What happened
On 16 January 2013, a Britten-Norman BN2B-20 Islander, registration G-SICA, was performing a commercial cargo flight departing from Runway 20 at Lerwick/Tingwall Airport. As the takeoff roll commenced, the aircraft began an uncontrollable drift to the right. The pilot attempted to counteract this movement using nosewheel steering and differential braking, but was unable to maintain the centerline. Consequently, the commander closed the throttles and aborted the takeoff at an estimated speed of between 10 and 20 knots. The aircraft slid approximately two metres off the paved runway surface before coming to a halt. While the aircraft sustained no injuries to the crew and no damage to the airframe, a frangible runway edge light was broken during the excursion.
The investigation
The investigation examined the runway conditions and the operational procedures in place at the time. At the time of the incident, the runway surface was contaminated with ice. The air temperature was recorded at 0ºC, with winds remaining variable at less than 5 knots. The investigation considered the possibility that sunlight had caused the existing ice on the runway to begin thawing, potentially creating a glazed surface.
Further inquiry revealed that the aircraft operator had recently requested that the airport cease treating icy or compressed snow runways with sand to prevent the risk of sand ingestion into turbine engines. The investigation also noted that the runway had been used for a landing within the hour prior to the incident.
Findings
- The primary cause of the excursion was the uncontrollable drift to the right caused by the untreated, ice-contaminated runway surface.
- The pilot's inability to correct the drift was attributed to the lack of friction on the icy surface.
- The airport's decision to stop using sand for runway treatment contributed to the contaminated state of the runway.
Safety action
- The aircraft operator has updated its operating procedures to prevent flights from using runways that have not been treated for ice or packed snow.
- The Airport Authority has reversed its previous decision regarding sand application, agreeing to sweep the runway provided that turbine-powered aircraft operations are active.