On 4 September 2009, a Boeing 744-400 being operated by Air India on a delayed scheduled passenger flight from Mumbai to Riyadh was awaiting take off in normal daylight when ATC advised that there was a fuel leak from the left side, that a fire had started and that the engines should be shut down. An emergency cabin evacuation was carried out using exits on the right hand side and there were 21 minor injuries to the 213 passengers with all 16 crew escaping without injury. The fire on the left hand side was quickly extinguished by the RFFS and aircraft damage was confined to that area.
An Investigation was carried out by the Indian DGCA. It was established that the flight had originally been scheduled to depart approximately 9 hours earlier but the allocated aircraft had returned to the gate twice due to a `technical fault’. The aircraft involved in the fire event was then substituted, but on the push back, the tow bar had failed causing a further delay. During the taxi out, several persons saw the fuel leak but were unable to contact the aircraft directly and when ATC tried, they used the aircraft registration which the crew did not recognise and then the call sign to which there was also initially no response. By the time the crew had recognised that ATC were calling them and responded to the advice of both fuel leak and a fire by commencing fire and engine shut down drills and calling the senior cabin crew to the flight deck, the cabin crew and some passengers had already seen the fire and an evacuation was ordered and carried out from the right hand side cabin exits. The flight crew evacuated from the upper deck prior to completion of the cabin evacuation where the senior cabin crew was the last to exit.
It was noted that Pratt & Whitney PW4056 engines were fitted to the aircraft. It was also noted that fire had been observed to start in No 1 (left outboard) engine about 45 seconds after it had been shut down. The RFFS had quickly arrived on the scene and the fire had already been out prior to completion of the passenger evacuation.
It was found upon examination of the aircraft that the fuel leak from the No 1 engine strut had led to a fire affecting that engine and its pylon which had then spread towards the adjacent inboard engine causing damage to the base of the LH wing. The cause of the fuel leak was found to be a loose fuel coupling which, although safety wired, was found loose with the safety wire having pulled through the coupling safety wire hole. It was established that there had been no recent maintenance activity in the area of the failed assembly.
It was not possible to determine what caused the loss of function of the safety wire by laboratory analysis of the failed parts. Boeing advised being aware of similar fuel coupling damage to other aircraft where it had been found that the coupling had not been tightened to the proper specification so that the coupling had rotated in both directions in service and the coupling material had eventually fractured. On the basis that this scenario was the most likely cause, Boeing highlighted the importance of correctly tightening all fuel couplings to the specified torque but advised that there had been no widespread world-fleet history of similar failures.
The Investigation noted that the failed coupling is only routinely accessed and inspected at ‘D’ Check and that the previous such check was over four years prior to the investigated event. However, the leaking coupling had been disturbed during work to replace a component in the same area at the more recent ‘C’ Check, a year prior to the investigated event.
The Investigation concluded that the Cause of the event was:
“complete dislodging of No. 1 strut fuel feed line coupling due to dislodging of tie wire from the failed tie wire hole is the cause for heavy fuel leak and leaked fuel falling on hot #1 engine resulted into fire.”
It was also concluded that Contributory Factors were as follows:
- Not tightening the coupling to the proper specification and procedure during maintenance resulting in ductile failure of (the) coupling material is the main contributory causative factor.
- Installation, maintenance or environmental variables.
- Failure of departure AME in adhering to the standard procedures and his perfunctory function.
- Lapses/failure of the pilots during walk around inspection.
- Non-conformance by the pilots- company operating procedures.
- Failure of ATC-SMC personnel for prompt and effective handling emergency situation.
- Lack of situational awareness and crew coordination.
Seven Safety Recommendations were issued as a result of the Investigation as follows:
- Appropriate corrective action as deemed fit should be taken on the involved captain, first officer, all Cabin crew and the Departure AME for their deficient performance and lapses.
- Appropriate corrective action as deemed fit should be taken on the SMC controller for his tardy and ineffective handling of the emergency situation.
- Air India shall Review maintenance program, its schedules and maintenance practices for more stringent, effective and frequent inspection and identification of fuel leak from the aircraft.
- The incident may be brought to the knowledge of all concerned.
- AAI (the ANSP) shall introduce, monitor proper training procedure to all ATC personnel for handling emergency situation.
- AAI (the ANSP) shall review the Existing System of documenting Departure/arrival register and flight progress strip for inclusion of information of aircraft registration.
- Installation of SMR at Mumbai airport shall be done immediately by concerned airport agencies.
The Final Report of the Investigation was issued on 16 July 2010.