On the 3rd of February, 2016, Accident Investigation Bureau was notified of the accident by the Nigerian Civil Aviation Authority through a phone call and investigation commenced same day. All relevant stakeholders were notified.
A Sikorsky S76 C++ helicopter with nationality and registration marks 5N-BQJ, a domestic charter flight operated by Bristow Helicopters Nigeria Ltd departed Murtala Muhammed Airport Lagos (DNMM) with 11 passengers and 2 crew for Erha Floating Production Storage Off loading (FPSO) helideck. The Captain was the Pilot Flying (PF) while the First Officer was Pilot Monitoring (PM) on this leg of the flight.
The take-off and climb-out was normal. A few minutes into the flight, the Captain observed an unusual vibration of the aircraft and made a remark about this to the First Officer. About fifteen minutes later, the crew also reported that the Digital Auto Flight Control system (DAFCS) and TRIM FAIL lights illuminated twice and were reset. The No.1 autopilot decoupled on both occasions. Also, according to the PM, a passenger seated in the middle row reported perceiving a burning smell. However, the aircraft continued to destination and landed. On ground Erha, the Captain conducted visual checks but could not ascertain the source of the burning smell earlier reported.
Instrument Meteorological Conditions prevailed at the time and Instrument Flight Rules (IFR) flight plan was filed.
At 09:50 h, 5N-BQJ departed Erha FPSO for Lagos on the second leg of the flight with nine passengers and two crew on board, the First Officer was the PF; estimating LAG 10:40 h and endurance of one hour plus thirty-five minutes maintaining an altitude of 3,000 ft above mean sea level (AMSL).
Fifteen minutes into the flight, there were repeated illuminations of ‘TRIM FAIL’ and Digital Automatic Flight Control System (DAFCS) indications. The Emergency Operating Procedure (EOP) was consulted and it recommended that the helicopter be flown hands and feet on the control.
At 10:08 h, about 75 NM from LAG, initial contact was made with Lagos Approach. The Pilot Flying (PF) complained of the collective being heavy and the autopilot decoupling. There was loss of power, high rate of descent and decreasing altitude. The Captain observed a slight turn to the right and asked the PF to check heading and the PF reported that there was problem with the compass.
The instrument readings were inaccurate and inconsistent, and the aircraft started drifting to the right.
At about 66 NM on radial 145o from LAG, the Captain made a distress call “MAY DAY, MAY DAY, MAY DAY” on the Approach frequency. Afterwards, the aircraft stabilized at an altitude of 1,500 ft AMSL on a NE-E heading and the Captain briefed the passengers that they would have to ditch the aircraft.
At about 10:19 h, 5N-BQJ made a controlled landing on water at approximately 77 NM on radial 139o of ‘LAG VOR’. Coordinates of the position was 05o45’43” N, 004o13’54” E.
The investigation identified the following causal and contributory factors:
The crew switched the Compass to “FREE” DG mode for Landing on the helideck at Erha FPSO, and did not return to the “SLAVE” mode after take-off which caused the trim fail to cut off consistently which in turn disengaged the autopilot as a result of the unsynchronised heading inputs.
Four Safety Recommendations were made.
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