What happened
On 10 November 2008, at approximately 2107 hours, two Singapore military aircraft were conducting a training sortie when the lead aircraft experienced an engine problem, characterized by unusual vibrations and sounds. The pilot declared an emergency, prompting both aircraft to abort the mission and begin a return flight to their airbase.
During this emergency descent and return, a loss of separation occurred between the trailing military aircraft and an Airbus A3/80 (registration 9V-SKA) that had departed from Singapore Changi Airport shortly before. While the military aircraft were attempting to navigate back to their base, the aircraft's flight path converged with the commercial airliner's path.
The investigation
The investigation examined the coordination between the Singapore Air Traffic Control Centre (SATCC) and Singapore Radar. It established that while the military aircraft were transitioning through the Terminal Area, the radar controller (RC) at Singapore Radar provided clearances to climb to 7,000 feet without first coordinating these changes with SATCC. Furthermore, the RC provided inaccurate altitude information to SATCC, stating the aircraft were climbing to 10,000 feet when they were actually at 9,000 feet.
Investigators also looked into the communication breakdown. The telephone system used for coordination allowed multiple controllers at SATCC to contact the RC simultaneously, leading to confusion. During the critical moments of the incident, the telephone line disconnected and reconnected multiple times, causing the SATCC Approach Coordinator to miss vital information regarding the military aircraft's intention to turn back toward the airbase.
Findings
- The primary cause of the incident was the lack of effective communication and coordination between the two air traffic control agencies.
- Non-standard radio telephony was used during telephone coordination, which prevented uniform interpretation of messages.
- Essential information regarding the aircraft's change in direction was not effectively transmitted or understood.
- The military aircraft deviated from their coordinated flight path without prior agreement with SATCC.
- The telephone infrastructure allowed multiple sources to interrupt the RC, contributing to information overload and confusion.
- There was a lack of joint training between the two agencies, resulting in a lack of shared understanding regarding operational limitations and procedures.
Safety action
Following the investigation, several measures were implemented to prevent a recurrence:
- A dedicated emergency telephone line was established between Singapore Radar and SATCC.
- Both agencies emphasized the use of standard radio telephony in daily operations.
- Singapore Radar updated its training syllabus to focus on priority of actions and standardized communication.
- The agencies initiated regular table-top exercises and expanded exchange programs to improve inter-agency coordination.