On 27 July 2000, a Boeing 737-400 being operated by British Airways on a scheduled passenger flight from Aberdeen to London Gatwick made a high speed rejected takeoff in normal daylight ground visibility upon sighting an AS332 being operated by CHC Scotia on an Air Test hovering over the upwind end of the take off runway. The 737 came to a stop approximately 100 metres before reaching the position of the helicopter.
An Investigation was carried out by the UK AAIB.
It was established that the air test detail being accomplished by the AS332 helicopter, which had a ground engineer in board as well as the two pilots, involved an initial period in the hover before departure into the local circuit for the remaining items of the test. With the First Officer as PF, it had been cleared by GND to carry out the hover requirement after hover taxiing to the E2 holding point situated at the upwind end of the active runway 16. Whilst en-route to the holding point, GND had passed the departure clearance and instructed the helicopter to change to TWR but thus was neither acknowledged nor actioned. After a couple of minutes in position, and with the hover test complete, the helicopter checked in with TWR just after the 737 had been given take off clearance. As the helicopter was being told to return to their previous position, the 737, with the First Officer also acting as PF, rejected take off after the conflict was seen ahead and the aircraft commander called ‘stop’ at a speed of 100 KIAS.
The Investigation noted that the GND controller had failed to add a ‘hold position’ reminder to end of his transmission of the departure clearance to the helicopter. This procedure had been highlighted for local application via ‘Safety Notices' based on text which had been added to the UK CAA ATC Procedures Manual CAP 493 in June 2000 following an incident in which an aircraft had taken off with only a departure clearance and narrowly missed colliding with a light aircraft on an intersecting runway at Birmingham in 1999 which read:
"When, after an aircraft has been instructed to hold clear of the runway, a clearance message is passed which might be misinterpreted as permission to take-off, the instruction to hold should be repeated as part of the message."
Following the investigated incident, the airport ATC manager issued another reminder to that effect and also decided to restrict all hover checks to two designated locations neither of which was also a runway holding point.
It was noted that CHC Scotia’s internal investigation of the incident had led to the following changes to Company procedures:
- Helicopters should land after an extended period hovering at a hold and requests for departure clearances should be made whilst the helicopter is on the ground.
- Management should re-examine the aspect of extended consecutive work periods for crews with a view to reducing their susceptibility to tiredness.
- The operator should examine crew rest facilities.
- An acceptable area, clear of the runway holding points, should be identified for the hover testing of helicopters.
The Conclusion of the Investigation was follows:
Since the controller did not repeat the instruction to hold as part of the clearance message it was capable of being misinterpreted as permission to take off. Helicopters at the hold at E2 are not only difficult to see from the VCR but it is also difficult for the GMC controller to see whether they are in the hover or on the ground with rotors running.
The crew of the helicopter assumed they had been given take off clearance possibly because the helicopter was at the hold but 'in flight' (i.e. hovering) at the time the clearance was passed. Having misinterpreted the clearance the crew did not make contact with the tower controller or visually ascertain that the runway and approach were clear before they entered the active runway.
The Final Report of the Investigation was published in May 2001. No Safety Recommendations were made.
Further Reading/Related Articles