What happened
On 31 October 2004, an Emirates Airbus A330-243, registration A6-EKU, was on final approach to runway 14 at Zurich Airport. Due to turbulence caused by north-easterly winds, the flight crew encountered an unstabilized approach and initiated a go-around just feet above the ground.
Simultaneously, a Swiss International Air Lines AVRO 146-RJ100, registration HB-IXU, had been cleared for takeoff on runway 10. Upon noticing the go-around of the Airbus, the aerodrome controller issued an instruction to the AVRO 146 to reject its takeoff. The crew of the AVRO 146 initially did not react to the first command but successfully aborted the takeoff at approximately 100 knots, shortly before reaching its decision speed of 115 knots. Radar data indicated that had the takeoff continued, the two aircraft would have converged within approximately 390 meters.
The investigation
The investigation examined the actions of the air traffic control (ATC) unit, which was staffed by a trainee supervised by an assessor at the time of the incident. Investigators reviewed radar recordings, cockpit voice recordings, and radio communications. The inquiry focused on the separation procedures used for crossing runways and the specific instructions issued by the aerodrome controller during the critical phase of the aircraft's missed approach.
Findings
- The aerodrome controller granted takeoff clearance to the aircraft on runway 10 while the Airbus was still only 0.6 NM from the threshold of runway 14.
- The existing Skyguide procedures allowed for takeoff clearances on runway 10 once an aircraft had passed the runway 14 threshold, a rule that failed to account for the possibility of a late go-around.
- The separation procedures were found to be incomplete and difficult to apply, as they did not consider the specific performance characteristics or the potential for unstabilized approaches due to local topography and wind.
- The instruction to reject a takeoff was used as a standard method for traffic separation rather than as an emergency measure.
Safety action
Following the incident, the investigation highlighted a safety deficiency in using takeoff rejection as a routine tool for separation. It was noted that ATC should avoid modifying standard missed approach flight paths during high-workload phases. The investigation led to a safety recommendation for the Federal Office of Civil Aviation to ensure that Zurich Airport develops operational concepts that guarantee required separation between aircraft performing go-arounds and those taking off on crossing runways.