What happened
On 24 October 1998, a Fokker 100, registration G-UKFN, was performing a scheduled public transport flight from Jersey to Southampton. During the final approach to Runway 20, the aircraft encountered turbulent conditions and a sudden, heavy downpour. The crew noted that the minimum speed indication disappeared from the primary flight display and observed a rapid decay in airspeed.
In response to the airspeed drop, the commander disconnected the autopilot and manually advanced the power levers to regain speed. Although the aircraft stabilized, the approach became destabilized, and the aircraft touched down approximately 300 metres beyond the ideal touchdown point.
Upon landing on the wet surface, the crew initially used the autobrake set to medium. As the aircraft approached the end of the runway, the commander applied manual braking, and the crew eventually selected emergency reverse thrust. Despite these efforts, the aircraft could not be stopped within the remaining paved area, exiting the runway and coming to rest between the runway end and the arrester bed. There were no injuries to the 96 passengers or 5 crew members on board.
The investigation
The AAIB examined the aircraft's flight recorders, which revealed that the airspeed had dropped to approximately 119 kt CAS. The investigation also involved simulations by the aircraft manufacturer to determine if the autothrottle had responded to an incorrect speed selection or if windshear was the primary driver of the airspeed loss.
Engineers analyzed the runway conditions, noting that while the surface was initially assessed as 'Wet', a heavy rain shower shortly before touchdown likely transitioned the state to somewhere between 'Wet' and 'Flooded'. The investigation also reviewed the braking performance, calculating that the aircraft required significantly more distance to stop than was available given the touchdown point and the runway's surface state.
Findings
- The approach became destabilized due to the crew's manual intervention to correct a rapid airspeed decay.
- A combination of windshear events, specifically a fluctuating headwind component, contributed to the loss of airspeed.
- The runway surface condition deteriorated rapidly from 'Wet' to a state approaching 'Flooded' due to a heavy rain shower just before arrival.
- The aircraft touched down too far down the runway and at a speed higher than ideal for the prevailing conditions.
- The commander did not apply maximum braking or maximum reverse thrust immediately upon touchdown, which would have been necessary to prevent the overrun.