What happened
On 27 July, a Boeing 737-400, registration G-DOCH, was performing a scheduled departure from Aberdeen Airport to London Gatwick. As the aircraft accelerated along the runway, the commander observed an AS332L Super Puma, registration G-PUMD, hovering at a height of approximately 30 feet directly in its path. The pilot immediately initiated a rejected takeoff, managing to bring the aircraft to a stop roughly 100 metres behind the helicopter.
The helicopter, which was conducting an air test following maintenance, had been hovering near holding point E2. The crew of the helicopter had requested clearance to enter the circuit and, following instructions from Ground Movement Control, transitioned from their hover into the path of the departing jet.
The investigation
The AAIB investigation focused on the sequence of communications between Ground Movement Control (GMC), the Tower controller, and the aircraft crews. It was established that the GMC controller had cleared the helicopter to taxi to E2 for a hover and subsequently issued a clearance for the helicopter to enter the circuit. However, the helicopter crew misinterpreted this clearance, believing they had been authorized to proceed into the runway area.
Investigators found that the Tower controller had issued the departure clearance for the G-DOCH with instructions for an immediate takeoff. While the controller checked the runway and saw the helicopter at the holding point, they did not perceive it as a threat to the departing flight. The investigation also noted that the helicopter crew was focused on instrument readings during their hover checks, which prevented them from monitoring the tower frequency for updated traffic information.
Findings
- The primary cause of the incident was the misinterpretation of the ATC clearance by the helicopter crew, who believed they were cleared to enter the circuit.
- The Tower controller failed to follow established procedures, which required repeating a 'hold position' instruction when issuing clearances that could be mistaken for takeoff permission.
- The GMC controller's view of the holding point was partially obstructed by a pillar in the control room, and the red color of the helicopter provided poor contrast against nearby buildings.
- The helicopter crew was experiencing fatigue due to recent extended working hours and intense flight schedules.
- The helicopter crew did not establish contact with the Tower controller or visually confirm the runway was clear before maneuvering over the active runway.