What happened
On 17 January 2008, a Boeing 777-236ER, registration G-YMMM, was involved in an accident during landing at London Heathrow Airport. The aircraft, operated by a commercial carrier, encountered unexpected ground conditions upon touchdown. The impact with the soft, non-homogeneous ground at the accident site led to significant structural distress, including the distortion of the wing rear spars and damage to the landing gear assembly.
The investigation
Investigators examined the aircraft's structural integrity and the physical characteristics of the impact site. The investigation included complex finite element modeling to simulate various landing scenarios, comparing impacts on hard runways versus the soft ground encountered during the accident. Researchers analyzed the behavior of the main landing gear (MLG) fuse pins and the drag brace assembly. The study specifically looked at how the presence of broken concrete and rubble within the soil at the accident site influenced the load transfer during the landing sequence. Simulations (specifically Run C) were used to replicate the accident parameters, including the aircraft's pitch, roll, and yaw at the moment of impact.
Findings
- The primary cause of the structural damage was the interaction between the landing gear and the soft, non-homogeneous ground.
- Unlike a hard runway impact, which would trigger a rapid, progressive failure of the MLG fuse pins, the soft ground delayed the buildup of shear forces.
- This delay prevented most fuse pins from reaching their programmed failure thresholds, allowing excessive loads to be transferred into the wing rear spars.
- The resulting forces caused significant distortion and buckling in the rear spar regions near the drag brace attachments.
- The presence of embedded rubble and broken concrete at the site made the soil behavior difficult to predict and contributed to the unusual load paths experienced by the airframe.