26th of August 2008, Blog #518
A Boeing 747-400 had left Paris Charles de Gaulle and had crossed the Atlantic Ocean with 491 passengers and 18 crew on this day in 2008.
The destination of the flight was Montréal/Pierre Elliott Trudeau International Airport.
The aircraft in its final position. (© TSB Canada)
ATC cleared the aircraft for a straight-in approach for runway 24R in good weather (VMC conditions);
Clouds - Scattered at 24.000 feet
Visibility - 30 Statute miles
Wind - 290º at 5 knots
A stabilised approach was flown and the aircraft crossed the threshold, properly configured with the spoilers armed, auto brake selected (at position 3), and at the correct speed. Touchdown occurred in the touchdown zone of the runway, the ground spoilers deployed automatically, reverse thrust was selected and the auto brakes activated. Small rudder inputs kept aircraft tracking the centreline of the runway. At a speed of 80 knots, reverse thrust was selected to idle reverse.
When the speed reached ~65 knots the captain placed his hand on the nose wheel tiller, causing a small forward movement of the tiller, causing a small deflection of the nose wheels to the right. This caused the aircraft to veer to the right slightly, which was corrected by a small left rudder input.
The nose wheel steering tiller ( © TSB Canada)
At a speed of ~45 knots, the reversers were stowed and the autobrake disengaged. At that time the aircraft veered to the right again. The crew attempted to correct this by applying full left rudder and forward nosewheel tiller inputs. This was unsuccessful and the rate of turn to the right rapidly increased. Maximum brake pressure was applied in an attempt to stop the aircraft on the runway. This was not sufficient to stop the aircraft on the paved surface of the runway. The nose wheel left the paved surface on the right-hand runway edge. When the aircraft came to a stop it was on a heading of 277º magnetic, with the nosewheels 26 feet from the runway surface.
Landing rollout events (© TSB Canada)
ATC was informed, the APU was started and the engines were shut down. Passengers were disembarked after some time, there were no injuries. Subsequent aircraft aborted their approach and were rerouted to a different runway.
The Transportation Safety Board of Canada (TSB) was alerted and an investigation was launched. In their report, they provide an in-depth look at the occurrence, technical details, and the investigation. The investigation report, on which this blog is based, is available for the readers' reference by clicking on the .pdf file at the end of this blog.
Nose wheel skid marks commenced in a straight line on the runway centreline and remain on the centreline markings and centreline lighting over a distance of approximately 600 feet. The skid marks then move towards the right edge of the runway, resulting in a total skid distance of approximately 1160 feet.
Nose wheel skid marks (© TSB Canada)
The main landing gear tire skid marks commence approximately 800 feet after the nose wheels began to skid, and continued for approximately 210 feet. The right main landing gear tires stopped 9 feet from the edge of the runway.
Main gear tire marks, heavy braking ( © TSB Canada)
The TSB identified the following findings as to the cause;
The placement of the hand on the tiller at high speed resulted in an unintentional tiller deflection, causing the nose wheels to skid when the rudder was used to counter the turn.
With his left hand already placed on the tiller, the pilot flying (PF) inadvertently pushed the deflected tiller further forward and down, resulting in an increased right turn, causing the aircraft to veer to the right and depart the runway surface.