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On 28 November 2004, a Boeing Company 747-438 aircraft was en route from Sydney to Singapore at flight level (FL) 360. Another Boeing Company 747-400 aircraft was en route from Bangkok to Sydney at FL350. At 1509, the crew of the 747-438 had been issued with a clearance to climb to FL380 with a requirement to reach that level by 1550 and the crew planned to leave FL360 at 1544. At 1521, the crew of the 747-400 requested a clearance to climb to FL370 and were issued a clearance to reach FL370 by 1528. This resulted in an infringement of separation standards.

At 1538, approximately 150 NM north-west of waypoint NIKOM, the crew of the 747-438 observed an aircraft pass overhead. They informed the controller, and confirmed that they had a clearance to climb to F380. The controller acknowledged the crew, but took no further action to resolve the infringement of separation standards.

The controller reported that when he issued the climb instruction to the crew of the 747-400, his mental picture was that the 747-438 was maintaining FL360, and this was reinforced by a simultaneous separation problem with another aircraft. He also reported that it was possible that he may also have mixed up the displayed levels for the 747-438.

The controller indicated that his sleep pattern had been disrupted, and while he had assessed himself as fit for duty, and felt competent to acquit the required task, he felt ‘a bit more fatigued than normal’.



While it was not possible to determine the controller’s level of fatigue, it is likely that the significant level of workload and the controller’s acknowledged diminished level of mental alertness and the time of day, together contributed to the incident.

The routine display of CLAM alerts for expected events, such as the issue of discretionary climb, did little to enhance the controller’s situational awareness in regard to QF31s cleared level status.


Safety Action

As a result of this occurrence, Airservices Australia has advised the Australian Transport Safety Bureau that it is reviewing the following issues in order to strengthen the operational risk controls for prevention and recovery from, similar occurrences:

  • The Australian Advanced Air Traffic System’s (TAAATS) existing human machine interface for effectiveness and efficiency and to ensure standardisation
  • Airspace, for division both laterally and vertically, to reduce airspace complexity and facilitate an improved ASD
  • Route structure, to remove unnecessary waypoints to assist controller interaction with data input
  • Coordination requirements, both domestically and internationally, to reduce complexity and controller workload, through increased automation
  • Supervision available, by either increasing the hours of operation of operations supervisors to 24 hour coverage, together with additional training, or by the provision of additional training for systems supervisors, for night time operation
  • The location of workstation positions at night, for improved peer support and situational awareness
  • Refresher training, to ensure all staff have completed required training in active listening, scanning, separation assurance, and recovery from an unusual situation such as a breakdown of separation. Additionally ensuring that this training adequately covers compromised separation in the non-radar environment.

In addition, The TAAATS Alerts Review and Enhancement Project is currently reviewing the processing and display of CLAM and other alerts for controllers. Software is currently being developed to allow a flight plan conflict function display for procedural tracks, including ADS tracks, for delivery late in 2006.

General details
Date: 28 November 2004 Investigation status: Completed 
Time: 1528 UTC  
Location   (show map):278 km NW NIKOM, (IFR) Investigation type: Occurrence Investigation 
State: International Occurrence type: Loss of separation 
Release date: 14 November 2005 Occurrence class: Airspace 
Report status: Final Occurrence category: Incident 
 Highest injury level: None 
Aircraft 1 details
Aircraft manufacturer: The Boeing Company 
Aircraft model: 747 
Aircraft registration: HS-TGJ 
Serial number: NA 
Type of operation: Air Transport High Capacity 
Damage to aircraft: Nil 
Departure point:Bangkok Thailand
Departure time:0815 UTC
Destination:Sydney NSW
Aircraft 2 details
Aircraft manufacturer: The Boeing Company 
Aircraft model: 747 
Aircraft registration: VH-OJM 
Serial number: 25245 
Type of operation: Air Transport High Capacity 
Damage to aircraft: Nil 
Departure point:Sydney NSW
Departure time:0815 UTC
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Last update 13 May 2014