Loss of separation between a Boeing Co 747-400, 9V-SPE and a Boeing 747-400, GC-IVC, 16 June 2004

Communications

The reason the HF operator was unable to establish two-way
communication with the crew of IVC could not be determined. A
formal procedure for notifying the controller that the HF radio
operator could not pass the instruction to the crew of IVC may not
have ensured that a separation standard existed, as an incorrect
instruction had been issued. However, it may have prompted a more
timely reassessment of the situation by the controller. In other
circumstances, a formal procedure may alert the controller in
sufficient time for action to be taken before separation standards
are infringed.

Air Traffic Controller

A review of the controller's training records indicated that he
had an adequate understanding of the concept of lateral separation.
However, his misapplication of a lateral separation point may have
reflected his lack of proficiency due to inexperience in working
the particular sector of airspace.

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
10.8.1.1).

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).