What happened
On December 1, 2001, at Zurich Airport, an Airbus A319, operated by TAP Air Portugal with registration CS-TTM, entered a dangerous situation on the ground while taxiing toward Runway 28. The aircraft was taxiing via Taxiway Echo, following instructions from the Apron controller to hold short of the runway. During the taxi, the crew was also informed they were following a Swissair Airbus 330.
As the A3 and A319 approached the intersection of Taxiway E and Runway 28, the crew transitioned from Apron frequency to Zurich Ground. Despite receiving an explicit instruction from the Ground controller to hold short of Runway 28—which the crew correctly read back—the aircraft continued past the red stop bars. The aircraft's nose eventually reached the runway shoulder.
Simultaneously, a Crossair Saab 2000, registration HB-IYG, was in the middle of its takeoff roll on Runway 28. The Aerodrome Controller observed the A319 crossing the stop bars and realized the departing Saab 2000 could not safely abort its takeoff. The takeoff proceeded, and the pilot of the Saab 2000 noted the approaching aircraft but assumed it would stop before the runway.
The investigation
Investigators examined the communications between the various controllers and the flight crews. The investigation established that the Ground controller and the Apron controller both observed the incursion. The investigation also reviewed the automated recording of the stop bar status, which showed the red stop bars had been activated specifically for this movement.
Findings
- The primary cause of the incident was a short-term loss of attention by the flight crew of the CS-TTM due to an internal disagreement regarding radio frequency management.
- The crew failed to adhere to the explicit instruction to hold short of Runway 28, despite a correct read-back of the instruction.
- The use of certain phraseology by the Apron controller, specifically informing the crew they were "number two behind" another aircraft, was noted as potentially confusing, though not the direct cause of this specific event.
- The taxiway naming convention, where a single name (Taxiway Echo) spans both sides of a runway, could lead pilots to believe they have clearance to proceed through the intersection.
Safety action
- A recommendation was made to review taxiway naming conventions so that taxiways crossing runways carry different identifiers.
- It was recommended that controllers avoid using phraseology such as "you are number two behind" to prevent potential misinterpretations.
- A suggestion was made for Apron controllers to reinforce "hold short" instructions when instructing aircraft to switch to Ground frequency.