Created Thursday, Jan 9th 2025 20:20Z, last updated Thursday, Jan 9th 2025 20:20Z
A One Air Boeing 747-400 freighter, registration G-UNET performing flight HC-311 from Muscat (Oman) to London Heathrow,EN (UK) with 4 crew, landed on Heathrow's runway 27L and taxied to the apron. A subsequent post flight inspection revealed a panel was missing from the underside of the wing. The operator filed a mandatory occurrence report to the CAA, however, the report was not forwarded to the AAIB.
Two months later, on Mar 7th 2024, the panel was found in the grass left of the touch down area of the runway and the AAIB was informed.
The AAIB released their final bulletin concluding the probable causes of the serious incident were:
The left wing panel detached from the aircraft after touchdown, most likely due to fatigue cracking of its supporting rib. This rib was known to suffer from cracks and the aircraft manufacturer had published a Service Letter with actions to help mitigate it, although the actions did not always prevent it. Analysis by the aircraft manufacturer indicated that there was low probability of a detached wing panel causing damage that would result in either an injury or prevent continued safe flight. The main hazard was considered to be runway FOD which could cause damage to a landing or departing aircraft. FOD radar detection systems are an effective mitigation, but not all major airports are equipped with them.
The AAIB analysed:
The left wing panel was found 600 m beyond the threshold for Runway 27L indicating that it probably detached from the aircraft after touchdown when the spoilers were deployed.
The panel most likely cracked and then failed at its supporting rib first, before failing at the leading edge honeycomb structure. The aircraft manufacturer’s Service Letter 747-SL57-101-B indicated that this rib was known to suffer from fatigue cracks and failures, and recommended mitigating action involving adjusting spoiler support rib clearances. There was no documentary evidence that the actions in the SL had been carried out on the incident aircraft; however, when the opposite right wing was checked the clearances were within the limits of the SL.
The aircraft manufacturer’s analysis indicated that the loss of such a wing panel in-flight had an acceptably low probability of causing damage that would result in either an injury or continued safe flight.
The most likely hazard from a separated wing panel was considered to be runway FOD, which could cause damage to a landing or departing aircraft. It was runway FOD that caused the catastrophic accident to Concorde (F-BTSC) during takeoff from Charles de Gaulle Airport in July 20002. Heathrow Airport had a FOD radar detection system that would have detected the wing panel had it ended up on the runway surface. However, not all major airports worldwide are equipped with FOD radar detection systems. Mitigation therefore relies on runway inspections and aircraft design standards which address protection from damage caused by runway FOD.
