shear bolts

[happygolucky]

perhaps for engineers, how serious is it if a shear bolt is left of a engine after engine change :rolleyes:

[mono]

Seems a bit of an odd question.

There are not any shear bolts removed/replaced during an engine change (not on the a/c I work on). Most engines are held in place with cone bolts which are changed (or at least NDT checked) when the new engine is installed.

The shear bolts are part of the pylon installation and won't be touched on an engine change.

I would seriously doubt the integrity of a pylon installation with missing shear bolts, and have been involved in replacing bolts which have become mearly damaged due ground vehicle collisions.

[lomapaseo]

in my mind, one can define just about any bolt as a shear bolt, so I really have no idea what the original poster is talking about.

All the bolts holding the engine and the pylon are designed to withstand all anticipated rigours of engine failures and in-flight gust loads. It is true however that some gust loads and accompanied aerodynamic loads on the wing can break aircraft wings or other critical structures.

The idea is to make sure that any such aerodynamic loads imposed on the lesser critical pylon (not actually needed for flight) will not break the wing (which is always needed for safe landing). Thus some bolts are designed to be weaker than others.

With that said all such loads are designed to be used in a redundant system which provides many parrell paths to carry these loads so that if any path is broken there will still be plenty of margin for normal flight loads.

The history has many examples of broken or missing bolts in the engine mount pylon system and then sustaining some pretty massive engine failures loads without any cause for alarm..

Of course their is always a limit to our immagination of just how many missing bolts does anybody expect to dispatch with.

[tinyrice]

I can tell you what happens if you leave a pylon fuse pin ( shear bolt ) out after a pylon drop. Ten landings later, the remaining fuse pins fail,and the front end of the pylon/engine pivots forward around the aft attach to contact the runway in a shower of sparks and debris. Thankfully it happened on the runway in reverse and not moments earlier on short final.

[lomapaseo]

"I can tell you what happens if you leave a pylon fuse pin ( shear bolt ) out after a pylon drop. Ten landings later, the remaining fuse pins fail,and the front end of the pylon/engine pivots forward around the aft attach to contact the runway in a shower of sparks and debris. Thankfully it happened on the runway in reverse and not moments earlier on short final."

They left a lot more out than a single fuse pin on that incident and it did survive several flights until it got a bad jolt on the ground.