Canadian investigators examining the Air France Airbus A340-300 overrun at Toronto Pearson Airport two years ago are insisting that pilots are given better guidance and training for conducting landings in the vicinity of convective weather.

The Transportation Safety Board of Canada is issuing seven recommendations after finding that the crew of flight AF358, arriving in a severe thunderstorm, did not calculate a margin for error for the landing. The rapidly changing dynamics of the situation led to a "diminishing awareness" of the amount of runway available for the aircraft to stop, it says.

The TSB, which released its findings on 12 December, recommends establishing standards that would limit approaches and landings in convective weather. It also says pilots should be trained to make accurate estimates of the margin between landing distances available and those required before conducting approaches in deteriorating conditions.

Speaking during a briefing, the TSB's chief investigator into the accident, Real Levasseur, said: "We must give pilots better tools to let them know when they must not approach."

He said crews should be made fully aware of the distance an aircraft needs to land in different conditions, adding: "Information is available to pilots. However, in an unstable situation, it's not the time to leaf through manuals."

Flight AF358 had been arriving from Paris Charles de Gaulle on 2 August 2005. Two aircraft landing ahead of the Air France jet had already reported poor braking at Toronto.

As the A340 conducted its final approach to runway 24L, at a height of about 200ft (61m), the wind shifted and generated a tailwind component. This increased its ground speed and caused the aircraft to deviate above the glideslope.

It crossed the threshold 90ft above the ground, some 40ft higher than expected, and travelling at 145kt (268km/h), higher than the 140kt planned because of the tailwind. The jet then entered a heavy rain shower, which severely limited the crew's visibility.

While the crew opted to continue the landing, believing this would be safer than a missed approach into a storm, the aircraft floated and touched down at 148kt, some 3,800ft along 24L, leaving it with 5,300ft of remaining runway.

"It is clear that the pilots were aware of the landing distance available for runway 24L," says the investigators' report. "There is no indication that they had calculated the landing distances required for the arrival, nor are there any direct and specific Air France procedures that would require such calculations by the crew.

"This accident clearly shows the need for pilots to know the landing distance required by their aircraft for the conditions to be encountered at the expected time of landing, and to compare this figure to the length of the runway assigned for the landing. It is essential that both figures be known to enable crews to calculate the margin of error available so that they are better prepared to make the correct decision when they encounter deteriorating conditions.

"In this occurrence, the crew members realised at some time during the landing sequence that the landing was going to be long. Had they known that the margin for error was slim, or indeed non-existent, the crew would likely have executed a go-around."

The aircraft landed to the left of the centreline and the pilots delayed activating reverse thrust while they steered along the runway axis. Reverse thrust was not selected until 12.8s after landing and full reverse was not active until 16.4s after the jet touched down.

By the time full reverse thrust engaged, the aircraft was still travelling at 107kt with less than 1,200ft remaining before the end of the runway. It failed to decelerate in time and left the end of the runway at nearly 80kt, travelling about 1,000ft before coming to rest.

Although the aircraft was destroyed by fire, all 297 passengers and 12 crew survived, having evacuated the jet within 2min. Twelve passengers sustained serious injuries.

"Since the Air France accident, 10 large aircraft have gone off runways around the world in bad weather," says Transportation Safety Board of Canada chairman Wendy Tadros. "This is an unacceptable risk."

In addition to the recommendations on crew training and procedures, the TSB says it will recommend installing 300m runway-end safety areas at airports. It will also advise carriers to stress to passengers during safety briefings the importance of leaving baggage behind in an evacuation, after finding some travellers on AF358 stopped to retrieve personal items.

Source: Flight International