Background
The flight was a periodic training session with a Training Captain and three pilots. Two full-stop landings were planned. The aircraft had made an uneventful first landing on a wet runway, using about half the available distance. After a crew change, the aircraft taxied to the holding point of Runway 27. Light snow had started to fall but was not settling.
Account of the Incident
The crew initiated a missed approach from an NDB/DME approach when not in visual contact with the airfield. The commander then decided to conduct an ILS approach to land. He assumed the runway condition was unchanged from the earlier landing, as ATC had not advised of any deterioration. Landing weight was 49,650 lbs, with required landing distances for a wet runway calculated as 5,515 feet. The commander reported touching down at an acceptable distance and speed for a wet runway. Thrust reversers were deployed and wheel braking applied. When deceleration was less than expected, the commander confirmed full reverse and applied his own brakes. The aircraft decelerated slowly and overran the runway near the centreline at an estimated 10 knots. It came to rest with main wheels on firm grass about 2 metres beyond the paved area; the nosewheel sank into soft ground. The commander later noticed significant slush on the runway and snow-covered grass. Several airport personnel reported that the aircraft touched down beyond the normal touchdown zone. The commander acknowledged the final approach was slightly high and fast, and the touchdown was light. He believed the runway was more contaminated than earlier and that aquaplaning may have occurred; minor aquaplaning evidence was seen on the tyres, and no antiskid juddering was felt.
Meteorological Conditions
At 1620 UTC, METAR reported surface wind 360°/3 kt, visibility 1,200 metres, snow, scattered cloud at 400 feet, broken cloud at 800 feet, temperature 1°C, dew point 0°C. A special METAR at 1634 UTC showed similar conditions with visibility 1,500 metres.
Runway Inspections
Snow had been falling since about 1530 UTC. A pre-night inspection at 1600 UTC found Runway 27 wet but no settled snow, though snow was settling on taxiways and Runway 04/22. At 1624 UTC, the Senior Airport Fire Officer (snow coordinator) decided to conduct his own inspection. He was at holding point Alpha 2 waiting to enter the runway when the Gulfstream landed. After the overrun, he entered the runway and assumed command. A post-incident inspection at about 1650 UTC found insignificant contamination on Runway 27, but deposits accumulating on the north end of Runway 04 and taxiways. A Grip Tester run at 1727 UTC rated braking action on Runway 27 as Medium to Good.
CAA Comment
The CAA stated that because a runway inspection was deemed necessary due to snow, the Aerodrome Controller should have at least warned the Gulfstream's pilot of the snow's existence, especially since the inspection could not commence before landing.
Conclusion
Although the runway inspection 20 minutes after the incident showed insignificant contamination, it is possible that snow or slush deposits had formed after the 1600 UTC inspection and were present at landing, reducing braking action. This, combined with a slightly high and fast final approach and a light touchdown outside the normal touchdown zone, would have reduced the crew's ability to stop within the remaining runway.