What happened
On 18 June 2010, a serious airprox incident occurred at Zurich Airport involving two aircraft on intersecting runways. The first aircraft, a Thai Airways International Airbus A340-600 (registration HS-TNA), was cleared to take off from runway 16. Almost simultaneously, a Blue Islands ATR42-320 (registration G-DRFC) began its takeoff roll on runway 28.
The danger was identified 15 seconds later when a third aircraft, a British Airways flight holding near the threshold of runway 2 and 28, alerted air traffic control that two aircraft appeared to be taking off at the same time. Upon receiving this information, the controller ordered the Blue Islands crew to abort their takeoff. The crew successfully vacated the runway, while the Thai Airways flight continued its departure.
The investigation
The investigation examined the radio communications, the technical performance of the airport's conflict alert system, and the visibility of the aircraft from the control tower. Investigators analyzed recordings from the emergency frequency and the RIMCAS conflict alert system.
Technical analysis revealed that while the crew of the G-DRFC had acknowledged a takeoff clearance, this transmission was not heard by the air traffic controller. The investigation found that the specific placement of radio receivers at the airport caused the signal to be suppressed. Furthermore, the investigation looked into why the air traffic controller did not visually detect the unauthorized takeoff roll on runway 28 and why the automated conflict alert system failed to provide timely warning.
Findings
- The primary cause was that the crew of the G-DRFC initiated a takeoff roll without a valid clearance.
- The crew of the G-DRFC failed to notice the takeoff clearance readback provided by the HS-TNA crew.
- Radio signal suppression occurred because the automatic selection of the best signal at the receiver location caused the controller to miss the critical readback.
- The air traffic controller did not observe the start of the takeoff roll on runway 28.
- The airport's conflict alert system was not configured effectively to prevent this specific type of conflict.
- The high-traffic, complex operation on intersecting runways left very little margin for error.