Missing cotter pin brings down Luscombe

Aircraft: Luscombe 8A. Injuries: 1 Fatal, 1 Serious. Location: Dixie, Ga. Aircraft damage: Substantial.

What reportedly happened: While the airplane was in cruise flight, the pilot noticed the engine oil temperature rising.

He reduced power and headed toward the nearest airport. The airplane was four miles from the destination at an altitude of about 1,000 feet AGL when the engine experienced a catastrophic failure. The airplane collided with two trees during the forced landing.

The post-accident examination revealed that the No. 2 cylinder piston connecting rod had separated from the crankshaft. One of the bolts securing the rod cap was missing. The bolt and nut were recovered from internal engine debris, however a safety cotter pin necessary to secure the bolt was not located.

About 20 engine-operating hours before the accident, all of the engine’s piston connecting rod bearings and their respective bolts and nuts had been replaced. Investigators determined that it was likely that at that time one of the two nuts was not properly secured with a cotter pin on the No. 2 cylinder piston connecting rod, allowing the nuts to slowly unthread over time.

Probable cause: Maintenance personnel’s improper installation of the No. 2 cylinder’s connecting rod, which resulted in the disconnection of the rod and a subsequent loss of engine power.

NTSB Identification: ERA12FA017

This October 2011 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.

 

Comments

  1. No cotter keys on my Lycoming, but my buddy had his O-360 conn-rod bolts fail due to a misapplication. When you tightened the bolts, there was less threads securing the rod cap!

    Luckily, the right bolts work, and the rods are reliable.

    Funny how all the regs and rules failed to prevent the problem, and the certified shop was trusted on paper.

    It caused him a dead stick, luckily he never left the pattern, in his flying that day!

  2. vaughn S. Price says:

    Tom & Jim have it right
    If you believe an engine won’t quit you are in a fools paradise. I teach my students to at all times have the best available emergency landing field picked, even if its over a dense forest.
    Pick two big trees and go between them shearing the wings off. Even stalling high over a tennis court is preferable to hitting a building. Engines quit. get your head out of the clouds, and be alert

  3. We can expect more problems like this with the ECI cylinder AD. Miss-aligned bearings are more likely than not having things saftied, bu,t opening up a working proven ,( a few hundred hour,200+), engine is not a good idea. Infant mortality of engines is common and not always traceable to a single cause, it some times “just happens”. Mechanics try very hard to always do things properly, sometimes they make mistakes sometimes parts fail, sometimes who knows?

  4. Craig a cotter pin can not unbend, A toothpick could hold a nut in place, there simply is no strain on a cotter pin. In a case such as this it is the mechanics fault. There is not way that a cotter pin, properly put into place could fail in a situation like this.

  5. I just hate to see when the NTSB could not find a cotter pin it must have been the mechanics fault. I don’t care if they call it “Probable Cause” there was nothing conclusive about the situation but lets lay it on the mechanics. Maybe somehow the cotter pins metal was not up to snuff and easily “un bent” through vibration and slipped out. I know, far fetched, but it could happen. Maybe leaving it as a mechanical fastener was to blame would have been a better probable cause.

  6. We place profound trust in our mechanics to do their jobs perfectly. When they don’t, catastrophe can result. That’s why we should fly with the awareness that, at any moment, the engine could quit or the aircraft could malfunction. Always have an “out” in mind. And keep your fingers crossed. The folks with the tools are only human.

    • Thank you Tom! If a man built it, it will fail eventually, so pilots should always keep that in the back of their minds. If you rely on that old A65 to keep you alive 100% of the time, it will let you down. Always give yourself a way out, and don’t blame the mechanics when you stick an exhause valve while you were wheel skiing on the lake!

Speak Your Mind

*