On 27 March 2002, a Fokker F28 being operated by Air Canada Regional Airlines (t/a Air Canada Jazz) on a scheduled night passenger flight from Toronto to Saint John, having made an uneventful procedural ILS approach to Runway 05 at destination, departed the slippery landing runway to the left shortly after touchdown in normal visibility conditions but regained it before coming to a stop. Aircraft damage was limited to minor cuts in the tyres of the right main and nose landing gear and damage to one runway edge light. There were no injuries to any of the occupants.
An Investigation was carried out by the Canadian Transportation Safety Board. It was established that after the nose gear had touched down, the aircraft had started to drift uncontrollably to the left and the left main wheels had departed the side of the runway for a distance of approximately 275 metres before regaining the paved surface. The left main gear track was found to have been just under five metres from the runway edge at its furthest point. It was noted Runway 05, the incident runway, was asphalt surfaced, 2130 metres long and 60 metres wide. Air traffic communications between the ‘certified uncontrolled’ airport at Saint John and the aircraft had been in the hands of the airport ‘Flight Service Station’ (FSS) personnel.
The weather conditions being reported shortly before the aircraft landed were a wind velocity of 140° / 9 knots in light snow with visibility of 1400 metres and a temperature of MS02. The effect of a near zero surface temperature on the minimal snow covering was to be conducive to the incidence of slush on the runway rather than dry snow grains.
FDR data showed that the Flap 42 landing had been made near the runway centreline at a speed compatible with the calculated Vref and just three degrees to the right of the runway heading. After nosewheel contact, the aircraft heading had increased to 065 degrees, while the aircraft had drifted towards the left side of the runway. It was considered that the drift was probably a result of the combined effect of the crosswind from the right and the small amount of pre-existing left drift at touchdown. However, the investigation could not determine the extent to which either contributed.
The flight crew had attempted to correct the ground path of the aircraft by using rudder and nosewheel steering inputs but despite an increasing heading to the right, the aircraft continued to drift toward the left and off the runway. Partial control of the aircraft had been regained as the left main gear regained the paved surface but steering response had still been ineffective with the aircraft continuing to slide with the nose slewed to the right. The flight crew had shut down the left engine at about 60 KIAS after which the aircraft had remained aligned with the runway centreline. It was stopped and then taxied to the ramp with the flight crew advising the FSS that the braking action on Runway 05 was very poor and that they “believed the aircraft had come very close to the runway edge”. It was subsequently confirmed that the aircraft had left the runway, which at the time of landing had not been cleared of a light and recent snow covering of about 6mm on a previously dry and bare surface. It was noted that the flight crew had declined the offer of a “centreline sweep” of the runway prior to their landing.
At the time if the occurrence, runway surface friction in Canada was being measured using a decelerometer. This was used as a means to report values for friction on a linear scale in increments from 0 to 1, with 1 being equivalent to the theoretical maximum decelerating capability or friction on a dry runway. These values were referred to as the Canadian Runway Friction Index (CRFI). However, this measurement is not valid on slush-covered runway such as the one which prevailed and the most recent value was in any case not passed to the crew prior to landing.
The Investigation concluded that the cause of the excursion was that:
“The poor friction characteristics of the runway, due to slush contamination, did not allow the crew to correct the aircraft's ground track after touchdown and the aircraft slid off the side of the runway”.
Following the occurrence, the aircraft operator indicated that it would take the following steps to reduce the likelihood of further runway excursions in conditions where slush might be encountered:
- Publish a Flight Operations Bulletin advising flight crews of the potential for CRFI reports to become invalid quickly after the reading was taken, particularly during changing weather conditions where temperatures are at or near the freezing level and surfaces are contaminated with snow, slush, ice or standing water, or where precipitation or visible moisture is present during the approach and landing.
- Direct crews to consider delaying a landing and consider the validity of CRFI reports only after the runway has been swept giving due consideration to depth of contaminates between the time of the CRFI measurement and the landing. CRFI reports taken prior to the removal of contaminants from the runway should be considered unreliable and extreme caution should be taken prior to landing in such conditions.
- Require crews to confirm the type of runway de-ice treatment used prior to the CRFI being taken on ice-covered runways.
- Include a review of winter operations, with emphasis given to runway conditions, in recurrent ground school and simulator programs.
- Add discussion on aircraft directional energy after break out and prior to landing on contaminated runways to recurrent ground school and simulator training programs.
The Final Report of the Investigation was authorised for release on 17 December 2002 and may be seen in full at SKYbrary bookshelf: TSB Aviation Investigation Report A02A0038