T - was a Dark and stormy night, The Clouds were thicker than usual, and were busy dumping a record Monsoon down poor.
The time was oh about 10:45 at night I supose when QANTAS flight 001 was slotting her way to the Runway somewhere below.................................... Her crew , the finest and most trained in the world. Had no idear what would be the main talk at crew Drinks that night.
Bangkok is a hot and steamy place, pron to torrentual down poors of rain, that only last a few hours at most. but are so heavy the water cant run off in a hurry and lightly floods roads and streets at times.
The overrun occurred after the aircraft landed
long and aquaplaned on a runway which was affected by water following very heavy rain.
The aircraft sustained substantial damage during the overrun. None of the three flight crew,
16 cabin crew or 391 passengers reported any serious injuries.
In terms of overall accident statistics, runway overruns are a relatively common event. Of the
49 accidents involving western-built high-capacity jet aircraft reported during 1999,
11 were landing overruns. Landing overruns typically occur when the runway is wet or
contaminated and/or the aircraft is high and fast during final approach.
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).
The Qantas One crew noted no effect from the weather until visibility reduced when the
aircraft entered very heavy rain as it descended through 200 ft on late final approach. The
aircraft then started to deviate above the 3.15 degree glideslope, passing over the runway
threshold at 169 kts at a height of 76 ft. Those parameters were within company limits. (The
target speed for the final approach was 154 kts, and the ideal threshold crossing height was
44 ft.)
When the aircraft was approximately 10 ft 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 kts, 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.
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