violation. But there is still another catch. “Aerobatic” also counts as a category of aircraft.

Say that I’m out over farm fields at 3,000 feet AGL in a utility category airplane doing wingovers. My airspeed never even gets into the yellow arc and my G-load never goes over 2.0. An overeager observer down below assumed that I was “hot-dogging” and “barnstorming” and called the FAA to say that I was doing “flips and tailspins in a Piper Cub” (it’s always a Piper Cub to non pilots). Short of having a data recorder onboard, its my word against theirs. Lacking this hard data, its very hard to validate what you did or did not do. And knowing what maneuvers were flown is critical in order to defend yourself. After all, it is entirely possible to do “aerobatics” in normal category airplanes without imposing more than 2Gs on the airframe. Before you get angry and call me dangerous, I’ll explain.

While it would be tempting fate to do a snap roll in a normal category aircraft, you can freely apply full control deflections (well below Va and in one direction only), pitch, roll or yaw to whatever attitude you like. The danger is in building up too much speed in an extreme nose low attitude and needing to pull more G than the airframe is rated to (that’s when you hear the loud POP and then enjoy the rush of the wind as your wingless, tailless airframe plummets to earth). However, an abrupt change in attitude does not always imply a high load factor. Imagine using full aileron in a Piper Saratoga to roll into a steep turn (50 degrees) quickly. Was the maneuver abrupt? Compared to “normal flight” in the same type airplane, yes. Is the attitude abnormal? Not really? Was the acceleration abnormal? Not even close. So was it aerobatic? Ask your FSDO…seriously, find out how they define it.

The more knowledge you have about what you’re doing, the better. An untrained observer may say that they saw an airplane doing “acrobatics” and “stunts” when really you were doing Chandelles. If you can confidently state what maneuvers were performed along with some rudimentary info on entry altitudes and speeds, it may convince whoever is inquiring that you aren’t just throwing the stick around to see what happens. Unfortunately, society loves to point out when they think someone else is doing something wrong or unsafe without actually knowing what was going on in the first place. If you take the chance of actually having fun in other than straight and level flight, there’s the risk that someone with an iPhone is going post video of everything you did while commenting on how “unprofessional” and “dangerous” the pilot of that little airplane was.

Quite frankly, every time you fly, you are at the mercy of someone’s self-narrated cellphone video (even an airplane well above 1,500 feet AGL will show up on a phone camera). The only way to protect yourself legally is to make sure you understand the regulations fully. However, the only way to keep yourself alive is to make sure understand the aerodynamics fully. Use 91.307 to your advantage. Go up with an instructor and practice really unusual attitudes. Take some aerobatic lessons. Get used to the fact that airplanes operate in a three dimensional ocean of air. If your comfort zone ends at 30 degrees of bank, work your way up to 45 and 60 degrees (maybe even a little beyond). Once you experience that an airplane will not just drop out of the sky because the bank angle increased beyond 45 degrees, you will have a lot more confidence in handling it in all phases of flight.