Incident Overview
At approximately 0930 hours local time on 15 July 2010, a runway incursion occurred at Singapore Seletar Airport involving a Piper 28A (registration 9V-BON) and a Cessna 172 (registration 9V-FCI). The incident was classified as an incident by the Air Accident Investigation Bureau of Singapore.
Sequence of Events
The Cessna 172 was holding at the northern end of Runway 03/21, awaiting take-off clearance from the air traffic control tower for departure on Runway 21. Simultaneously, the Piper 28A was taxiing towards the holding area on Taxiway W2, with a student pilot on his twelfth solo flight. The student pilot had just completed a check flight and his instructor had disembarked at the control tower. The student pilot expected to be instructed to backtrack to the northern end of Runway 03/21 for take-off, in accordance with the flying school's standard operating procedures.
After the Tower Controller (TC) issued a take-off clearance to the Cessna, both the Cessna and the Piper read back the clearance at the same time, resulting in a cross communication where only the Piper's readback was heard by the TC. Consequently, the Cessna began its take-off roll while the Piper also started moving towards the runway.
The TC, aware that the readback came from the Piper, observed the Piper moving towards the runway. After a delay of approximately 10 seconds, the TC cancelled the take-off clearance for the Cessna. Both aircraft stopped about 100 m apart. There was no injury to any person and no damage to either aircraft.
Student Pilot's Account
The student pilot reported that after hearing the take-off clearance, he assumed it was for him, although he found it odd that the tower did not ask him to backtrack. He read back the clearance with his callsign and waited for a correction that never came. He then proceeded with caution, applying brakes upon seeing an aircraft on the runway. The Piper's nose had just crossed into the runway area when it stopped. The student pilot stated he was aware he should request clarification if doubtful, but due to the hot weather, he wished to take off as soon as possible.
Tower Controller's Account
The TC stated she scanned the runway and heard the Piper's readback. She had two options: correct the student pilot or cancel the Cessna's take-off clearance. She chose the latter, believing that an urgent cancellation would be more effective as the student pilot might panic. After both aircraft stopped, the TC instructed the Piper to vacate the runway via Taxiway W3, then allowed the Cessna to take off.
Communications and Human Factors
The radio communications between pilots, ground controller, and TC were normal. The Piper's student pilot used two radios: Radio 1 for primary communication and Radio 2 for monitoring. The cross communication occurred because both aircraft transmitted simultaneously. The student pilot's expectation of being corrected if mistaken, combined with his desire for a quick departure, contributed to the misunderstanding. The ATSM (Air Traffic Services Manual) required controllers to immediately correct any readback discrepancy; the TC's 10-second delay was noted by the investigation.
Safety Actions Taken
Following the incident, the flying school required all solo student pilots to hold one aircraft length behind the stop line at taxiway holding areas to provide extra braking distance in emergencies. The air traffic control authority reiterated the requirement for controllers to comply with the ATSM communications procedure.