Overview
On 4 April 2013 at 1349 hours Singapore time, Changi Airport Runway 1 (02L/20R) was closed for a five-minute daily inspection by the Airside Safety Inspection Team (ASIT), consisting of vehicles with callsigns Rover 34, Rover 35, and Rover 39. A surface friction tester, callsign Rover 18, had been scheduled to perform a friction test in conjunction with the closure. However, Rover 18 departed its office at 1350:37, after the runway had already been closed for about one minute.
Sequence of Events
Rover 18 attempted to contact Changi Tower on 121.9 MHz to request permission to enter the runway. The transmissions were not received by Changi Tower or the other ASIT vehicles. Instead, they were received by Seletar Tower, approximately 16 km to the west, on 122.9 MHz with severe distortion. Seletar Tower could only hear disjointed words and could not identify the caller, nor did it issue any clearance. Rover 18, hearing only distorted transmissions, did not realize they were from Seletar Tower. At 1353 hours, despite lacking authorization, Rover 18 entered Runway 1 via Taxiway W10 at the southern end and proceeded northbound.
At 1355:07, Rover 34 reported that the ASIT had left the runway, and the runway was re-opened. Rover 18 was still on the runway, having passed Taxiway W3 and entered the displaced threshold area at the northern end. Shortly thereafter, Changi Tower cleared an aircraft to land on Runway 20R. Meanwhile, Rover 35 alerted Rover 34 that Rover 18 was still on the runway. Rover 34 attempted to contact the tower but the frequency was busy, and calls to Rover 18 went unanswered.
Communication Issues
Changi Tower spotted Rover 18 moving southbound near Taxiway W4. Over 43 seconds, the tower tried to contact the vehicle without response. The landing aircraft continued its approach, unaware of the vehicle. At 1357:47, with the aircraft about 0.89 nautical miles from touchdown, the tower instructed it to go around. Afterward, the tower tried for another 44 seconds to reach Rover 18, but the driver did not hear the calls. Rover 18 eventually exited the runway and established communication with Changi Tower at 1359:54.
Aftermath
The investigation revealed that Rover 18's radio had been tuned to 122.9 MHz instead of 121.9 MHz, causing transmissions to be received by Seletar Tower. The poor radio quality compounded the confusion. No injuries or aircraft damage were reported. The Air Accident Investigation Bureau of Singapore classified the occurrence as an incident.
Safety Actions
Following the incident, the aerodrome operator implemented actions to prevent recurrence, including reviewing radio procedures and reinforcing the requirement for positive clearance before entering runways.