Raytheon Aircraft Company A36 N3241N accident near Fayetteville, North Carolina

Probable cause

Maintenance personnel's application of an unapproved sealant to the engine case halves during engine overhaul, contrary to manufacturer's instructions, which resulted in lubrication restriction due to a bearing shift and the subsequent internal failure of the engine due to the loss of case through-bolt torque.

NTSB analysis

During a cross-country flight at night, the airplane experienced a total loss of engine power. The private pilot's attempts to restart the engine were unsuccessful. The pilot attempted to glide the airplane to a diversionary airport, but when he realized the airplane would not reach the airport, he conducted a forced landing into wooded terrain.

Teardown examination of the engine revealed that the No. 1 cylinder and No. 3 connecting rod had fractured. Metallurgical examination revealed that there was a gray rubbery substance on the case halves, through bolts, and main bearing saddle faces, which could have restricted oil flow. The engine manufacturer's overhaul manual and a service bulletin and service information letter (SIL) listed only one approved sealant for use between case halves, which was similar in color and texture to grape jelly not to the rubbery gray sealant found in the engine, which was not an approved sealant. Further, the SIL stated that the use of an incorrect sealant "on mating threads and between mating surfaces can cause incorrect torque application and subsequent engine damage or failure."

Further, the No. 3 connecting rod journal exhibited heat damage and deformation, and the No. 3 connecting rod fracture was consistent with a lack of lubrication. Additionally, the No. 4 main bearing saddle boss exhibited fretting damage, consistent with bearing shift due to lack of torque on the through bolts and blockage of its oil port, which also would have restricted oil flow.

Review of maintenance records revealed that the engine was overhauled about 20 months before the accident. The engine had been operated for about 300 hours during that time. It is likely that maintenance personnel applied the unapproved sealant to the engine case halves during the engine overhaul, which ultimately resulted in the total loss of engine power.

Text from the NTSB. Open the NTSB docket for ERA16LA066 for the full record.