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AIB releases Bristow crash prelim report, interim safety actions

Crew and passengers of the Sikorsky S-76C+ Helicopter,  5N-BDG belonging to Bristow Helicopters Nigeria Limited that claimed the lives of 6 of the 12 people on-board  did not register a Mayday call before the helicopter crashed at the Oworonshoki area of Lagos state.

retrieval of the crashed Bristow Helicopter
According to the Accident Investigation Bureau (AIB) Preliminary report released earlier today, the crew did not declare an emergency as the Flight Data Recorder (FDR) indicated that the distress lasted for about 12 seconds.
The AIB also informed that field examination suggested that No. 2 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 No.2 engine which revealed damage associated with uncontained failure of internal components, the engines have been sent to the manufacturer in France.
During the preliminary investigation, AIB discovered that the Forward Main Servo Input
Control Pushrod Assembly had failed. The Control Pushrod tube separated from Control rod end with the bearing and the Jamnut.
 The Jamnut was loose and was not seating against the Control Rod.
National Transportation Safety Board (NTSB) Laboratory preliminary metallurgical examination of the Forward Main Rotor Servo Input Control Pushrod revealed that the separation was a pre-impact condition.
Pictures also displayed by the AIB showed that the helicopter was destroyed by impact forces with water, the tail rotor area, cockpit area were all totalled as a result of the crash.
However, the AIB reports 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.
Although the cause of the accident has not been fully determined, as the investigation is still
Ongoing, helicopter manufacturers, Sikorsky and Federal Aviation Administration (FAA) in the course of the investigation have also issued Interim Safety Actions taken as a result of the outcome of AIB preliminary investigation:
On the 10th of September, 2015, Sikorsky Aircraft Corporation issued Alert Service
Bulletin (ASB) 76-67-57 on all S-76 model helicopters equipped with Control Pushrod
Assembly P/N 76400-0034-059 and 76400-00014-071.
The purpose of this is: “To perform a onetime inspection of installed Forward, Aft and Lateral Main
Servo Input Control Pushrod s and Jamnuts and Tail Servo Input Control Pushrods and
Jamnuts for proper installation, condition and security followed by application of
slippage mark on all Main and Tail Servo Input Control Pushrod Jamnuts”.
 “Compliance is essential. The instructions outlined herein shall be accomplished prior to next flight originating from a maintenance facility or not to exceed 5 flight hours from issue date of this ASB”.
 On the 14th September, 2015, The Federal Aviation Administration (FAA) issued
Emergency Airworthiness Directives (EAD) 2015-19-51 to owners and operators of
Sikorsky Aircraft Corporation model S-76A, S-76B, S-76C and S-76D helicopters. This
was related to service information from Sikorsky issued Alert Service Bulletin No. 76-67-
57 of 10th September, 2015.
With the Preliminary report, the 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.
AIB also 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.

 

Reports and recommendations provided by the AIB are used to forestall accidents and entrench safety and not a tools for fault finding

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