Obesity and Fat Aircraft – a Weighty Subject for General Aviation

by HPA · January 31, 2016

Heavy-Scale-CroppedObesity and Fat Aircraft

A Weighty Subject for General Aviation

Douglas Boyd Ph.D.

As any pilot knows from primary training, safe flight operations require that the airplane be loaded within the maximum certified weight and center of gravity (CG) limits. Increased aircraft weight, be it due to occupants, cargo or both, adversely affects aircraft performance in a variety of ways. For example, longer takeoff and landing distances are required for a heavier aircraft and climb gradients are more shallow. Ignore such limitations and one runs the risk of a runway over-run (of particular concern when the runway is followed by descending terrain or water), the inability to clear rising terrain in the flight path, airframe failure under turbulent flight conditions or loss of control. Keep in mind too that weight-dependent performance degradation is further exacerbated with an aging aircraft. The average age of the general aviation, single engine aircraft is more than thirty years. Performance of aging aircraft typically diminishes from that stated in the pilot operating handbook/flight manual for a plethora of reasons e.g. airframe deterioration (causing parasitic drag), weight gain (e.g. addition of after-market products, residual wires in avionics replacement, moisture absorption into cabin insulation) and reduced engine performance.

Airframe deterioration Image_1

Fatality of Accidents for which Weight/CG Limits Exceedance was Causal or a Factor

What is the accident and fatality rates for these types of accidents in general aviation? Well, there’s good news and bad news. Starting off with the good news, a search of the NTSB database for general aviation accidents related to operating the aircraft outside of it weight/CG limits shows a modest, static rate (about 2 per million flight hours) over the past 25 years. The bad news however, is that the majority (57%) of these types of accidents are fatal. That’s substantially higher than the 21% for accidents unrelated to operating a single piston-engine aircraft outside of its weight/CG envelope. Digging a bit deeper and one finds that for weight/CG-related accidents the overwhelming majority (77%) are due to an overloaded aircraft operating WITHIN its CG while only 5% of accidents are due to a CG located forward or aft of the designated limits. Exceeding both the maximum weight and CG limits accounts for the remaining 18% of the accidents.

Is it Safe to fly an Aircraft just over its Maximum Certified Weight?

Let’s focus on the types of accidents where the aircraft weight is over that for which it is certified but nevertheless the airplane is within its CG limits. Anecdotally, some general aviation pilots consider operating such an aircraft to be safe.

Not so. In fact, for this subset of accidents, just over 50% are fatal.

Furthermore, the NTSB database shows us that the proportion of fatal accidents for aircraft modestly over the maximum certified weight (1-122 lbs. in excess) is actually higher than those for which the aircraft was substantially (123 lbs. and more) in excess.

Why do Weight/CG Exceedance-Related Accidents Carry a High Fatality Rate?

Of course this begs the question as to the reason(s) for the dis-proportionate number of fatal accidents related to operating the aircraft outside of its weight/CG envelope. There could be a plethora of possibilities. For example, remember that increased aircraft weight requires increased lift and, as a corollary, a higher landing speed. Since the impact force exerted on the occupants is a square of the velocity, crash forces exerted on occupants of an aircraft loaded beyond its maximum certified weight is increased. Another possibility relates to a degraded climb gradient yielding controlled flight into terrain. Third, a stall with an aircraft loaded aft of its CG limit is difficult to recover from. Lastly, airframe failure may occur under turbulent flight conditions where the aircraft is loaded beyond its maximum certified weight.

Other “Weighty” Stuff

Pilots should be cautious in taking self-reported occupant weights “as gospel” for weight/balance determinations. As humans we tend to be vain (irrespective of gender!) so often these numbers are under-estimated. Consider keeping a scale in the back of the plane for your “human manifest.” Also, be careful about using non-FAA approved software applications for aircraft weight-CG determinations. While these allow for a quick, easy determination of aircraft weight and CG location, keep in mind that these applications utilize a generic aircraft. For example, throw in an after-market air-conditioner for your plane and usable loads/CG limits can be reduced dramatically as evident for this twin-engine Beech Baron (image 2).

Wt and Bal Image2

Summing Up

The notion held by some that flights with an overloaded aircraft within its CG limits are “safe” is flat wrong. Operate an aircraft outside of its weight/CG limits and you become a test pilot. Unless you want to become included in the annals of the NTSB avoid the temptation! Second, be wary of using self-reported passenger weights. To quote a prior President, trust but verify. Finally, when using online apps for weight/CG determinations confirm that the basic empty weight of your aircraft is in agreement with that stated in the application.

