The Nigeria Accident Investigation Bureau (AIB) has issued a preliminary report on the fatal crash of a Sikorsky S-76 helicopter operated by Bristow Helicopters in Lagos.
The accident occurred on Aug. 12, 2015, as the S-76C+ was returning to Murtala Muhammed Airport in Lagos from an offshore oil rig. Shortly before arriving at the airport, the helicopter crashed into a lagoon in the Oworonshoki area of Lagos, killing the two pilots and four of 10 passengers on board the aircraft. The remaining six passengers were seriously injured.
According to the preliminary report, flight recorder data retrieved after the crash indicated that, at an altitude of 1,000 feet and an airspeed of 120 knots, the helicopter experienced a sudden pitch up and left roll with varying attitudes of yaw, roll, and pitch for 12 seconds until it impacted the water.
The preliminary investigation into the accident revealed that the aircraft’s forward main servo input control pushrod assembly had failed, with the control pushrod tube separating from the control rod end with the bearing and jamnut. According to the report, the jamnut was loose and was not seating against the control rod. U.S. National Transportation Safety Board preliminary metallurgical examination revealed that the separation was a pre-impact condition.
The report notes that, in response to the findings, the U.S. Federal Aviation Administration on Sept. 14 issued an emergency airworthiness directive (AD) to all S-76 operators requiring inspection of the main rotor forward, aft, and lateral pushrod assemblies, the tail rotor pushrod assembly, and the jamnuts, and applying slippage marks across the pushrod tubes and jamnuts. The emergency AD followed the issuance of an alert service bulletin from Sikorsky Aircraft Corp. on Sept. 10.
The report also notes that the aircraft’s No. 2 engine appears to have suffered an uncontained failure. The complete report is available on the AIB website.
