What happened
On October 17, 2017, a Cessna 510 was performing an IFR approach to land on runway 24 at Sylt Airport. The flight originated from Diepholz and carried a crew of two and two passengers. Due to strong westerly winds, the crew had transitioned from an ILS approach for runway 32 to a visual approach for runway 24.
Simultaneously, a ground vehicle was operating on runway 14. The driver, tasked with cleaning weather measurement equipment, requested clearance to proceed from taxiway Foxtrot via Lima to the old runway 03. The air traffic controller granted this clearance but specifically instructed the driver to stay clear of the safety area of runway 24.
As the Cessna 510 was touchdown on runway 24, the ground vehicle entered the intersection of runways 14 and 24. The controller, noticing the conflict only as the aircraft was over the threshold, instructed the driver to "drive on, quickly drive on!" The vehicle crossed runway 24 without explicit crossing authorization. The aircraft crew noted the vehicle a few hundred meters after landing but determined there was no immediate danger and completed the landing.
The investigation
The BFU investigation focused on the communication between the controller and the driver, as well as the intended path of the vehicle. The investigation established that the controller assumed the vehicle would turn left from runway 14 onto the decommissioned runway 12/30, a route that would not require crossing runway 24. However, the driver intended to follow a path that necessitated crossing runway 24.
Investigators found that the driver's intended route was constrained by heavy vegetation on the old runway, making a direct transition from runway 14 to runway 12/30 difficult for standard vehicles. Furthermore, the investigation noted that the aircraft and the vehicle were operating on different radio frequencies, preventing the driver from hearing the arrival of the aircraft.
Findings
- The primary cause of the incident was the ground vehicle crossing runway 24 without a valid clearance while the Cessna 510 was landing.
- A significant misunderstanding occurred between the controller and the driver regarding the permitted route; the controller's instruction to stay clear of runway 24 was interpreted differently by the driver.
- The driver failed to stop before runway 24 despite not having an explicit crossing authorization.
- The driver was unable to monitor aircraft movements because the vehicle was operating on a different frequency than the aircraft.
- The lack of unique identifiers for weather measurement equipment contributed to the confusion regarding the intended taxi route.
- The taxiway hold lights at the airport do not deactivate during crossing clearances, which can diminish their safety function.