Lessons Learned. Episode #4 - Flight controls misrigging after maintenance. ⠀

Great post! Rigging is considered a critical task as far as maintenance is concerned and should require (at the very least) a double check. It would be interesting to see exactly what failed in that process validation. Do you have any further info about this case?

Hi FTE!

The case was investigated by the NTSB and conclusions were clear: human error.

The senior mechanic (24 years experience) misrigged the trim. He was interviewed afterwards to try to understand and the system and avoid future occurences, he said "When I heard the I had misrigged it, I was in disbelief". He couldn't believe it when he found where the control cables had done a 180º when they were put on the actuator.

This is human error, it does happen, can happen to anyone, we just need to continue focusing on how to mitigate its consequences. Despite his human mistake the mechanic showed a lot of courage admitting his mistake and collaborating publicly with the NTSB to put in new methods to fight against human error.

Thanks for sharing this. Not just a GA issue... whats wrong with this picture??

Hi Marc. Thanks for answering. Was this in the US (NTSB reference)?
I am asking because in EASA it wouldn't be down to just one person - an engineer can always make a mistake, but in critical systems (like rigging) there is always a check from an independent person to make sure maintenance was done properly. That is why I asked initially what failed in the validation process.
Thanks!

The failure was on the part of the pilot for not checking the correct operation of all flight controls including the trim before taking the aircraft on a test flight.
About 40 years ago in Australia some friends of mine were involved in an accident with a Libelle sailplane where the ailerons were rigged backwards resulting in the destruction of the aircraft on takeoff. Fortunately no injuries. The maintainer got it wrong, the person who assembled the glider out of the trailer obviously didn't check and the test pilot (another person) obviously didn't do his pre-flight control check properly. Another couple of inspectors looked at the wreckage on the runway and couldn't see what was wrong. The third one did. A dual check simply isn't a guarantee that all is well.
The Glasflugel aileron drive system assembles and works just fine when left and right drives are swapped, just in the wrong sense.
That failure mode wasn't known at the time.

The failure finally was lack of proper pre-flight discipline on the test pilot's part..
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About 25 years later in NZ I was sitting in line in a PW-5 waiting for a tow and the guy in front was in a Libelle. The wing dropped on takeoff and he aborted the launch. Had another go - same result. By now I was unstrapping and asked if he was going to try again. He said he'd have a think about what might be wrong. I asked if the aircraft had just had maintenance. Yes! We walked over to it and I demonstrated that the ailerons operated backwards.

Wow Eyrie, thank you very much for sharing this. You are right it is the pilot's responsibility to check control surfaces movement as part of any preflight check, but you will agree with me that reverse trim is a tricky one to catch. Especially because your brain expects to see movement, and trimming a Cessna wheel downwards and seeing the trim tab moving downwards as well isn't something your brain will catch easily unless you take it really slow and train your brain on red flags when this happens. But this is what the episode is all about, Maintenace=danger, Just triple check everything as u well say. Again, thanks for sharing your experience, I am sure many of us will benefit from it.