What happened
On 28 November 2020, a B737-300 freighter, registration PK-YGW, was taxiing at Singapore Changi Airport for a scheduled flight to Jakarta. While proceeding toward Runway 02C, the aircraft crossed the runway holding position at Taxiway E11 without receiving authorization from Air Traffic Control (ATC). The incursion was detected by the airport's Microwave Barrier Detector system, which alerted the Runway Controller. At the time, another aircraft was on approach to land. The controller immediately instructed the crew to vacate the runway via Taxiway E10, which the crew performed successfully. No injuries or aircraft damage occurred, and the flight was subsequently cleared for takeoff.
The investigation
The investigation focused on why the crew entered the runway without clearance and why the error was not caught by the monitoring pilot or the augmented crew member. Investigators examined the communication between the flight crew and ATC, noting that while the Runway Controller instructed the aircraft to hold short, the Pilot Monitoring (PM) provided a readback that omitted the specific "hold short" instruction. The controller did not correct this discrepancy.
Further examination of the cockpit environment revealed that the Pilot Flying (PF) was performing a Before Take-off (BTO) checklist. During this process, the PF did not observe the illuminated red stop bar lights or the runway guard lights. The investigation also looked into the crew's fatigue levels, noting that the flight was the final sector of a six-sector duty day, with the crew having been on duty for over 13 hours.
Findings
- The primary cause of the incursion was the PF assuming clearance had been granted to enter the runway.
- The crew's reliance on memory for verifying takeoff clearance, rather than having it as a formal checklist item, contributed to the error.
- The Pilot Monitoring was focused on completing the BTO checklist and had not yet announced its completion, preventing a timely warning to the PF.
- The augmented flight crew member was present but was not assigned specific duties, leaving a valuable resource unutilized.
- Potential fatigue was a factor, as the crew had been on duty for a significant duration.
- Low traffic volume and a lack of radio transmissions from other aircraft may have reduced the crew's situational awareness regarding arriving traffic.
Safety action
Following the incident, the ATC service provider conducted safety briefings for controllers to improve methods for informing pilots of upcoming arrival traffic. Additionally, the investigation prompted several recommendations for the aircraft operator to review checklist procedures, crew rostering, and the use of augmented crew members.