Cause of Bristow helicopter crash yet unknown, probe ongoing, says AIB
ACCIDENT Investigation Bureau (AIB) has revealed in its preliminary report on the air crash involving SIKORSKY S-76C+ Helicopter belonging to Bristow Helicopters Limited, Nigeria, with registration 5N-BGD, which occurred at Oworonshoki area of Lagos on the 12th of August, that the cause of the accident has not been fully ascertained, as investigation is still going on.
However, it noted that during the preliminary investigation, AIB discovered that the Forward Main Servo Input Control Pushrod Assembly had failed, adding that the control pushrod tube separated from control rod end with the bearing and the Jamnut, which may have led to a malfunctioning of the engines of the aircraft.
According to AIB, the crew did not declare an emergency as the Flight Data Recorder (FDR) indicated that the distress lasted for about 12 seconds.
The report revealed that field examination suggested that number two engine suffered an uncontained failure and the preliminary flight recorder data indicated that at 1000ft and 120Kts, the helicopter experienced sudden pitch up, and left roll with varying attitude of yaw, roll and pitch for 12 seconds until it impacted water at about 1531hrs.
After examination of the number two engines, which revealed damage associated with uncontained failure of internal components, the engines have been sent to the manufacturer in France, it noted.
It also, stated that the crew were certified and qualified to conduct the flight in accordance with applicable Nigerian Civil Aviation Regulations, adding that the captain and co-pilot had 1,077.45 and 570 hours flight time on the aircraft type, respectively.
Addressing Journalists on the update of its investigation report on Monday, in Lagos, the Commissioner and Chief Executive Officer,Dr. Felix Abali stated that the cause of the accident has not been fully determined, as the investigation is still ongoing.
He added that the interim safety actions have been taken by Federal Aviation Administration (FAA) and Sikorsky by the issuing of Emergency Airworthiness Directives (EAD) and Alert Service Bulletin (ASB) respectively on the Main and Tail Rotor Servo Input Rod assembly.
Abali noted that this was to ensure the continued airworthiness and security of the assemblies, disclosing that Bristow Helicopters Nigeria Limited had earlier issued two Technical Directives as a safety action.
According to the Commissioner, the National Transportation Safety Board (NTSB) Laboratory preliminary metallurgical examination of the Forward Main Rotor Servo Input Control Pushrod revealed that the separation was in a pre-impact condition
Abali, who said that a separate Cockpit Voice Recorder was also installed on the helicopter, stated that the recorders were recovered by professional divers in good condition from the Lagoon on the second day of the accident but the combined recorder had few punctures.
His words: “The recorders were sent to Air Accident Investigation Branch United Kingdom for data download. During the download at the AIB it was discovered that the combined Solid State Voice/Flight Data recorder only contained information of the flight data while the separate Cockpit Voice Recorder contained audio data. However, they were both successfully downloaded and are now being analyzed”.
“The accident occurred when 5N-BGD was on the inbound flight of a round trip that originated from Lagos. On the outbound flight, 5N-BGD arrived SEDCO Express at about 1448hrs reportedly without incident with two passengers. This was also the first flight of the day and the helicopter did not re-fuel for the trip back to Lagos”.
However, AIB reported that the flight preceding the accident aircraft was without incident and there was good communication between the helicopter and the Control Tower before the accident.
With the Preliminary report, AIB has issued some Interim Safety recommendations of which one is for Sikorsky Aircraft Corporation to consider a redesign of the affected control pushrod assembly by introducing additional wire locking safety features between the Jamnut and the Pushrod to enhance better security.
The Jamnut was loose and was not seating against the control rod. The flight departed from the SEDCO Express Rig and was uneventful until about five minutes to landing.
AIB called on the Nigerian Civil Aviation Authority (NCAA) to immediately carryout appropriate oversight action on all the Sikorsky S-76 series helicopters flying in Nigeria to ensure the implementation of the Emergency Airworthiness Directives (EAD) and Alert Service Bulletin (ASB) issued by FAA and Sikorsky Aircraft Corporation.
Said Abali: “There was no evidence of fire outbreak before and after the crash. The life rafts on the helicopter were observed deflated and floating in the lagoon but were not deployed. The wreckage of the helicopter was confined in a small area around the crash site in the lagoon.
The AIB stated that the main wreckage was submerged in the lagoon, adding that the two raft inflation bottles under the crew seats were still fully charged.
The bureau noted that the helicopter was manufactured in 2003, with total airframe hours of 10,258:0913, and it was maintained in accordance with approved maintenance schedules.
“The flight preceding the accident aircraft was without incident. There was good communication between the helicopter and the tower before the accident,” he said.
It also recommended that the Nigerian Civil Aviation Authority should immediately carry out appropriate oversight action on all Sikorsky S-76 series helicopters flying in the country.
This, according to the AIB, is to ensure the implementation of the Emergency Airworthiness Directives and Alert Service Bulletin issued by the FAA and Sikorsky Aircraft Corporation.
AIB equally recommended that the manufac-turer of the ill-fated helicopter should consider a redesign of the affected control pushrod assembly by introducing additional wire locking safety features between the “Jamnut and the Pushrod to enhance better security.”