On 12 March 2013, an Airbus A320 (TS-IMC) being operated by Tunisair on a scheduled passenger flight from Djerba to Paris Orly landed normally on runway 08 at destination in day Visual Meteorological Conditions (VMC) but was unable to clear the runway after encountering a deterioration from the braking effectiveness encountered earlier on the snow and slush-covered surface. An overrun at taxi speed occurred and the aircraft came to a stop with the NLG off the runway but the MLG still on it. Passengers were disembarked to ground transport using steps positioned at the left hand rear door.
The aircraft positioned partly off the runway after the overrun showing the depth of contaminant on the runway at its end. Reproduced from the Official Report
An Investigation was carried out by the French BEA.
It was established that the Automatic Terminal Information Service (ATIS) which had been obtained as the destination was approached advised that runway 08 was the only active runway and was covered with dry snow and that it should be vacated either via runway 02/20 (approximately at the midpoint) or taxiway at the runway end. ATC then advised that braking action on the runway was "medium to poor". The crew were aware that there was slush on the runway. During the approach, the crew discussed the risk of a runway excursion and confirmed the previously-advised braking action. The First Officer was PF. The autobrake was set to 'medium' and the Reference Speed (Vref) of 137 KIAS was set. The final approach was stabilised and the landing normal. During the landing roll, the Captain took control in accordance with the operator’s procedures with the intention of vacating via runway 02/20. As the aircraft decelerated through 70 knots groundspeed, the autobrake was disconnected and shortly afterwards the thrust reversers were also stowed.
As the aircraft approached the intended intersection turn off at just over 40 knots groundspeed, the controller asked the crew to vacate at the end of the runway not the intersection, a further 1700 metres. The aircraft continued as instructed and the Captain slightly increased thrust so that the ground speed increased to and stabilised at around 60 knots. Shortly after reaching a position 500 metres from the end of the runway, braking re-commenced but the effect, even with increased brake pressure, was not enough to reduce the speed and the end of the runway was approached at a ground speed of 35 knots. The Captain then applied the parking brake and tried to control the direction using the rudder pedals. The overrun occurred at a groundspeed of 17 knots and the aircraft subsequently stopped with the MLG still on the paved surface. It was apparent that an emergency evacuation was not required and after a delay of forty-five minutes, passengers were disembarked to ground transport using steps placed at the rear left hand door. After the overrun, the Captain described the braking action towards the end of the runway as "very, very poor".
It was found that prior to the landing, there had been "continuous and variable snowfall since 0800 local time with a generally N to NNE surface wind of around 10knots. From 15 minutes prior to the touchdown, "precipitation occurred in the form of continuous light snow, with a surface wind from 020 degrees at about 6 knots".
Airport Operator ADP advised that the current braking action communicated by them to ATC for the full length of runway 08 at the time of the landing and overrun was "medium". Airbus used the recorded braking performance over the final third of the runway to determine what the actual braking action had been and found that it had been "medium to poor" - the same as had been confirmed by ATC six minutes before landing.
The Investigation noted that there was a Quick Reference Handbook (QRH) memory procedure for "loss of braking" which required the crew, regardless of the speed it occurs, to fully activate the thrust reversers and apply maximum brake pressure. If there is still no braking, the procedure requires the application of the parking brake several times in succession.
The Findings of the Investigation were as follows:
- The crews that landed before the Tunis Air flight had estimated the braking efficiency to range between “medium” and “medium to poor”. These indications were observations provided for information purposes only and did not concern the condition of the end of the runway.
- The crew correctly managed the landing roll in order to exit the runway at mid-point. They were not concerned by the controller’s request to roll to the end of the runway (W31) as they referred to the braking efficiency observed up to then.
- Frequent takeoffs and landings on the same runway tend to limit the accumulation of contaminant on the rolling portion used by aeroplanes. However, the ends of runway, being less used, become contaminated more quickly and can be very slippery. The ATC service should be reminded of this to assist them in managing runway exits.
- The use of measuring equipment is highly disadvantageous from an operational perspective as it requires closing the runway for about twenty minutes. However, no remote real-time measuring equipment is available to date. Nevertheless, the fact that the last third of the runway was not properly cleared of snow represented a potential risk of overrun, especially in case of an aborted takeoff.
- The aeroplane only partially overran the runway and the incident might have been avoided by applying the “Loss of Braking” procedure.
The Conclusions of the Investigation were that:
- The inability to measure runway adherence in real time did not to allow the uneven runway contamination to be detected.
- This led to the crew’s and controllers’ degraded perception of braking conditions at the end of the runway, resulting in the overrun.
- The failure of the crew to apply the available 'Loss of Braking' procedure may have contributed to the outcome.
The Final Report was published in English translation on 24 September 2014 following initial publication in French on September 2014. No Safety Recommendations were made.