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On 16 June 2004, a Boeing 747-400, registered GC-IVC (IVC), was en-route from Melbourne to Singapore on airway A576. The aircraft was approaching the boundary between the Brisbane flight information region (FIR) and the Bali FIR at flight level (FL) 340. Concurrently, a second 747, registered 9V-SPE (SPE), was en-route from Sydney to Singapore on airway G326. That aircraft was also approaching the boundary between the Brisbane FIR and the Bali FIR at FL 340.

The controller recognised that he had to resolve a potential confliction between SPE and a third aircraft. In resolving that confliction, the controller created a new confliction between IVC and SPE. In response, the controller instructed the crew of IVC to reach FL320 by waypoint ATMAP (see Annex A). That requirement was intended to achieve vertical separation between the aircraft prior to any loss of lateral separation1. However, the required lateral separation point was 94 NM south-east of waypoint ATMAP on airway A576. The incorrect requirement led to an infringement of separation standards.

Following a scan of the air situation display, the controller realised that he had issued an incorrect requirement. The controller then issued a second requirement, via the high frequency (HF) radio operator, for IVC to descend to reach FL320 by 80 NM to the south-east of waypoint ATMAP. The controller reported that this requirement was based on the application of a required navigation performance (RNP) 10 separation standard2. This standard was not authorised for use within the Bali FIR. Upon issuing the requirement, the controller handed over to another controller and went on a scheduled break.

Over a period of 10 minutes and 37 seconds, the HF radio operator made 12 unsuccessful attempts to contact the crew of IVC. The oncoming controller realised that the HF radio operator had not been able to make contact with the crew of IVC. He also realised that RNP 10 was not an authorised standard. By that time the authorised separation standards had already been infringed. The oncoming controller then successfully instructed the crew of IVC to descend their aircraft immediately to FL320 , via a controller pilot data link communication3 (CPDLC) message to the crew of another aircraft.

The controller involved in this occurrence had completed his field training in April 2004. A review of his training records indicated that he had approximately five weeks' experience on that sector of airspace. According to his check and standardisation supervisor, the controller demonstrated a satisfactory level of competency on completion of his sector-specific training.

The controller was rostered to work an afternoon shift, which commenced at approximately 1500 eastern standard time. During the shift the controller had a break of one hour, returning to the console at approximately 1930. The incident occurred at 2038. There was no evidence that fatigue played a part in the incident.

Coordination of high frequency radio communications

The controller issued the requirement to the crew of IVC to reach FL320 by waypoint ATMAP while that aircraft was within reliable very high frequency (VHF) radio range. However, when the controller realised the error in the requirement, that aircraft had passed outside VHF radio range. The controller attempted to issue the amended requirement to the crew of IVC through a HF radio operator, because the crew of IVC had not nominated CPDLC on their flight plan as a means of communication with ATC.

The HF radio operator was unable to establish two-way communication with the crew of IVC, to pass the amended requirement, despite repeated attempts. The controller was not aware that the HF radio operator was unable to issue the instruction to the crew of IVC.

The controller did not confirm with the HF radio operator that the instruction had been passed to the crew of IVC, and there was no published procedure requiring him to do so. Although there was a requirement for the HF radio operator to notify the controller that the instruction was not passed to the crew of IVC, there was no formal procedure to facilitate that notification.

1 Lateral separation is considered to exist when there is at least a 1 NM buffer between the possible positions of two aircraft (ICAO PANS-ATM, Chapter 5 in CASA Manual of Standards Part 172
2 For RNP10, the approval process must show that the total navigation system error in each dimension must not exceed +/- 10 NM for 95 per cent of the flight time on any portion of any single flight:
a) the true position of the aircraft must be within 10 NM of the programmed route centre line; and
b) the true distance to way-points must be within 10 NM of the displayed distance to waypoints.' (International Civil Aviation Organization, 1999, Manual on required navigation performance [RNP], second edition, p. 6).

3 Controller Pilot Data Link Communications (CPDLC): A means of communications between a controller and pilot using text-based messages via an ATC data link (Manual of Air Traffic Services, part 10, effective 10 June 2004).

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