Unapproved Paint On Bleed Valve

(SDR) # 20110509010

SDR submitted:

The pilot was about to turn final westbound at 1500’ when a loud bang occurred followed by engine vibration and a continuous loud humming noise. The engine seemed to have rolled back to min fuel flow. The pilot manipulated the power lever and initially got no response. The pilot closed the power lever and engaged the emergency power lever which restored engine power. The pilot was able to land safely with the engine running at normal power and able to be fully controlled. From the initial bang, all the way to shut down, there was a loud continuous humming noise.

Post-incident, the bleed valve was removed and a small quantity of metal fragments was found in the bleed valve orifice. A teardown inspection confirmed paint applied by a repair vendor as an anti corrosion coating to internal bolts in the compressor bleed valve had chipped off one bolt. The chips plugged the internal orifice causing the bleed valve to close at low power settings initiating a compressor stall.

Transport Canada Comments:
This incident was traced back to one particular shop and the practice has ceased. We should all take it as a reminder that manufacturers’ instructions must always be followed. 

Cracked Engine Case

(SDR) # 20110523001

SDR submitted:

During troubleshooting of engine power issue, an 18 inch crack on the right hand side of the accessory gear case (magnesium housing), Time Since Overhaul (TSO):2119, was discovered. The crack extended approximately 180 degrees around the main diameter. This led to flexing of the engine case causing major internal rub damage to the rotating group and stationary components. The crack was found during trouble shooting of the engine running hot. The engine did not achieve target torque and was by-passing fuel at max Exhaust Gas Temperature.

The right hand side of an accessory gear housing showing an 18 inch crack

* The right hand side of an accessory gear housing showing an 18 inch crack

Transport Canada Comments:
It is possible that a previously installed engine truss assembly may not have been shimmed according to the Aircarft Maintenance Manual. This situation could create a stress loading on the engine case contributing to the crack. 

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