A 100-hour inspection revealed four (of six) cracked bolt holes in the propeller spinner bulkhead (P/N 0552231-1). The mechanic suspects current propeller bolt torque values induce too much stress for the through-holes as bulkhead metal is formed into the chamfered area of the propeller bolt passages during torque.

His suggested correction would be a part redesign and/or heavier material for bulkhead manufacture. (This month’s SDRS submissions include identical defects in four additional 172’s. They will be added to the SDRS data base, which then will reflect an approximate 37 records of this model 172 aircraft defect since 1995.)

Part Total Time: 96.6 hours.