As an engine manufacturer, we are often asked to guide pilots and mechanics concerning what to do about an engine after sudden stoppage, or a ground strike by the propeller. Service Bulletin No. 533 and Service Bulletin No. 475 state Textron Lycoming position concerning this problem. These important publications point out that there may be hidden internal engine damage from such an incident. From the experience of previous incidents, we know that the unseen damage to an engine by sudden stoppage or a hard ground strike has caused subsequent engine failures.
Some failures resulted from an over stressed crankshaft gear dowel which ultimately sheared. When this part breaks, all power is lost. Because of this, Textron Lycoming Service Bulletin No. 475 and AD Note 91-14-22 require a mandatory inspection, and compliance with repair and reassembly procedures.
In other cases, stoppage or ground strikes have resulted in over-stressed connecting rod bolts which failed soon thereafter. When a rod bolt fails, it allows the connecting rod to get loose and flail inside of the engine causing a nasty failure with a serious fire potential.
After a prop strike or sudden stoppage, the incident must be entered in the engine logbook. Textron Lycoming must take the position that in the case of sudden engine stoppage, propeller strike, or loss of a blade tip, the only safe procedure is to remove and disassemble the engine and completely inspect the reciprocating and rotating parts. This will require a skilled mechanic who knows what to look for in the affected engine.
Any decision to operate an engine which was involved in sudden stoppage, propeller strike, or loss of prop blade tip without disassembly and inspection will violate the AD Note issued by the FAA and Lycoming Service Bulletin No. 475, both of which are mandatory. Any decision to fly an engine without complying with these publications must be the responsibility of the agency returning the aircraft to service.