What happened
On 19 May 2025, a Malaysia Airlines Boeing 737-800, registration 9M-MLL, was taxiing at Singapore Changi Airport for a scheduled departure to Kuala Lumpur. After being cleared to line up on Runway 20C, the flight crew notified the Runway Controller (RWC) that they required an additional two minutes to prepare for departure. In response, the RWC cancelled the line-up clearance and reactivated the red stop bar lights at Holding Point T2.
The pilot-in-command incorrectly read back the cancellation instruction, stating they were "cleared line-up and wait," and continued taxiing toward the runway. Although the RWC attempted to instruct the aircraft to hold position, the transmission was truncated, and the crew responded with a second incorrect readback, claiming they were lining up to wait. The aircraft subsequently crossed the holding point, triggering a runway incursion alert on the airport's surface movement guidance system. The RWC, focused on directing an arriving aircraft to vacate the runway, did not intervene to correct the crew's error, and the aircraft eventually lined up on the runway.
The investigation
An investigation by the TSIB examined the radiotelephony exchange and the controller's decision-making process. The inquiry found that the RWC used a non-standard phraseology ("line-up clearance cancelled") rather than a direct imperative command. Furthermore, while the RWC noticed the incorrect readback and a visual alert for the stop bar violation, she chose not to issue a stop order, reasoning that the incursion had already occurred and her priority was managing the arrival of another aircraft.
Findings
- The primary cause of the incursion was the incorrect readback of instructions by the flight crew.
- The RWC's instruction lacked a direct imperative structure, which increased the risk of misinterpretation.
- The RWC failed to maintain positive control by not correcting the crew's second incorrect readback or ordering them to hold position.
- The RWC's attention was diverted by the need to manage an arriving aircraft vacating the runway.
- There was no evidence that the RWC's use of cough medication contributed to drowsiness at the time of the incident.