On 23 December 2009, a Boeing 737-800 being operated by Irish airline Ryanair on a scheduled passenger flight from Dublin to Prestwick left the end of the destination runway in normal daylight visibility and the landing gear sunk into the adjacent wet grass after an attempt to brake on the icy surface prior to turning onto the designated exit taxiway was unsuccessful. The uninjured occupants left the aircraft via the forward airstairs onto the grass and then moved across to the paved surface of the taxiway and runway.
An Investigation was carried out by the UK AAIB. It was established that, with the aircraft commander as PF, the approach to and landing on the 2987 metre long wet runway were found to have been normal. Braking Action had been pre-notified as ‘medium-good’ throughout. Taxiways and Aprons were pre-notified as ‘extremely icy’. With the aircraft unable to vacate at the usual intermediate point and the aircraft substantially decelerated, it was allowed to ‘roll’ to the end. When manual braking was applied at a recorded groundspeed of 42 knots, it was ineffective and, with the end of the runway approaching, the aircraft commander attempted to turn the aircraft 90° to the left onto the exit taxiway so as to avoid a runway excursion. The nose of the aircraft slewed 45° to the left but the wheels continued to track along the runway and the aircraft was found to have slid off the paved surface onto the grass at a recorded groundspeed of 24 knots some 30 seconds after manual braking had been initially attempted. It came to a stop after a further 20 metres travel.
It was noted that photographs of both the runway and the taxiway taken at the time appeared to show a glazed reflective surface, suggesting the presence of ice. No evidence was found of any technical problem with the braking systems of the aircraft.
Prior to the landing, a de-icing run had been carried out over the middle 30 metres of the 45 metre wide runway but this was found to have been made at an application rate only suitable for anti-icing and it was concluded that it was likely to have been of limited effectiveness. Although it could not be shown from FDR data whether the aircraft maintained the centreline of the runway throughout the landing roll, it was considered unlikely that it went outside the 30 metre treated strip.
It was observed by the Investigation that there had been no attempt to re deploy reverse thrust, “probably because it is an unusual action once cancelled”. It was considered that such action may have had some beneficial effect despite the fact that it would have taken a few seconds for engines at idle power to spool up.
It was noted that the crew of a preceding aircraft, which had landed on the same runway four minutes earlier, had not reported any difficulty with the braking action and no reason for this difference was established.
As a result of the investigated event, the airport operator was found to have made a number of procedural improvements with a particular focus on runway anti-icing and de-icing operations. The aircraft operator involved was also noted to have added a training module on operations to or from slippery runways to its recurrent training programme. The AAIB did therefore not consider it necessary to make any formal Safety Recommendations.
The Final Report of the Investigation was published on 14 October 2010 and may be seen in full at SKYbrary bookshelf: AAIB Bulletin: 10/2010 EW/G2009/12/14