Let's discuss engine failures that have occurred following maintenance. This is another Aviation
Maintenance Safety Minute. We all know broken, or malfunctioning engine
controls are a significant cause of engine failure. This chart reflects 181 aircraft
accidents caused by engine maintenance issues. Cylinder torque and engine control cables
coming adrift were the top two maintenance induced accident causes closely followed by
loose B nuts and magneto parts coming adrift. Here's another common problem with engines.
This one here, the magneto shaft sheared off while in flight. If you look the way the thing
sheared off, it's kind of unusual, it's almost a polished edge.
I've never seen a mag fail like this, this engine was mounted on Diamond DA20C1 it's
our primary flight trainer. The pilot was at altitude talking to the controllers when
lost all power and oil pressure and they were able to direct him back here.
Made it back safety? He did make it back safety. Here is an example of a throttle cable disconnecting
in flight. August 27, 2018, about 37 minutes into the flight, the pilot noticed that the
engine manifold pressure was dropping, along with the airplane's airspeed, consistent with
a partial loss of engine power. The engine then experienced a total loss of power while
maneuvering for an emergency landing to a nearby airport. The airplane subsequently
landed short of the runway and sustained substantial damage to the aft fuselage.
Post-accident examination of the engine revealed that the throttle linkage had detached from
the throttle arm of the fuel injection servo. The rod end bearing for the linkage and the
throttle arm were intact and undamaged, but the connecting bolt and its associated washers,
castellated nut, and cotter pin were missing. It is likely that the bolt securing the linkage
had not been sufficiently tightened and secured with a cotter pin during the installation.
Who would think that a mis-installed clevis pin and cotter key could take down an aircraft?
It may not be normal that a landing with one or two operable engines could lead to a catastrophe
event, but it did. In this case, disregarding a special instruction from the manufacturer
started the chain of events that led to this accident. Fortunately, this was a good landing
in that everyone walked away. As seen in the video, the improperly installed clevis pin
(the mechanic turning it around from the manufacturer's instructions) led to the pin interfering
with other portions of the engine power controls. The airframe manufacturer was very specific
about that clevis pin, and it's orientation in the control system. The power setting for
the left engine could not be reduced below full climb power during flight, causing the
crew to shut it down and attempt a landing on one engine. The rest of the story had to
do with using thrust reverse on one engine...which did not end well.
The Nation Transportation Safety Board determined the probable causes for this accident to be:
The captain's failure to maintain directional control during landing with one engine inoperative.
Contributing to the accident was an improperly installed clevis pin in the left engine power
lever, the crew's delay in accurately identifying their heading, and their subsequent selection
of a runway with a strong crosswind. Inspections can generally reveal issues with engine controls.
Maintainers are required by 14 CFR part 43, Appendix D to inspect engine controls during
a 100 hour or Annual inspection, but are easily seen during a preflight inspection. Here's some
of the things you should check for;
Check for worn or fraying control cables a good way to see if a cable is coming apart
is to drag a rag down the cable and see if it catches on any frayed or broken strains.
Cotter keys missing, broken, or improperly installed.
Control linkage improperly installed or disconnected.
B-nuts not installed or loose or improperly installed.
Jam-nuts loose, make it a habit to physically try to turn them with your fingers to insure
they are properly tightened.
On your next preflight, take the extra time to look for the specific indicators that could
lead to a future engine failure. For the FAASTeam, I'm David Hays.