Description

On 14 June 2010, a Boeing 777-200 being operated by British Airways on a scheduled passenger se]]rvice from Singapore to London Heathrow with a relief crew present on the flight received indications of abnormal functioning of the right engine during a night take off in Visual Meteorological Conditions (VMC). Subsequent and directly related developments en route, including greater than planned fuel consumption which put the intended destination out of reach, led to the declaration of a PAN to ATC and diversion to Amsterdam. Inspection after flight found that parts of the right engine were damaged or missing and the latter were matched to previously unidentified debris recovered from the runway at Singapore. None of the 214 occupants were injured.

Investigation

An Investigation was carried out by the UK AAIB. It was noted that the aircraft commander had been PF for the departure and that one of the two augmenting crew members had been present in the flight deck for take off. At approximately 500 feet aal after take off, there was a fluctuation in the N1 indication for the right engine and related EICAS cautionary and advisory annunciations. No immediate action was prescribed and when thrust was reduced to climb setting at acceleration altitude, parameter indications for both engines settled in their normal range. Subsequent system interrogation and thrust lever movement checks did not indicate anything of undue concern and it was decided that the flight should be continued.

Possible causes were reviewed by the crew members present and included a bird strike, fan damage, false indications or a failure within the EEC or related systems. Once the aircraft had reached its initial cruising altitude the only evident discrepancy in engine indications was that the N2, N3, fuel flow and EGT for the right engine were slightly lower and the N1 slightly higher than the corresponding readings for the left engine. Engine vibration indications for that engine remained low.

Approximately 4 hours into the flight, an EICAS annunciation indicating that the right engine EEC had changed from ‘Normal’ mode to ‘Alternate’ mode had occurred and in accordance with the applicable Quick Reference Handbook (QRH) drill, the left engine EEC had also been switched to ‘Alternate’ mode. An hour later, over Afghanistan, it became clear that total fuel flow was higher than would be expected to the extent that reaching the intended destination with at least minimum fuel of 5,400 kg was becoming unlikely with the trend worsening. However with no suitable precautionary diversions available, it was decided to continue en route noting that this would eventually bring more suitable diversion options into range and the relief crew took over.

Just over three hours after this, a sudden “thud” had been heard accompanied by a slight movement of the aircraft. The relief crew observed that the required thrust setting and fuel flow had reduced and that the fuel remaining, although now showing insufficient to reach destination, had stopped deteriorating. As it was now daylight, and suspecting that a panel might have become loose and subsequently detached, an inspection of the right engine was made from the cabin but nothing abnormal was seen.

After consultation with the Company, it was decided to divert to Amsterdam where excellent weather prevailed and where multiple runways were available. Although it appeared probable that landing would occur with more than minimum reserve fuel, it was decided that in view of uncertainties, it would be prudent to declare a PAN on initial contact with diversion ATC, although the remainder of the flight was uneventful.

Initial assessments at Amsterdam of the damage to the aircraft found that “the left inner wall ‘D-duct’ on the right engine thrust reverser had separated from its engine and that a large portion of the turbine exhaust nozzle was missing. There was also damage to the inboard flap fairing and flaperon, consistent with the separation of the items from the engine, with scraping and gouge damage on the right lower wing skin and the right horizontal stabiliser. The manufacturer’s initial examination of the engine indicated that buckling damage to the inner wall D-duct was consistent with a ‘typical of loss of stability due to disbond of inner facesheet’ and that this form of failure had been seen on a number of previous occasions.”

It was noted that the investigated event was the first of its type to affect a British Airways aircraft but that there had previously been ten other events on Boeing 777 aircraft fitted with the same Rolls Royce RB211 Trent 895 engines and two others since. As a result of the earlier events, two successive Service Bulletins (SBs) had been issued by Boeing in 2005 and 2008 requiring specified engine inspections, at first one-off and then repetitively. A final SB to address the problem with a design modification was found to have been issued by Boeing in late 2009 but it was noted that “there was some initial delay in the approval by the European Aviation Safety Agency (EASA) of the design change included within this SB, as EASA was requesting further data and design substantiation from the airframe manufacturer” so that the approval had not been granted at the time of the investigated event.

The Final Report AAIB Bulletin: 10/2011 EW/C2010/06/05 of the Investigation was published on 6 October 2011. No Safety Recommendations were made.

Further Reading

• Airworthiness - The System
• Certification of Aircraft, Design and Production
• Damage Tolerance
• Uncontained Engine Failure