B747-400
Air Traffic Control Fully Certified
Communication Breakdown; Situational Awareness
ATC Issue All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
General None Reported / Taken
Human Factors; Procedure
I assumed the oceanic Sectors 1 and 2 in the North Pacific Ocean. Traffic volume was low and traffic complexity was low with a handful of eastbound aircraft experiencing moderate turbulence in the Central North Pacific and several aircraft coming out of Vancouver Center and on route to Anchorage Center. During the position relief briefing; the Controller being relieved relayed to me that Air Carrier X; a B744; exiting MANJO and en route to 54N140W then GRIZZ way point in Anchorage Center Sector 68 had revised coordination. Originally coming into our airspace at FL280; was revised at FL300. The Controller who took the coordination had probed the new altitude and it showed as a good altitude with no conflicts. Roughly one minute before Air Carrier X entered OC 1 and 2 at MANJO level at FL300; conflict probe activated showing Air Carrier X in conflict with Air Carrier Y; a B77W on route from ORNAI to 53N140W level at FL300. Activation of the conflict summary indicated that a loss of separation was predicted. Both aircraft were ADS/CPDLC equipped and both logged on to ADS. However; only Air Carrier Y was logged in to KZAK (Oakland oceanic log on directory) on CPDLC. Air Carrier X was already logged on CPDLC to PAZA (Anchorage Center) with his CPDLC. I sent a 'demand' to both aircraft to get a more current time and position and sent a clearance to Air Carrier Y to descend and maintain FL290 due to traffic. Once the demand came back it backed up the conflict. Air Carrier Y rejected his clearance to descend to FL290 and said he was requesting FL310. I replied that we were unable FL310 due to traffic and that he needed to descend to FL290 due to traffic. Once the clearance was sent; I sent another 'demand' to both aircraft to continue to get the most current positions and see if the 10 minutes longitudinal that the system wanted existed. The conflict summary updated again with the 'demand' and showed that the conflict was now a loss of separation. Air Carrier Y finally acknowledged the clearance to descend to FL290 and upon receipt of his level report the conflict was over. During this time; FL310 was unavailable as previously stated due to another Air Carrier at that altitude in the vicinity. If Air Carrier X had been logged in to KZAK on CPDLC as well; the D50-distance based separation flags could have been utilized and this would not have been a loss of separation situation. I had attempted several times to initiate a CPDLC connection to Air Carrier X from my end; but to no avail due to him being logged onto PAZA. I recommend that all ADS/CPDLC aircraft that will be in our airspace maintain an active log on to KZAK during their flight within the confines of our airspace. If the system is telling the aircraft to log on to the Next Data Authority; the aircraft should not log off of KZAK until clear of our airspace. This is an issue frequently with aircraft bound for Asia along B453 through from Oakland oceanic airspace into Vancouver Center and then back out into Oakland oceanic airspace. All aircraft will log off CPDCL at KANUA and many will not log back on upon reentering our airspace unless prompted by the Controller. Air Carrier X flight had logged off CPDLC from Oakland at KANUA and never logged back on at MANJO but had skipped over logging back on to Oakland and already logged on to PAZA in Anchorage while still in Vancouver Center's airspace. As stated above; if the [other aircraft] had been logged into Oakland; the distance based separation flags could have been utilized and prevented the loss of separation.
ZOA Controller described a loss of separation event while working the Oceanic Sectors when an Air Carrier failed to remain logged on via CPDLC which reportedly would have prevented this event.