Douglas Boyd Ph.D.Douglas Boyd Ph.D. Commercial/IFR SMEL (Citation 500 type rated) researches the causes and trends in general aviation accidents publishing his work in peer reviewed scientific journals including Accidents Analysis and Prevention. Douglas is a member of the Aerospace Medical Association safety committee and the FAA Safety Team (FAAST).




How it Started

One of my best friends in high school, (Doug Gray) was a private pilot. He offered to take me up for a flight in a 1967 Cessna 150, N6228S. We took off from Calhoun, Georgia, and he took me on a scenic tour of the area, I was hooked. I later found out that my English teacher, (Jan Haluska) was also a flight instructor and the school was offering a ground school course the next year, which he taught, along with flight training with the goal of becoming a private pilot. I managed to talk my dad into funding the training, at the time the total cost was right around $500. Cessna 150 rental rates where $12 an hour, and the 172 we used for cross country was $15 an hour including fuel.

Training Begins

It started August of 1977. The fall semester rolls around, and I am enrolled in ground school, and if memory serves me, we met twice a week. First came the paperwork for my student pilot certificate, which at the time was included with the 3rd class medical. I loved ground school, especially learning navigation, plotting courses on the sectional, again this was before iPads and GPS, so we did a lot of dead reckoning and VOR navigation for cross countries. At the end of the course, I made an 83% on the Private Pilot written exam, remember this was before we had the question-and-answer books that on future test I would consume before taking a written.

2022.06.09 11.19 Flyhpa 62a27fea7716a


The fun really began on August 22, 1977, it was my first flight. To my surprise we used the same Cessna 150, N6228S that my friend Doug Gray had taken me for a ride in. The Cessna 150 had a standard VFR instrument panel, with one NAV/COM, and one VOR CDI. No intercom, so no headset, at the time I didn’t know what I was missing. I didn’t get my first headset until I started my instrument training in 2003. I was a big guy, I was 6’ 4” and weighed 245 lbs. but I do not remember being uncomfortable in the 150 even with the instructor in the right seat.

First flight lasted .8 hours, and we accomplished orentation, shallow turns, stability, and effects of flight controls. Over the next few months we added steep 720’s, slow flight, stalls, turns around a point, S-turns, emergencies, landings, (short field, soft field and normal).


At this point I want to talk about a training experience that still stands out. We were close to solo and were practicing takeoffs and landings. Turning base to final Jan got very upset at the way I was cross controlling the aircraft. Cross control is when you are in, say a left turn, and use opposite rudder to line the nose up with the runway. So, he had me depart the pattern and head east to the practice area, and climbing up to 5500 feet MSL, he had me slow down to just above stalling speed, start a left shallow turn and add right rudder. As the airplane stalled I had the strangest sensation, no roller coaster has ever come close, instead of blue sky in the windscreen I was looking at brown ground, and as far as I could tell we were upside down, through the terror of the moment Jan talked me out of the spin, controls neutral, oposite rudder, pull slowly out of the dive. As we leveled off he asked me what altitude we were at, as I remember it was around 2,800 feet MSL. Then he asked me what would happen if I experenced this on base to final in the traffic pattern. The answer was obvious, I would be a pile of wreckage off the end of the runway with a very short-lived aviation career. Needless to say this cured my cross-control tendencies.

Another training event the sticks out in my mind was the first time we did takeoffs and landings at the High School runway. The runway was 1,500 feet long, not sure of the width, but it seems like we had about 5 feet on each side of the wheels when on the center line of the runway. Landing from the south you also had to go between a cutout in the trees to be able to stop in time on the runway. After getting confortable landing here every runway since seemed huge. I remember landing at Chattanooga (KCHA) on a night cross country and commenting to Jan, that I felt like I could of landed sideways on the runway, it felt that large.

Very soon after this I started wearing old shirts to all my flight lessons, the reason for this occurred on February 8, 1978. The lesson that day was stalls, takeoffs and Landing. As we were taxing back in Jan told me it was time for my first solo. I was very excited, and after some last minute advice from Jan, including watch for floating on landing the plane will be light with him not in the right seat, complete 3 takeoffs and landings to a full stop. It was a blast, and at the end of my shirt was shorter in the back because Jan cut the tail out of it signed and dated my solo [an aviation tradition]. Total flight time accumulated on the day of my solo was 18.1 hours. I was now officially a pilot with solo priveleges.

In my next article I start cross country training, when Jan decided that it would be best accomplished this in the 172. Checking out in N5970R was like moving into a 747, this started a love affair with one of my faviriote planes to date. Since this time I have flown over 900 hours in many different models of the 172 and feel like I am stepping into an old friend every time.

More about Randy here: https://www.flyhpa.com/team/randy-delong/


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