Beech F33A N85WM accident near Sanford, North Carolina

Probable cause

A loss of electrical power as a result of broken stator leads within the alternator, which resulted in the pilot’s inability to extend the airplane’s landing gear.

NTSB analysis

The pilot reported that after practicing instrument approaches with the flight instructor, they were returning to the airport. While in the traffic pattern, the pilot lowered the flaps with no problems noted, but as he attempted to lower the landing gear, the airplane lost electrical power. The pilot performed a low pass of the airport and reported that individuals on the ground confirmed that the landing gear were down, but they were unsure if they were in the locked position. The pilot then attempted to lower the landing gear with the hand crank, and he managed to make about 20 total turns (of about 50 normally needed to fully extend the landing gear) before he was unable to turn the crank any further. During the subsequent landing, the nose landing gear collapsed and the airplane sustained substantial damage to the lower fuselage.

Postaccident examination flight data recovered from avionics onboard the airplane revealed that shortly after departing on the accident flight, current parameter indicated a discharge from the battery for the remainder of the flight and electrical bus voltage began to slowly decrease. A postaccident examination and functional test of the alternator revealed that the case halves of the alternator had vibrated apart and that the alternator had was not functioning. It was disassembled and the stator leads were found to be broken at the rectifier attachment point.

Text from the NTSB. Open the NTSB docket for ERA26LA191 for the full record.