Catastrophic Engine Failure - Piper Seneca II

[Avidflyer2]

Before anyone becomes excited - No injuries, no damage to any other part of the airplane!

Piper Seneca II with TSIO-360-EB engines, #2 Cylinder connecting rod failure.

This occurred near the end of a ATP checkride during a go-around. The airplane reached an altitude of about 500 feet when the crew heard a slight "knock" in the engine. Moments later the "big bang" occurred - no problems with oil pressure or temperature. Crew immediately feathered and shut down the left engine and returned to land at the departure airport using a teardrop pattern landing downwind. Oddly enough, the crew immediately took up another airplane and finished the checkride!

The connecting rod nut was found lodged in the baffling outside of the engine crankcase. The nut exhibits some hammering and the threads are slightly worn, but I wouldn't say completely stripped. The rod bolt is covered up so I cannot tell if the rod bolt is stripped or not. The connecting rod journal on the crankshaft appears to be in good shape so it is not a lack of lubrication problem. Nothing inside of the cylinder or combustion chamber indicates a piston seizure or valve problem either. Everything so far indicates the connecting rod nut either loosened or was stripped off of the rod bolt. The connecting rod is broken about an inch up from the rod bearing journal at the crankshaft end. The connecting rod small end is still attached to the piston pin - no damage there. Pieces of the piston's scraper ring were found in and outside of the crankcase. (The piston is also beaten up pretty badly.) The connecting rod also struck and broke the camshaft into two pieces. There is damage to the two counterweights or torsional dampers attached to the crankshaft, but the crankshaft appears to be unhurt. Maybe a few parts like a few cylinders can be salvaged from this engine to reduce the cost of a repair or overhaul. Luckily we have a running spare with which to reduce the downtime to get this airplane back into the air. It may be a few weeks before any decision is made what to do with this badly damaged core.

I'm thinking repeated overspeeds and or fatigue failure of the connecting rod bolt precipitated the connecting rod failure which then "all hell broke loose". Connecting rod failures are pretty rare but I cannot completely discount fatique failure of connecting rod "H" section. What do you think?

 

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