A Boeing 747-48HE registered VH-OEB (OEB) was en-route from Los
Angeles, USA to Auckland, New Zealand was maintaining flight level
(FL) 330 as assigned by Tahiti air traffic control (ATC). A Boeing
747-4H6 registered VH-OED (OED) was en route from Auckland to Los
Angeles and was also maintaining FL330. The crew of OEB reported
that they observed, on their traffic alert and collision avoidance
system (TCAS), another aircraft that was on a reciprocal track at
the same level (OED). The crew of OEB turned their aircraft right
15 degrees and descended to FL325. The crew of OED later reported
that they observed, on their TCAS, another aircraft that was on a
reciprocal track at the same level (OEB), and climbed their
aircraft to FL333. A third aircraft, a Boeing 747, was en-route
from Los Angeles to Auckland at FL340. The crew of OED also
observed an indication of that aircraft on their TCAS.
The vertical separation standard was 1,000 ft. The vertical
distance between OED and OEB reduced to 800 ft, and to 700 ft
between OED and the third aircraft. There was an infringement of
separation standards.
The crews of OEB and OED were communicating with Tahiti ATC via
both Controller-Pilot Data Link Communications (CPDLC) and high
frequency (HF) radio. CPDLC was a 'means of communications between
a controller and pilot using data link for [Air Traffic Control]
communication' (ICAO Doc 4444 ATM/501 14.1.1). Messages were
compiled and initiated either by the crew of the aircraft or by ATC
and were, in this case, pre-formatted. The use of pre-formatted
messages was 'intended to reduce the possibility of
misinterpretation and ambiguity' (ICAO Doc 4444 ATM/501
14.3.4).
The crew of OEB had requested climb from FL320 to FL340 but that
request was denied. About ten minutes later the crew of OED
requested climb from FL330 to FL350. Tahiti ATC asked the crew of
OED, via CPDLC, when they could reach FL350 and then denied the
request for climb. The French Bureau d'Enquetes et d' Analyses pour
la Securite de l'Aviation Civile (BEA) produced a report on the
occurrence. The BEA reported that the crew of OED then contacted
Tahiti ATC via HF radio and advised that they could reach FL350 by
time 1140 universal coordinated time. The controller responded via
HF radio and instructed the crew of OED to maintain FL330. The crew
of OEB then requested, via CPDLC, climb to FL330. The CPDLC
response provided to the crew of OEB was 'climb to and maintain
FL330 due to traffic' even though FL330 was not available. The
message was selected by the controller from the menu of
pre-formatted messages available in the system.
The South Pacific Operations Manual (SPOM Part 5.5) stated that
'when a clearance request is denied, the controller shall use the
element "UNABLE" in the uplink message'. The SPOM detailed the
procedures and requirements applicable in the South Pacific flight
information regions (FIRs) for CPDLC equipped aircraft and applied
within the Tahiti FIR. The SPOM (Part 5.1) also stated that
`generally, when a CPDLC aircraft is operating within a CPDLC FIR,
CPDLC will be the primary means of communication'.
Subsequent to the occurrence OEB returned to FL320 and OED
returned to FL330. The crews then reported to Tahiti ATC at those
respective levels. The controller had not intended to assign FL330
to the crew of OEB and did not realise that they had been assigned
FL330, or that they had climbed to FL330 and subsequently returned
to FL320. When the crews reported at FL330 and FL320 respectively,
after the occurrence, that information was consistent with the
information the controller had recorded on the flight progress
strips. The controller was not aware that there had been an
infringement of separation standards.
The BEA reported that the controller believed there were
possibly two reasons why a climb instruction had unintentionally
been assigned to the crew of OEB:
1. In reply to the request by OEB for climb to FL330, the
controller pre-selected the wrong pre-formatted CPDLC message and
sent the message without checking it, or
2. The controller confused the two aircraft because of their
similar callsigns.
The BEA reported that four controllers had been rostered for the
period between 1900 hours and 0700 hours (Papeete local time) and
were rostered to cover the aerodrome control position, the approach
control position and the area control position. The event occurred
at 0050 Papeete local time. The controller involved in the
occurrence was alone in the tower at the time of the occurrence and
was performing all three functions. That controller considered that
the workload was high due to poor quality HF radio, increased
coordination with other centres in relation to aircraft using
'flexible routes' and difficulty validating CPDLC messages with
OED.
The controllers at Tahiti had been trained in France but that
training had not included the use of CPDLC. Initial training on the
use of CPDLC was incorporated into a one-week training program in
Papeete that included CPDLC with other local training requirements.
Ongoing CPDLC training was incorporated into on-the-job training
which could take controllers around 57 weeks to complete.
Controllers reported that the initial training was essential but
they had not been exposed to the system sufficiently during
training to master all aspects of the system.
The controller involved in the occurrence had been working
Tahiti Oceanic Controlled Airspace for approximately three and a
half years and was qualified on the three ATC positions being
managed at the time of the occurrence.
