“Over The Airwaves” and the GA Fatal Accident Rate

Posted by in Safety

Many of us in the aviation world have recently come to know the name Robert Miller.  Mr. Miller is an east coast CFI and the author of Over the Airwaves.  OTA’s masthead describes it as “the bi-weekly journal for the proficient pilot”.

I’ve been reading Over the Airwaves for about a year and find that I agree with Mr. Miller on many points.  He’s obviously dedicated to the issue of flight safety and a proponent of realistic, recurrent training which exceeds the Practical Test Standards and embraces the real-world aspects of flying.

I continue to read OTA and learn a lot from it.  And I should note that his dedication to publishing Over the Airwaves is admirable.  One can’t help but stand in awe of the many hours it must take to put together each issue.  I commend him for venturing beyond the traditional CFI methods of providing information to pilots and hope he continues to publish OTA for a long time.

Having said that, I’ve noticed that OTA seems to spawn from a single raison d’etre, namely that the general aviation fatal accident rate is “worsening at an alarming rate” (OTA Vol. 3, No. 25).  Statistics, tables, and charts are proffered in support of this thesis, and I must admit the case looks compelling.  It begs the question:  have AOPA, the Air Safety Foundation, the FAA, and the NTSB been lying to us?  Are they glossing over the true story on general aviation flight safety?

I decided to look into this issue a little deeper, not to discredit Mr. Miller or his publication — remember, I’m an avid reader of Over the Airwaves - but because for some reason his theory just didn’t feel right.

I began by asking him where he got the raw data to support the claim that “We are marching down seven straight years of worsening GA fatal accident rates”, because the data I see from the Air Safety Foundation and NTSB suggest that the fatal accident rate has been in a long term hold.  In light of the fact that annual GA flight hours are estimated, the NTSB figures showing a rate hovering near 1.3 per 100,000 hours for the past decade indicate that GA fataility rates are not getting worse.  My source:  http://www.ntsb.gov/aviation/Table10.htm

Bob very kindly replied and referred me to the headline article in Volume 3, Issue 23a of OTA.  This article uses avgas sales to suggest declining flying activity.  He also pointed me to a linear regression analysis at the bottom of Volume 3, Issue 25 which suggests an increasing fatal accident rate:

After reviewing the data, I still suggest that his analysis is quite flawed.  Miller ties avgas burned to hours flown.  To be fair, the NTSB uses the same methodology.  However, the connection between the two cannot be a direct one, because the Department of Energy stats he references would then indicate that flying activity has declined 80% since 1983.  The table shows a drop from 418,000 gallons/day in 1983 to 98,000 gallons/day in 2004.

A more logical explanation is that there are various reasons for the drop in avgas fuel usage:

  • Let’s begin with the pilot popuation.  Yes, there are fewer pilots flying today than there were in the 1980s.  I don’t really care how many are in the FAA registry.  Many of them don’t fly anyway, just as they didn’t fly in the 80s.  But the number of active pilots is down, maybe 10% I’d estimate.  Even if it’s higher, there’s no way it would come close to an 80% drop.

 

  • There are fewer piston twins flying today than there were in 1983.  Who is even making piston twins these days?  The Baron, Seminole, and TwinStar sales combined total fewer than 50 airplanes per year.  Cessna is completely out of the piston twin market, and for the most part so is Piper.  No more 300 and 400 series twins, no more Twin Comanches, Apaches, Aztecs, Twin Bonanzas.  You name a piston twin, it’s pretty much been out of production for decades.  And the existing piston twin fleet is being decimated by the inevitable ravages of time, spar ADs, high operating costs, limited parts supplies, and so on.  Fewer twins flying = lower total fuel consumption per hour flown.

 

  • Single engine airplanes are more efficient.  An SR20, SR22, DA20, DA40, Columbia, or other modern airplane gets far better economy than the airplanes of the 80s.  Composite construction and advanced aerodynamics allow these planes to fly with less drag.  Any decent MFD or GPS can show you the real time NMPG efficiency of that airplane.  Especially at lean of peak operation, these planes burn a fraction of the fuel a piston twin does.

 

  • Now, consider lean-of-peak operation.  Advanced engine monitoring and fuel metering for GA has led to greater use of fuel efficient operating techniques.  We care about fuel burn now because fuel is expensive.  Even without an engine monitor, nobody goes flying around with the red knob all the way in for hours on end.  In my Pitts, I can burn anywhere between 11 and 26 gph.  Considering that I only have 23 gallons of fuel on board when I takeoff, that’s not irrelevant data.

 

  • But the biggest factor in the decline of avgas since the early 80s is the nearly 100% decline in piston twin usage by commercial operators since 1983.  The commercial operators used to fly piston airliners for freight delivery, and GA piston twins for smaller stuff.  Corporate operators used to fly executives around in piston twins, whereas nowadays nearly all those folks have moved up to turbine twins and/or jets.  The corporate/commercial operators flew a huge chunk of the total piston hours in the early 80s.  Over time, they moved to turbine equipment and therefore bought less and less avgas.

 

  • Look at the DOE statistics for jet fuel usage.  They show a 65% increase in jet fuel consumption over the same period that avgas dropped by 80%. During that same period, the total U.S. civil fleet has remained consistent in numbers, ~200,000 aircraft on the registry.

OTA’s fatal accident rate per million gallons of avgas consumed analysis is also flawed, because the GA accident rate includes all sorts of general aviation airplanes, and as previously noted, a great portion of GA flight hours are now being accumulated in aircraft with turbine rather than piston engines.

In regards to Mr. Miller’s linear regression table at http://overtheairwaves.com/vol3-215.gif, it is also deceptive.  It uses too few data points to be statistically relevant.  Increase the data to include numbers going back to 1983, as he did with avgas, and it would show a different picture, namely a) a long term decline in accident rates, and b) that the chart’s vertical axis only represents 0.14/100,000.  Zoom in far enough and you can make anything look bad just by virtue of the chart’s scale.

Even given the data as Mr. Miller presents it, there exists a variance between a fatal accident rate of 1.25 and 1.32 per 100,000 hours flown.  Think about that.  For every 100,000 hours flown, the accident rate went from 1.25 to 1.32.  That’s an increase of 0.07 accidents per 100,000 hours.  To put it another way, it’s an increase of 5%, which to be honest is probably less than the margin of error when you consider that the hours flown are merely an estimate.

OTA describes this as “worsening at an alarming rate”.  Am I crazy for disagreeing?

As I said before, my analysis is not designed to slight Mr. Miller or his publication.  I simply suggest that he is trying to have it both ways with the statistics.  He claims that the NTSB’s “hours flown” esimates are way off because of the decline in avgas usage, yet uses those same NTSB numbers for his regression analysis.

These are just one guy’s thoughts on the matter.  But from where I sit, the accident rate is holding steady over the past few years, and remains in a long term decline.