Robinson Helicopter R44 N44EK accident near Chatham, New Jersey

Probable cause

Maintenance personnel's improper installation and inspection of the crankshaft gear bolt during major overhaul, which resulted in the crankshaft gear disengaging from the accessory gears of the engine and a subsequent loss of power.

NTSB analysis

The private pilot was on the second leg of a cross-country flight in the helicopter. After about 45 minutes and while in cruise flight at 1,800 ft mean sea level, the engine lost total power; the low rpm warning sounded, and the pilot initiated an autorotation in the congested area during nighttime conditions. During the autorotation, the helicopter struck a building, which resulted in substantial damage to the fuselage. Postaccident examination of the engine revealed that the crankshaft gear bolt was about 3/16 inch from the seated position. The safety lockplate washer was worn, the back of the bolt head displayed rotational scoring, the bottom threads of the bolt were damaged, and the alignment dowel had sheared. The engine had accumulated 5.9 hours total time since undergoing major overhaul about 1 year before the accident. It is likely that, when the engine was overhauled, the crankshaft gear bolt was not properly seated against the gear, which resulted in the crankshaft gear disengaging from the accessory gears and a subsequent total loss of engine power.

Text from the NTSB. Open the NTSB docket for ERA17LA116 for the full record.