On 23 July 2000, a Boeing 747-200 being operated by Royal Air Maroc on a scheduled passenger flight from New York to Montreal overran the temporarily restricted available landing runway length after the aircraft failed to decelerate sufficiently during a daylight landing with normal on-ground visibility. It struck barriers at the displaced runway end before stopping 215 metres further on. Shortly before it stopped, ATC observed flames coming out of the No. 2 engine and advised the flight crew and alerted the RFFS. However, no sustained fire developed and the aircraft was undamaged except for internal damage to the No 2 engine. No emergency evacuation was deemed necessary by the aircraft commander and there were no occupant or other injuries.
An Investigation was carried out by the Canadian Transportation Safety Board (TSB). It was established that the crew were all familiar with operations at the airport, were aware of the reduced LDA of 2460 metres compared to the normal 3385 metres, had noted the presence of storm cell near the airport and had considered the consequent possibility of wind shear. The First Officer had been the PF and had made a firm touchdown at slightly higher speed than ideal about 520 metres from the runway threshold. Shortly before touchdown, the previously light and variable surface wind was found to have become stronger and more directionally-specific to give a tailwind component of up to 15 kts. The auto brake had been set to minimum contrary to the recommended ‘medium’ setting for wet or slippery conditions, when firm braking is needed and for any landing where the landing roll distance is limited.
The Investigation calculated that on a wet runway with a 15-knot tailwind component and flying at Vref + 5 knots, the landing distance required for the prevailing aircraft weight from a screen height of 50 feet above the runway threshold was about 2400 metres with medium auto brake and 2830 metres with minimum as used. However, this takes no account of thrust reverser use which, for normal operations on short, wet or slippery runways, involves maintaining the reversers at maximum power until the aircraft reaches 60 kts and then reducing reverse thrust to 60% N1 at 40 knots. In an emergency, the reversers can be maintained at maximum until the aircraft comes to a complete stop but it is noted that this can result in engine overheating. In this case, the No. 2 engine did overheat and shut down automatically after the aircraft passed the designated runway end.
The Investigation noted that runway friction coefficients are not available for wet runways, so pilots have no alternative but to rely on the assessment, when available, of braking effectiveness reported by other pilots who have already landed to determine whether braking effectiveness will be sufficient for their aircraft type. It was noted that the effect of this was that a pilot decision to accept a given runway for landing is frequently based on inaccurate and often incomplete information.
Since it was established that only 1.6 mm of rain had fallen in the 30 minutes before the accident landing and the construction characteristics of the runway provided for sufficient drainage, it was reasonable to believe that the runway was wet but not contaminated. However, the combination of a wet runway and rubber accumulation at the TDZ together created conditions conducive to viscous hydroplaning and it was concluded that all the available evidence pointed to delayed wheel spin up and delayed auto brake initiation.
It was noted that with the tailwind component a few seconds before touchdown and the wet runway, even if medium auto brake had been set, and the approach speed had been maintained at Vref + 5 knots, there was very little margin for error.
The Findings of the Investigation, taken verbatim from the Report, were as follows:
Causes and Contributing Factors
- The landing technique used by the pilot flying reduced much of the excess speed during the flare and contributed to the increase in landing distance.
- The wet runway and the rubber accumulation on the runway created conditions conducive to viscous hydroplaning, thereby contributing to the increase in stopping distance.
- The automatic braking system was set to minimum, which contributed to the increase in stopping distance. The recommended setting was medium.
- The runway friction coefficient indicated that the runway was slippery when wet, but this information was not provided to the pilots. This information might have prompted the flight crew to request a longer runway or use medium automatic braking rather than minimum.
- The flight crew did not use the tables for calculating landing distance; consequently, they did not feel it was necessary to request a longer runway for the landing.
- Aéroports de Montréal (ADM) did not follow Transport Canada's recommendations to issue a notice to airmen (Notice To Airmen) indicating that the runway could be slippery when wet. The flight crew was thus deprived of key information.
- While crossing the runway threshold and during much of the landing roll, the aircraft was subjected to an average tailwind component of about 15 knots, thereby increasing the stopping distance.
- Transport Canada and ADM have different interpretations of paragraph 18.104.22.168 of Aerodrome Standards and Recommended Practices (TP312) as to the action required at certain runway friction levels.
It was noted that removal of rubber deposits from the accident runway surface was effected on 23 August 2000 by a contractor hired by ADM and that this restored the reference friction coefficient to above the required standard.
This report concludes the Transportation Safety Board's investigation into this occurrence. Consequently, the Board authorized the release of this report on 30 August 2001.
The release of the Final Report of the Investigation was authorised on 30 August 2001 and it may seen in full at SKYbrary bookshelf: Aviation Investigation Report A00Q0094
No Safety Recommendations were made.