What happened
On 19 February 2005, a Boeing 777-21H, registration A6-EMF, was preparing for a scheduled passenger flight from Birmingham Airport to Dubai. During the takeoff roll, the outer skin of panel 427AL, located on the inboard side of the right engine pylon, separated from the structure and fell onto the runway. Following the departure, a subsequent aircraft noticed large debris on the runway, which was later confirmed to be a metallic component from the departing aircraft.
While climbing through FL260, the crew noticed a vibration that intensified as the aircraft gained altitude. The climb was terminated at FL280, and the crew diverted to London Gatwick. To ensure the aircraft remained within maximum landing weight limits, 20 tons of fuel were jettisoned. The landing at Gatwick was completed without further incident. Upon inspection, it was confirmed that the outer skin of the right engine pylon panel was missing.
The investigation
The AAIB investigation focused on the structural failure of the pylon panel. Although the damaged panel was returned to the operator for repair before it could be examined by the AAIB, photographs revealed evidence of heat damage on the forward edge of the remaining structure. The manufacturer, Boeing, suggested that the most probable source of this heat was a leak of core air from the engine.
Records indicated that this specific aircraft, A6-EMF, had a history of similar issues. In 2003, a different panel (418AR) on the left engine pylon had also delaminated, showing similar heat damage. Furthermore, a third incident involving the delamination of panel 418AR occurred on 3 June 2005 in Islamabad, Pakistan.
Findings
- The primary cause of the panel separation was delamination of the aluminium honeycomb core skin.
- The forward edge of the panel showed evidence of heat damage, likely caused by an engine core air leak.
- While the temperatures reached were within the design service limits for the adhesive, the heat likely weakened the bond strength.
- The combination of reduced adhesive strength, aerodynamic loads, sonic vibrations, and cyclic thermal stresses contributed to the failure.
- No other Boeing 777 aircraft in the manufacturer's fleet were reported to have similar issues.