What happened
On 23 December 2009, a Boeing 737-800, registration EI-DHD, was operating a scheduled passenger flight from Dublin to Glasgow Prestwick Airport. During the approach, the crew noted a brief disturbance in the localiser signal. The aircraft touched down normally on Runway 31 at 0846:50 hrs.
Following instructions from Air Traffic Control, the crew intended to vacate the runway at the end of the strip via Taxiway J, as Taxiway K was closed. The commander had previously cancelled the autobrake at approximately 100 kt and selected reverse thrust at 60 kt. As the aircraft approached the end of the runway, the pilot applied the brakes, but they appeared to have no effect. Despite increasing brake pressure to the maximum, the aircraft failed to decelerate sufficiently. In an attempt to avoid a runway excursion, the commander attempted a 90-degree left turn onto the taxiway. This maneuver caused the nose to slew 45 degrees to the left, and the aircraft slid off the paved surface onto the grass at a speed of 24 kt. There were no injuries to the 129 passengers or 6 crew members, and no damage was sustained by the aircraft.
The investigation
Investigators examined flight data recorder and cockpit voice recorder data, which confirmed the sequence of braking applications. CCTV footage from the airport showed a glazed, reflective surface on the taxiway, indicating the presence of ice.
The investigation also reviewed the airport's winter maintenance. A SNOWTAM issued earlier that morning had warned of frozen ruts on Runway 13 and extremely icy taxiways and aprons. While a de-icing run had been performed on the runway earlier that morning, the application rate used was only appropriate for anti-icing, which likely provided limited effectiveness for removing existing ice. Furthermore, while the preceding aircraft had landed only four minutes prior without reporting issues, the surface conditions at the end of the runway were found to be icy.
Findings
- The aircraft's braking effectiveness failed during the second application of the brakes.
- The surface at the end of the runway was icy.
- The de-icing application rate used by the airport operator was insufficient for de-icing purposes.
- The co-pilot did not communicate the specific details regarding the extremely icy taxiways and apron to the commander during the approach.