What happened
On July 24, 2004, a serious runway incursion occurred at Amsterdam Schiphol Airport during daylight hours. A tug driver, responsible for towing a Boeing 747-400 (registration PH-BFU) to a parking stand, contacted the tower to request permission to cross runway 24. At the same time, a Boeing 737 was positioned on the runway, preparing for departure.
Due to a communication error, the trainee air traffic controller granted the crossing clearance for runway 04-22, which the driver mistakenly applied to the active runway 24. As the tug proceeded across the intersection, it entered the active runway area. The tower controller, noticing the vehicle's position, immediately ordered the Boeing 737 to cancel its takeoff clearance. The aircraft, which had already begun increasing engine power, came to a rapid stop before it could depart.
The investigation
The investigation by the Dutch Safety Board (OVV) focused on the breakdown in communication and the failure of visual aids. Investigators found that the trainee controller provided an "anticipatory clearance"—granting permission to cross a runway before the vehicle's specific location or intent had been fully established.
Furthermore, the investigation examined the role of the stopbar at the S2 intersection. While stopbars are intended to prevent incursions, the investigation found that the light intensity had not been sufficiently increased following sunrise. The low visibility of the red lights, compounded by sunlight reflections, meant the stopbar failed to effectively signal the vehicle to stop.
Findings
Several contributing factors led to the incident:
- Incorrect clearance issuance: The controller provided permission to cross a runway without verifying the vehicle's exact position or the specific runway involved.
- Improper identification: The driver of the PH-BFU tow failed to properly verify the clearance, likely due to a habit of using standardized radio phrases which led to a subconscious acceptance of the incorrect runway designation.
- Failure of the stopbar: The stopbar at the intersection was not clearly visible because the light intensity was set too low for daylight conditions, and sunlight glare obscured the red lamps.
- Communication errors: The driver of a second tow, involving aircraft PH-CKC, also requested a crossing during the same sequence, adding complexity to the radio frequency.