23 Dec. 2012
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Mostly Bad Luck?

Almost two years ago I had the unhappiness to report on the death of my friend Bruce Jackson in the crash of his Mooney aircraft.  He was the pilot and the sole occupant, so there was nobody to ask "What happened?"  In my remembrance of Bruce I mentioned that speculation about accident causes is often pointless, and offered the conventional wisdom:

Aircraft accidents rarely have a single cause.  Usually some chain of events conspires to cause the airplane and/or occupants to meet an untimely end, and these causal chains often begin with something subtle.

The reason that this is "conventional wisdom" is that it is usually correct, and it was essentially so in this case.  In this blogitem you get three summaries, mine, a slightly abridged National Transportation Safety Board narrative, and, if you click on the report number, even more detail.  You also get something of a puzzle.

So, What Happened?

Today I received an unexpected email from John Bell with a copy of the NTSB report quoted below.  This is the first I was aware that an updated report had been issued. It's dated about six weeks ago.

According to the NTSB, the engine partially lost power due to poorly fastened magneto clamps.  It's not clear just how "partial" the power loss may have been.  They then mention the terrain on which the airplane crashed, which was "unsuitable for making a successful off-field landing."  Their "probable cause," which will be considered the reason for the crash, was the sequence of these two issues:  Engine power loss followed by landing on an unsuitable surface, which caused multiple traumatic injuries which were the cause of death.  In other words, if the engine hadn't lost power, all would have been fine.  And, if the engine had failed but there was a "suitable" landing area, the crash would have been survivable.  (This is not unlikely, by the way.  Loss of engine power in a fixed wing aircraft usually results in a survivable accident, and not infrequently a repairable airplane.)

And there you have it.  Bruce died due to a mechanical failure of his aircraft and the bad luck of being over craggy terrain. 


There you don't have it.  Reading the summary report below, the above scenario is believable.  Reading the complete report, you find a paragraph that seems to me totally incompatible with the summary.  It is this:

The airplane appeared to have collided with level terrain in a slightly left bank, nose low attitude. The flaps and landing gear were retracted. The throttle, propeller, and mixture controls were full forward.

First, note that he took off, according to witnesses, in mid-afternoon.  Since the crash occurred just seven miles from the airport, it almost certainly occurred in mid afternoon.  In other words, there was plenty of daylight and the terrain would have been clearly visible.  Next, the crash occurred while the engine was operating.  At some point, assuming the engine wasn't developing nearly enough power to get back to the airport, the pilot would realize that and his goal would be to try to survive the crash.  The best way to do that is to keep control of the aircraft and hit the ground as slowly as possible.  You do that with a nose-high attitude, the throttle fully retarded, and flaps deployed to be able to fly slowly.  But, see the quoted paragraph!

So what really happened?  The aircraft lost some power shortly after takeoff.  A partial power loss isn't necessarily an emergency.  If the cause, such as carburetor icing, isn't obvious and fixable, you can turn around and try to land at an airport if there is one close at hand, but there's no evidence in the report that Bruce did that although he was close to the airport.  Also, if it becomes apparent that you can't make it as far as the airport, you prepare to crash by reducing your airspeed, which it also appears he did not do.  So what happened (or didn't happen) between the time he lost partial power and the time of the crash?  Or:  What if he did NOT lose partial power?  Clearly the engine was running when the crash occurred.  Perhaps there was no sudden diminution of power, which is consistent with his continuing on course as implied by the direction of the crash? 

Good questions, I believe, and questions not answered or even hinted at in the NTSB report.  I should point out that the NTSB is staffed by government experts who have vast experience investigating aircraft crashes.  I am a not especially experienced pilot with no advanced ratings and no experience in investigating or interpreting either crash scenes or the reports they engender.  Most people who believe they have found significant anomalies in official reports at least make an attempt to claim expertise and try to convince you that they are right and the report is wrong.  I am not one of them.  I claim a lack of expertise, and I would prefer to believe that the NTSB report is essentially correct.

NTSB Summary Report on Bruce Jackson's Aircraft Accident

(Slightly edited to remove non-germane boilerplate.)

NTSB Identification: WPR11FA114
Accident occurred Saturday, January 29, 2011 in Furnace Creek, CA
Probable Cause Approval Date: 11/05/2012
Aircraft: MOONEY M20J, registration: N50BJ
Injuries: 1 Fatal.

A witness reported observing the airplane take off to the south and stated that the ground operations and takeoff appeared to be normal. The wreckage was located 2 days later on a flat, dry salt lake bed 7 miles south of the departure airport. The surface of the ground was deep jagged salt deposits, with crevasses between 6 and 18 inches deep, and unsuitable for making a successful off-field landing.

During the postaccident engine examination, the single-drive dual magneto was found mounted on the accessory pad and could be easily rotated by hand. The magneto had sustained no apparent impact damage and remained in good condition externally. Further examination of the attachment hardware found all required mounting studs, lock washers, and respective nuts to be in place and undamaged. The magneto clamps, respective magneto flange, and the accessory case interface areas exhibited wear signatures consistent with fretting, which suggested that the clamps were not securely fastened. These signatures were most prominent on the lower clamps and flange area. The magneto flange remained intact and revealed no evidence of cracking. It is likely that this could have produced a partial power loss, which led to the pilotís decision to make an off-airport landing. No other mechanical failures or malfunctions were found that would have precluded normal operation. The airplane had accumulated about 10 hours since the last annual inspection. No maintenance records were located to determine if further maintenance had been performed on the engine since the inspection 5 months prior to the accident.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The magneto clamps were not securely fastened to the mount, which led to a partial loss of engine power and a subsequent forced landing on unsuitable terrain.

"The Angels' Share"
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