What happened
On 30 March 2011, a Sikorsky S-92A, registration G-IACC, was being ground taxied to a parking position at Scatsta Airport in the Shetland Islands. The taxiing was conducted under the direction of a marshaller. Upon reaching the designated parking spot, the co-pilot, acting as the pilot monitoring, called out the standard checklist items for brakes and lights.
As the aircraft came to a halt, the commander, acting as the pilot flying, intended to engage the parking brake. However, instead of reaching for the parking brake handle, the commander inadvertently raised the collective control lever. This action applied pressure to the foot brakes and caused the helicopter to lift approximately six feet off the ground with a slight roll to the left. The commander immediately released the lever, but because the collective trim system was not engaged, the lever returned to its neutral position, causing the aircraft to descend rapidly and strike the ground with significant force.
The investigation
The investigation examined the mechanics of the collective trim system and the sequence of cockpit actions. It was established that the collective lever on this aircraft type features an electromagnetic brake. When the control trigger is released, the brake engages, holding the lever in its selected position. In this instance, the lever was in a position that allowed it to move freely.
Following the hard landing, the aircraft was taxied to the North Aprons for inspection. The examination revealed structural deformation in two areas of the fuselage and a crack in one of the left main landing gear wheel rims, which had also resulted in a deflated tyre.
Findings
- The primary cause of the accident was the unintentional application of the collective lever in place of the parking brake handle.
- The commander's action caused the helicopter to become airborne and subsequently land heavily.
- The collective trim system allowed the lever to move rapidly when the trigger was released, contributing to the heavy impact.