Sunday, July 27, 2008

Prop strike teardown recommendation

To answer the question "should the engine have been torn down for a more complete inspection"?

My recommendation has always been to do a tear down inspection for the following reasons:

1. After a prop strike there is rightful concern about the airworthiness of the engine. This concern can only be answered by inspection and not by hope, prayer, or opinion.

2. Having a shop that has performed approximately 1 prop strike inspection each month for some 20 years, I still cannot tell you which prop strikes cause damage and which ones don't without an inspection. This has taught me that the preceived "severity" of the propeller strike is not a criteria for deciding which engines should be inspected and which ones need no inspection.

3. I personally didn't tear down my engine after I hit the towbar with the propeller and sent it flying across the airport. But then we did one on a Navajo that hit a plastic caution cone that had damage -

4. Engine mounts can also be damaged. That said, my opinion is based on my personal experience and others have views that conflict with mine based on their experience and judgement. I could be wrong.

I have spend many year pondering how to inspect the engine without tearing it down and I have never come up with an adequate method. Your question as to signs to look for - I don't know.

The pilot and his single passenger were fatally injured Cessna 210L, N5060V  "The crankshaft contained a fracture that intersected the aft fillet radius for the propeller flange and the cylindrical portion of the crankshaft located aft of the aft fillet radius."

"According to an airplane mechanic who had worked on the accident airplane,N5060V had been involved in a propeller strike incident in which the propeller was damaged. The propeller was removed and sent for an inspection and overhaul. The mechanic reported, "The owner of Gallatin Flying Service, [name of owner], was  informed and advised of the need to do a teardown of the engine to check for damage. He would not approve doing this. We [the maintenance staff] did a run out check on the  crankshaft, aft of the propeller flange, with a dial indicator. No defects where noted at that time."

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