Incident Overview
On 10 November 2008 at about 2107 hours, two Singapore military aircraft (designated A/C 1 and A/C 2) were on a training sortie when A/C 1 declared an emergency due to an engine problem. The sortie was abandoned, and the aircraft returned to their airbase. During the return, A/C 2 became involved in a loss of separation incident with an Airbus A380 (registration 9V-SKA) that had departed from Singapore Changi Airport minutes earlier. No injuries or damage were reported.
Sequence of Events
A/C 1 and A/C 2 had taken off from a Singapore airbase at about 2100 hours under the control of the airbase tower. After departure, they flew eastward and entered the Terminal Area (TMA) controlled by the Singapore Air Traffic Control Centre (SATCC). The airbase tower transferred control to SATCC Approach Control, which cleared the two aircraft to climb to 4,000 ft. During the climb, the pilot of A/C 1 heard an unusual sound and felt vibration. He continued climbing while troubleshooting.
Meanwhile, the Airbus A380 (A/C 3) took off from Runway 02L of Changi Airport and contacted SATCC Approach at 600 ft. The Approach Controller cleared A/C 3 to climb to 7,000 ft on a heading of 110°.
At about 2107 hours, after A/C 1 and A/C 2 reached 4,000 ft, SATCC Approach transferred control to the military radar controller (RC) in Singapore Radar. Shortly after, the pilot of A/C 1 declared an emergency to the RC. The RC inquired about assistance, and the pilot requested a climb to 10,000 ft. Aware of another aircraft at 8,000 ft to the east, the RC cleared A/C 1 and A/C 2 to 7,000 ft without coordinating with SATCC.
The SATCC Arrival Controller then called the RC to coordinate an arrival. The RC informed the Arrival Controller of the emergency and that A/C 1 and A/C 2 were cleared to 7,000 ft and proceeding to waypoint HOSBA. The nature of the emergency (engine trouble on a single-engined aircraft) was not conveyed. The RC advised the Arrival Controller to keep A/C 3 clear.
Air Traffic Coordination
The SATCC Approach Controller, aware that A/C 3 was heading toward HOSBA, instructed A/C 3 to turn to heading 170° and climb to 8,000 ft to provide separation. The Singapore Radar Supervisor, monitoring the emergency, stepped in to assist the RC. He cleared A/C 1 and A/C 2 to climb to 9,000 ft after consulting the RC.
Subsequent coordination between Singapore Radar and SATCC involved misunderstandings. The RC informed SATCC that A/C 1 and A/C 2 were climbing to 10,000 ft (instead of 9,000 ft) to reserve airspace. SATCC Approach maintained A/C 3 on its heading and altitude based on that information.
A/C 1 and A/C 2 then turned right to return to their airbase. The SATCC Approach Coordinator observed the turn and queried the RC. The telephone line disconnected and was re-established. The RC confirmed the aircraft were returning.
Findings
The investigation identified the following:
- The pilot of A/C 1 correctly declared an emergency.
- Singapore Radar personnel did not fully pass essential information to SATCC, including the nature of the emergency.
- The RC did not coordinate the first climb clearance to 7,000 ft with SATCC as required by standard operating procedures.
- Communication was not well managed; calls from SATCC were not always answered by the designated coordinator.
- The climb clearance to 9,000 ft was given without prior coordination with SATCC.
- Incorrect altitude information (10,000 ft instead of 9,000 ft) was passed to SATCC.
- The actions of SATCC controllers were appropriate based on the information available to them.
Safety Actions
During the investigation, the following safety actions were taken:
- The Singapore Armed Forces (SAF) reviewed standard operating procedures for coordinating emergency recovery of military aircraft through the Changi TMA.
- The SAF revised the training curriculum for military radar controllers to include specific training on coordination with SATCC during emergencies.
- The Civil Aviation Authority of Singapore (CAAS) and SAF jointly developed a new coordination telephone line dedicated for emergencies only.
- The CAAS reviewed and revised the operational letters of agreement between SATCC and Singapore Radar.
Safety Recommendation
The Air Accident Investigation Bureau of Singapore recommended that the CAAS and SAF review procedures for the transfer of control of military aircraft between SATCC and Singapore Radar during emergencies to ensure timely and efficient transfer.