What happened
On 25 May 1998, a Concorde Type 1 Variant 102, registration G-BOAC, was conducting a scheduled public transport flight when it experienced a structural failure. While climbing through FL 415 at Mach 1.6, the flight crew felt a brief shudder lasting several seconds. Although initial engine checks showed no abnormalities, a crew member later inspected the aircraft's exterior through a cabin window and discovered that a portion of the No 3 left elevon had separated. The remaining upper skin of the control surface was observed to be oscillating rapidly.
Following the discovery, the crew requested clearance to decelerate and return to London Heathrow. After a period of communication delays with air traffic control, the commander initiated a 180-degree turn at Mach 1.96. During the descent and deceleration phase, the aircraft experienced a period of significant airframe buffet as it passed through the transonic regime. The aircraft eventually landed at Heathrow without further incident, though the emergency services were present on the airfield in anticipation of a more serious situation. There were no fatalities and no injuries among the 53 passengers and 11 crew members.
The investigation
The AAIB investigation focused on the structural integrity of the failed elevon, specifically examining the trailing edge which had undergone significant repairs in previous years. Investigators analyzed the metal honeycomb construction and the adhesive bonding used to secure the aluminum skins. The examination of the remaining structure revealed that while the core remained bonded to the upper skin, it had completely separated from the lower skin.
Technical analysis at DERA Farmborough confirmed that the fractures in the skin were the result of shear-type overload. However, because the specific pieces of the elevon that detached during the flight over the ocean were unrecoverable, the exact origin of the failure could not be pinpointed. The investigation also scrutinized the effectiveness of the existing non-destructive examination (NDE) protocols used by the operator to detect subsurface flaws.
Findings
- The primary cause of the failure was a progressive disbond of the elevon structure that reached a critical size, leading to instantaneous failure.
- The failure likely originated in the area of the previously repaired trailing edge.
- Existing NDE techniques were unable to inspect the integrity of the metal-metal bond lines or the skin-to-core bonds located underneath the overlapping repair patches.
- Approximately 50% of the repaired area was effectively uninspectable using the technology available at the time.
- The aircraft remained controllable despite the loss of a significant portion of the control surface, validating the manufacturer's design redundancy.