On 7 October 2014, the Air Canada Airbus A330 was operating as flight ACA875 from Frankfurt, Germany, to Montréal-Pierre Elliott Trudeau International Airport with 217 people aboard. There was a thunderstorm north of the airport as the aircraft was on approach to Runway 24R in daytime visual conditions. Runway 24R was the only runway in operation, and the flight crew had been advised that the runway lights were out of service. During the final approach, the aircraft entered a heavy rain shower and encountered a strong right crosswind. It then deviated from its path before touching down to the left of the runway centreline. Soon after, the outboard tires of the left main landing gear departed the runway surface for a distance of approximately 600 feet. The aircraft returned to the centreline before taxiing to the terminal gate, where the passengers disembarked without further event.
The investigation determined that during the approach in the presence of a thunderstorm, a pilot-induced aircraft rolling movement resulted in the aircraft being in a left bank as it crossed the runway threshold, which, combined with a strong right crosswind, caused it to drift rapidly to the left. After crossing the runway threshold, the intensity of the rain suddenly increased, causing the pilot flying to have very few visual references. The rain and the absence of runway lighting made it difficult to detect the aircraft's lateral movement and prevent the runway excursion. In addition, during the final approach, weather conditions had changed rapidly to those requiring runway lighting. As the runway lights were not working, that runway should not have been used under those weather conditions.
This occurrence demonstrates how flight conditions near thunderstorms can change dramatically and abruptly, posing a risk to flight safety. As part of its investigation (A05H0002) into the 2005 Air France runway overrun in Toronto, the TSB issued a recommendation (A07-01) calling on Transport Canada (TC) to establish clear standards for limiting approaches and landings in convective weather. TC issued an Advisory Circular to alert Canadian air operators to the hazards associated with flight operations in or near convective weather conditions and did propose that this issue be addressed at the international level. However, it stopped short of issuing the recommended standards. If TC does not take action to develop clear standards for avoiding thunderstorms during approach and landing, approaches in the presence of thunderstorms will continue, exposing aircraft to multiple, unpredictable hazards.
The report also notes that Montréal-Pierre Elliott Trudeau International Airport is not equipped with a low-level wind shear alert system, nor is it required to by regulation. If airports are not equipped with a low-level wind shear alert system, crews landing may not be aware of the presence of rapidly changing wind direction and speed, and therefore are exposed to the risk of approach-and-landing accidents.
Following the occurrence, Aéroports de Montréal, the operator of Montréal-Pierre Elliott Trudeau International Airport, reviewed conditions for closing a runway when approach and runway lighting is out of service. Air Canada also developed new guidance for its flight crews regarding approach and visibility requirements.
See the investigation page for more information.