Piper PA-32 N8675N accident near Brunswick, Georgia

Probable cause

Maintenance personnel's failure to properly torque a No. 4 cylinder hold-down nut during engine overhaul, which resulted in the loosening of the nut and the subsequent failure of the studs and through bolts and separation of the cylinder.

NTSB analysis

The private pilot was conducting a personal cross-country flight. The pilot reported that the airplane was in cruise flight at 7,500 ft mean sea level when, without any warning, there was a loud explosion from the engine and an immediate loss of engine power. The explosion caused the oil filler door to open, and oil subsequently spewed over the windshield, and smoke filled the cockpit. The pilot declared an emergency and attempted to glide to a nearby airport; however, he landed the airplane on a rooftop a few hundred yards short of the runway.

Examination of the engine revealed that the No. 4 cylinder had separated from the engine case. All of the No.4 cylinder mounting stubs and through bolts were fractured except for the bottom forward stub; the nut for this stub was not located. The piston and corresponding connecting rod for the No. 4 cylinder were found in the bottom of the engine cowling.

A review of the engine maintenance logbooks revealed that the engine was overhauled almost 8 years before the accident and had accrued a total time of 1,005.0 hours since overhaul. There were no subsequent maintenance entries related to the No. 4 cylinder. Based on the evidence, it is likely that maintenance personnel applied insufficient torque to the cylinder's bottom forward hold-down nut, which allowed it to loosen over time. The stress load was then transferred to the remaining nuts, which resulted in the failure of the stubs and through bolts and to the separation of the No. 4 cylinder.

Text from the NTSB. Open the NTSB docket for ERA16LA071 for the full record.