Tuesday, September 22, 2015
S-76 Crash Probe Highlights Control Failure
Sikorsky Aircraft S-76 operators have inspected their aircraft for control-system discrepancies implicated in an Aug. 12 Bristow Helicopters crash that killed six people near Lagos, Nigeria. The inspections came in response to a Sept. 14 FAA emergency airworthiness directive that ordered inspections with 5 hr time in service of main-rotor and tail-rotor servo input control pushrod assemblies on all S-76 models. (That directive followed a Sept. 10 Sikorsky alert service bulletin.) Nigeria's Accident Investigation Bureau is still probing the crash of the Bristow S-76C+ into the Lagoon off Oworonshoki while on approach to Runway 18L to Lagos' Murtala Muhammed Airport and has not reached a final finding of causes. But its preliminary report said the aircraft's forward main servo input control pushrod assembly was found to have failed, with the control pushrod tube separated from the end of the control rod. The FAA said control-rod failure could cause loss of main- or tail-rotor control and subsequent loss of control of the helicopter. Nigeria's review of the aircraft's solid-state combined cockpit voice/flight data recorder, conducted with the U.K. Air Accident Investigation Branch and the U.S. NTSB, found that a pilot acknowledged the air traffic controller's instruction to report the left downwind for the runway at 3:30 p.m. local time, but made no further radio transmission. The investigation bureau said the flight data recorder indicated that, while at 1,000 ft and 120 kt, the S-76 pitched up suddenly and rolled left "with varying attitude of yaw, roll and pitch for 12 seconds." It hit the water at about 3:31 p.m. local time. The S-76 was carrying 10 passengers from the Sedco Express offshore flight. The crash killed both pilots and four passengers. The flight to the rig was uneventful, the accident bureau said, and no life vest or raft on board the aircraft had been inflated. The crash killed both pilots and four passengers.