Runway excursion Accident Boeing 747-438 VH-OJH, Thursday 23 September 1999
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Date:Thursday 23 September 1999
Type:Silhouette image of generic B744 model; specific model in this crash may look slightly different    
Boeing 747-438
Registration: VH-OJH
MSN: 24806/807
Year of manufacture:1990
Total airframe hrs:41151 hours
Cycles:6002 flights
Engine model:Rolls-Royce RB211-524G
Fatalities:Fatalities: 0 / Occupants: 410
Other fatalities:0
Aircraft damage: Substantial, repaired
Location:Bangkok International Airport (BKK) -   Thailand
Phase: Landing
Nature:Passenger - Scheduled
Departure airport:Sydney-Kingsford Smith International Airport, NSW (SYD/YSSY)
Destination airport:Bangkok-Don Muang International Airport (BKK/VTBD)
Confidence Rating: Accident investigation report completed and information captured
The first officer was the handling pilot for the flight. The crew elected to use flaps 25 and idle reverse as the configuration for the approach and landing, in accordance with normal company practice (since December 1996).
At various stages during the approach to runway 21L, the crew were informed by air traffic control that there was a thunderstorm and heavy rain at the airport, and that visibility was 4 km (or greater). At 2240, a special weather observation taken at Bangkok airport noted visibility as 1,500 m and the RVR for runway 21R as 750 m. The Qantas 1 crew was not made aware of this information, or the fact that another aircraft (callsign Qantas 15) had gone around from final approach at 2243:26. At 2244:53, the tower controller advised that the runway was wet and that a preceding aircraft (which landed at approximately 2240) reported that braking action was ‘good’.
The Qantas 1 crew noted no effect from the weather until visibility reduced when the aircraft entered very heavy rain as it descended through 200 feet on late final approach. The aircraft then started to deviate above the 3.15 degree glideslope, passing over the runway threshold at 169 knots at a height of 76 feet. Those parameters were within company limits. (The target speed for the final approach was 154 knots, and the ideal threshold crossing height was 44 ft.)
When the aircraft was approximately 10 feet above the runway, the captain instructed the first officer to go around. As the first officer advanced the engine thrust levers, the aircraft’s mainwheels touched down (1,002 m along the 3,150 m runway, 636 m beyond the ideal touchdown point). The captain immediately cancelled the go-around by retarding the thrust levers, without announcing his actions. Those events resulted in confusion amongst the other pilots, and contributed to the crew not selecting (or noticing the absence of) reverse thrust during the landing roll. Due to a variety of factors associated with the cancellation of the go-around, the aircraft’s speed did not decrease below the touchdown speed (154 kts) until the aircraft was 1,625 m or halfway down the runway.
The investigation established that, during the landing roll, the aircraft tyres aquaplaned on the water-affected runway. This limited the effectiveness of the wheelbrakes to about one third of that for a dry runway. In such conditions and without reverse thrust, there was no prospect of the crew stopping the aircraft in the runway distance remaining after touchdown. The aircraft overran the 100 m stopway (at the end of the runway) at a speed of 88 knots, before stopping 220 m later with the nose resting on an airport perimeter road.
The depth of water on the runway when the aircraft landed could not be determined but it was sufficient to allow dynamic aquaplaning to occur (i.e. at least 3 mm). The water buildup was the result of heavy rain on the runway in the preceding minutes, and possibly because the runway was ungrooved.
During the examination of the performance of the aircraft on the runway, it became evident that the flaps 25/idle reverse thrust landing procedure used by the crew (and which was the ‘preferred’ company procedure) was not appropriate for operations on to water-affected runways. The appropriate approach/landing procedure was flaps 30/full reverse thrust. This had the characteristics of a lower approach speed, of being easier to fly in terms of speed control and runway aim point (for most company pilots), and of providing maximum aerodynamic drag after touchdown when the effectiveness of the wheelbrakes could be reduced because of aquaplaning. Had this configuration been used, the overrun would most probably have been avoided.
As with other company B747-400 pilots, the crew had not been provided with appropriate procedures and training to properly evaluate the potential effect the Bangkok Airport weather conditions might have had on the stopping performance of the aircraft. In particular, they were not sufficiently aware of the potential for aquaplaning and of the importance of reverse thrust as a stopping force on water-affected runways.




photo (c) Ian Jenkins; London-Heathrow Airport (LHR/EGLL); 25 August 2008

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