What happened
On 4 April 2013, during a scheduled five-minute maintenance window at Changi Airport, a runway friction tester known as Rover 18 entered Runway 1 (02L/20R) without official clearance. The vehicle was part of a routine inspection process that had temporarily closed the runway.
While attempting to contact Changi Tower for permission to enter, the driver of Rover 18 was actually transmitting on the Seletar Airport frequency. Because the radio signal was distorted and fragmented, the driver mistakenly interpreted the garbled responses as authorization to proceed onto the runway.
Shortly after the runway was reopened for flight operations, the vehicle was still occupying the runway surface. A Changi Tower controller spotted the vehicle moving toward a taxiway and, after being unable to establish contact with the driver, was forced to instruct an approaching aircraft to execute a go-around when the vehicle was less than one nautical mile from touchdown.
The investigation
Investigators examined the radio communications and the technical setup of the friction testing vehicle. They found that the radio set in Rover 18 was tuned to 122.9 MHz (Seletar) rather than the required 121.9 MHz (Changi). This error likely occurred because the driver had used the same equipment at Seletar two days prior and failed to verify the frequency setting.
Further analysis revealed that the friction tester is operated by a single person who must simultaneously drive at 96 km/h, manage the friction measurement equipment, and monitor radio communications. The investigation noted that the radio set was positioned in a way that required the driver to move physically to operate it, making simultaneous driving and communication difficult. Additionally, high noise levels from the measurement equipment made clear audio reception challenging.
Findings
- The primary cause of the incursion was the driver entering the runway without valid authorization from Changi Tower.
- A frequency mismatch on the vehicle's transceiver prevented effective communication between the driver and Changi Tower.
- The driver misinterpreted distorted transmissions from Seletar Tower as permission to enter the runway.
- The short duration of the scheduled inspection window created time pressure that may have contributed to the failure to verify radio settings.
- The controller's decision to attempt contact with the vehicle before canceling the landing clearance delayed the go-around instruction.
Safety action
Following the incident, several measures were implemented to prevent a recurrence:
- The aerodrome operator installed a second radio set in the friction tester, with both Changi and Seletar frequencies pre-selected and clearly labeled.
- The radio equipment was relocated to the dashboard for easier access during operation.
- All Category 1 vehicles are now required to be equipped with Mode-S transponders to improve surveillance via the Advanced-Surface Movement Guidance and Control System (A-SMGCS).
- New procedures were adopted to schedule maintenance tasks within longer, 15-minute inspection slots to reduce time pressure.