What happened
On 12 January 2009, a BD700 Global Express, registration N618WF, was performing a non-revenue commercial flight approaching Runway 26 at Luton Airport. The aircraft was on final approach with the autopilot engaged, following instructions to maintain a speed of 160 kt. As the aircraft reached four nautical miles from the threshold, the crew selected full flaps and reduced speed to 121 kt.
While descending through approximately 210 ft above the touchdown zone, the aircraft encountered a disturbance, likely a wind gust. This caused the aircraft to roll to the left, then to the right, and back to a left bank. During this period, the nose pitch increased significantly. The autopilot disengaged between 10 ft and 2 ft radar altitude, leaving the aircraft in a nose-up, left-wing-low attitude. Consequently, the left wingtip struck the runway surface just before the left landing gear made contact. The crew was unaware of the impact until a ground marshaller pointed out the damage after parking.
The investigation
Investigators examined the aircraft's flight data recorder (FDR) and the manufacturer's data. The FDR confirmed that during the final 80 seconds of flight, the airspeed remained relatively stable, though it dropped from 124 to 114 kt in the five seconds preceding touchdown. The pitch attitude, which had averaged 4° nose up, increased to 8° nose up in the final three seconds.
Analysis of the radar altitude indicated an unusually high rate of descent. The investigation also considered the local terrain and airport procedures, noting that the UK AIP entry for Luton Airport specifies that the sloping terrain in the ILS approach area can result in a radio altimeter height reduction rate approximately double the normal rate.
Findings
- The primary cause of the wingtip strike was a wind disturbance occurring at 210 ft above the touchdown zone.
- The aircraft's left wing sustained damage to the trailing edge flap, flap track fairings, and the leading edge slat.
- The unusually high rate of radar altitude decrease, characteristic of the approach terrain at Luton, may have delayed the pilot's decision to disconnect the autopilot.
- The autopilot disengaged at an altitude below the manufacturer's recommended minimum of 50 ft AGL for precision approaches.