A B747-400 flight crew became confused over the designators of ZAK and ZOA and what each represents.

Narrative

Rewritten in plain English from NASA’s original all-caps telegraphic report — facts, figures, and terminology preserved.

Attached is a description of the event/s events as recorded in flight just after it occurred. For clarification, 'howgozit' of our flight (item #1) is included. A NOTAM is item #2, and communications are items #3 through #5. The communications difficulties that our flight encountered were not so unusual for this location, and reception problems were resolved as the flight progressed eastbound. However, I believe that the NOTAM which tries to provide guidance to pilots for communication procedures is confusing. It refers to aircraft exiting ZOA FIR. What's that?

We were logged onto ZAK and, according to every chart we could find, talking to Oakland. We were logged on to ZAK using CPDLC. We were not logged on to ZOA, and no member of the crew was aware of such an ident for Oakland. While navigating in class 2 airspace, aircraft X was communicating via CPDLC and was logged on to ZAK for ZOA. Estimate for pretty was YY16Z. FIR estimate was YY32Z. At +YY29Z, a message was received from 'ATC uplink' to contact CZVR CTR on 133.4 MHz. A response was sent at YY30Z. Several calls were made on 133.4 to establish contact and give progress with no response. A position report was made in the blind.

About this time, a CPDLC message (ATC message) appeared something like 'ATC COM log-off' from Oakland (ZAK). During this time, an HF SELCAL from SFO commercial radio came in, and we were unable to establish voice contact due to poor HF communications quality. After switching to the secondary frequency, we received a voice call (weak and barely readable) to contact Vancouver on 135.2. We did so and upon call-up the controller said 'radar contact; no position reports required.'

About this time, or just after, an ACARS message was received at YY38Z 'ZOA requests aircraft X contact CZVR CTR 135.2.' But in the meantime, Vancouver had switched us to another frequency. We then called Vancouver CTR to inquire as to the need for a change to 135.2 and they told us to disregard. At YY47Z, another ACARS message was received (and accepted) indicating that per NOTAM, we were required to contact commercial radio prior to exiting at ZOA FIR. The NOTAM indicates datalink users are to contact commercial radio for VHF/HF frequency in next sector prior to exiting ZOA FIR and gives several frequencies, including 135.2. Aircraft plotting chart indicates FIR as 'Oakland Oceanic ZAK FIR' as does commercial chart Pacific Ocean and Canada-Alaska high altitude enroute chart.

We called ZSE to confirm the nomenclature of Oakland FIR. They indicated it is ZOA and Anchorage is ZAK. Conflicting, or at least apparently confusing, verbiage along with an assignment of a frequency by the CPDLC and past experience of poor VHF communication approaching Vancouver allowed the crew to believe they were communicating as ATC had directed. This is exacerbated by the relatively new use of CPDLC on an easterly routing in this area and the lack of responses to position reports from ATC when using this method.

Callback conversation with reporter revealed the following info: reporter participated in FANS structured callback program. Reporter had never heard of ZOA or even knew where the ZOA ADIZ was located. He only knew ZOA designation as ZAK. When the ZSE controller said ZAK was Anchorage CTR, then the pilot was confused. They were able to make radio contact, but not when they expected to. This is what caused them to ask questions of the controllers. It was never clear until analyst explained the designators in easy to understand terms.