What happened
On 5 March 2011, an Emirates Boeing 777-200ER, registration A6-EMH, departed from Moscow Domodedovo Airport for Dubai. Shortly after takeoff, while the aircraft was approximately 400 feet above the ground, the flight crew observed an Engine Indication and Crew Alerting System (EICAS) message indicating thrust asymmetry. During the climb, cabin crew members reported hearing a loud bang and seeing sparks emanating from the right side of the aircraft.
Following the initial alert, additional EICAS messages appeared regarding the right engine's Electronic Engine Control (EEC) mode, the turbine overheat sensor, and the engine fire loop. The crew followed established procedures to switch the EEC to alternate mode. While engine parameters eventually stabilized during the flight, pieces of the thrust reverser had separated from the aircraft. Although an initial runway inspection at Moscow found no debris, subsequent checks by airport authorities confirmed that parts of the thrust reverser were left on the runway. Upon landing in Dubai, the crew noted further small pieces separating from the aircraft, and a post-flight inspection revealed the missing component.
The investigation
The UAE GCAA AAIS investigation focused on the failure of the left-hand inner wall of the No. 2 engine's thrust reverser. This composite component, constructed with a carbon fiber core, is designed to be protected from engine heat by a thermal fire blanket.
Forensic examination of the failed part by Boeing, under NTSB supervision, determined that a previous repair had failed. The investigation established that the adhesive between the repair patch and the core had separated. Furthermore, the investigation looked into whether the thrust reverser had been mis-rigged, which could have introduced excessive loads to the weakened structure.
Findings
- The primary cause of the failure was residual thermal damage to the composite inner wall that remained unaddressed during a previous inspection and repair.
- The previous repair was ineffective due to inadequate cleaning of the core surface prior to the application of adhesive.
- The repair area was not expanded sufficiently to encompass the extent of the thermal damage.
- There was a possibility that improper rigging of the thrust reverser caused higher-than-normal mechanical loads on the panel.