On April 14, 1989, a DE Havilland DHC-6-100 (registration N100AP) was involved in an aviation accident near Barrow, AK. Investigators recorded the probable cause as: A fatigue fractured elevator bellcrank mounting quadrant, P/N C6CFM1142-1, resulting in a complete loss of elevator control. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
After departure, the control yoke was pulled forward out of the captain's hands, causing a pitch-up. The crew regained control using power adjustments and returned for a safe landing. Inspection revealed a fatigue-fractured elevator bellcrank mounting quadrant.
Incident Description
The airplane had just departed from Barrow, Alaska, on a scheduled commuter flight with five passengers and two crew members on board. Upon reaching an altitude of 150 feet above ground level, the control yoke was pulled forward out of the captain's hands and pinned against the control panel. Simultaneously, the nose of the airplane suddenly pitched up 60 degrees above the horizon. The captain reduced power, causing the nose to pitch 30 degrees below the horizon. The flight crew was eventually able to maintain a level attitude by power adjustments alone and returned for a safe landing.
Inspection Findings
Inspection of the aircraft revealed a fatigue fractured elevator bellcrank mounting quadrant, part number C6CFM1142-1, resulting in a complete loss of elevator control. The elevator bellcrank mounting quadrant had been in service since 1966 and had accumulated 17,826 operating hours. The fracture occurred between the vertical stabilizer stub fin attachment bulkhead and the bellcrank.
Metallurgical Examination
Metallurgical examination of the fracture revealed multiple fatigue origins in the vicinity of superficial machining abrasions.
Probable cause
A fatigue fractured elevator bellcrank mounting quadrant, P/N C6CFM1142-1, resulting in a complete loss of elevator control.