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I'm considering getting a private pilot license. From what I've read, pilot error is the leading cause of major airline crashes -- such as on this page, but that's for major commercial carriers. As the pilot, pilot error is something that I can address myself. One of the things that concerns me is the chance for an accident due to circumstances beyond my control.

What's the cause breakdown for general aviation accidents? What are the most common mechanical failures?

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For a statistical overview of General Aviation accidents I suggest checking out the Joseph T. Nall Report prepared by the AOPA Air Safety Institute. Everything I'm citing below comes from the most recent report (the 23rd report, covering 2011).

The leading causes of accidents in 2011 were:

  • Pilot Error - About 77%
    This includes poor flight planning, weather encounters, and a host of other things that we could at least theoretically avoid if we actually did the things we were taught to do in training.
  • Mechanical or Maintenance related - About 13%
    This includes engine failures, control system problems, landing gear failures, etc.
    • The largest chunk of mechanical failures are "powerplant failures", which account for 38% of the mechanical failures, or a bit under 5% of total accidents.
  • Everything Else - About 10%
    This includes freak occurrences like a flight instructor "walking into a moving propeller" (I kid you not, it's in the report!). A large chunk of these are also engine failure for causes that could not be determined.

If we add all the engine/powerplant failures together (the explainable ones from "Mechanical" plus the unexplained ones from "Everything Else") they come out to be 11.5% of total accidents, and are statistically the number two cause of Non-Commercial General Aviation accidents after "Pilot Error".

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  • $\begingroup$ The Nall report is fascinating reading. I ran across references before but they were dead links. $\endgroup$
    – AndrewS
    Aug 25, 2014 at 20:12
  • $\begingroup$ @AndrewS There are lots of other great resources on accidents if you poke around on the ASI site - the Nall report is pretty much the canonical compilation of that data though. Sadly not all of the years are available online, but also-sadly the reports are very similar year-to-year... $\endgroup$
    – voretaq7
    Aug 27, 2014 at 15:39
  • $\begingroup$ I wonder how many of those mechanical errors can be attributed to poor maintenance though. $\endgroup$
    – Jay Carr
    Aug 27, 2014 at 20:50
  • $\begingroup$ @JayCarr The way the Nall report is structured "maintenance-related failures" (ones caused by doing maintenance - either improperly or properly - and causing other stuff to break) and "maintenance-deferral failures" (caused by not doing maintenance) wind up in the same bucket - the concept of "provocative maintenance" is one that can be well applied to aviation though... $\endgroup$
    – voretaq7
    Aug 27, 2014 at 21:03
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Here is a good analysis that is a bit dated but should be relevant.

The data is from 1985-1995, 160,000 planes and 20,000,000 flight hours

Accident causes:
Pilot related: 80%
Mechanical/maintenance: 16%
Other: 2%
Unknown: 2%

The focus is mainly on pilot error (which is an interesting read). The breakdown of the mechanical/maintenance issues is as follows:

Engine/Prop: 70%
Gear/Brakes: 15%
Oil system: 5%
Controls/airframe: 2%
Fuel System: 3%
Electrical/Ignition: 3%
Vacuum Sys/Instruments: 2%

The NTSB has a lot of data available either in reports or by database query. The reports only break mechanical issues down to powerplant/non-powerplant. During 2007-2009 it was about 80% powerplant, 20% non-powerplant for personal flying. Other types of flying had various distributions. If you consider oil and fuel as powerplant systems, then it's about the same as the data above.

Anecdotally, from reading through many GA accident reports where maintenance was a factor, a lot of things come up after a maintenance visit. Things not attached properly/securely, not done correctly. So having good maintenance, and doing a very thorough check afterwards, will help.

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    $\begingroup$ Additionally for many mechanical failures the outcome depends on how good emergency plan the pilot has. $\endgroup$
    – Jan Hudec
    Aug 23, 2014 at 9:13
  • $\begingroup$ These are both great answers but I can only accept one... please leave this one up! $\endgroup$
    – AndrewS
    Aug 25, 2014 at 20:14
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My experience as a long time pilot and mechanic I have seen engine failures caused by accessories or other components external to the actual internal powerplant. If the powerplant is repaired or overhauled properly according to manufacturers recommendations and all the parts are approved and within tolerance the power plant can be expected to last until TBO. External components often fail much sooner than TBO. Items such as exhaust baffles blocking exhaust outlet, Magneto failure, starter drive coming apart, vacuum pump attachment failure, fuel pump failure, fuel injection or carburation problem, alternator failure and the list can go on. Preventive maintenance and detailed inspections can prevent failures.

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  • $\begingroup$ Good reminder that "engine failures" aren't always limited to just the engine itself. Welcome to Av.SE! $\endgroup$
    – Ralph J
    Jan 31, 2018 at 22:08

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