What happened
On 19 July 1998, a Lockheed L1011-385-1-14, registration G-BBAF, was operating a scheduled charter flight from London Gatwick to Kos Airport, Greece. The flight, carrying 357 passengers and 13 crew members, was performing a night approach to Runway 33. During the final stages of the descent, the aircraft experienced a sudden loss of altitude and a significant sink rate. In an effort to arrest this descent, the pilot increased the pitch attitude, which resulted in the rear of the aircraft contacting the runway surface.
The impact caused extensive structural damage to the lower fuselage near the rear pressure bulkhead and abrasions to the tail skid. Despite the severity of the impact, there were no injuries to the passengers or crew. The crew was initially unaware of the extent of the damage until a heavy landing inspection was performed after the aircraft had been parked.
The investigation
The investigation examined the aircraft's technical state, the crew's duty cycles, and the environmental conditions at Kos Airport. Investigators analyzed flight data from the FDR and QAR, noting that the autothrottle system had maintained an airspeed significantly higher than the target speed. The investigation also looked into a known technical defect regarding the stall warning system, which had been triggering intermittently during previous sectors.
Furthermore, the investigation reviewed the airfield's visual aids and the accuracy of the approach charts. It was noted that the crew was operating during a period of reduced alertness due to being called from standby duty and having been awake for over 20 hours. The investigation also scrutinized the impact of wind changes and the terrain near the runway threshold.
Findings
- The primary cause of the accident was the sudden loss of updraft and headwind just prior to touchdown, which caused the aircraft to sink below the intended glidepath.
- The pilot's attempt to correct the sink rate by increasing pitch caused the aft fuselage to strike the runway.
- A technical fault in the Flight Control Electronic System caused the stall warning (stick shaker) to activate prematurely, which also deactivated the Direct Lift Control (DLC) system, contributing to a destabilized approach.
- The crew was likely experiencing reduced alertness due to fatigue, having been awake for more than 20 hours.
- An error in the airfield charts regarding the runway slope contributed to a visual illusion that the aircraft was higher than it actually was.
- The aircraft was flying with an autothrottle setting that maintained speeds 15 to 20 knots above the target Vref speed.