Sending e-mail to ATC via CPDLC

Controller pilot datalink communications are the future of international flying—and they may soon be mandatory.

Oceanic clearance is requested and delivered via ACARS. All entries must be checked before pressing SEND.

Rockwell Collins says that data­ink communications applications for automatic dependent surveillance contract (ADS-C) and CPDLC will be available beginning in the 2011 time frame. For existing aircraft, an FMS upgrade—which is presently under development—will permit incorporation of ADS-C and CPDLC.

Crew procedures

While ATC communications via CPDLC text messaging are fairly easy to learn and to handle, they should be approached in a systematic way to ensure that all clearances are understood completely and correctly by both crewmembers.

To illustrate, let us join an imaginary crew as they make their way up the coast of Nova Scotia on a beautiful evening. The cockpit instrument panel glows red as the sun settles in the west, the purple shadow of night approaches from the east, and the lights of Halifax are clearly visible down below.

Preparations for the ocean crossing on the flight to Europe are well under way. We start with the oceanic clearance, since our assigned route might be different then filed. Instead of voice communications with the required readback, we request the clearance via ACARS. Between 90 and 60 min before the oceanic entry point, the clearance request should be sent to Gander.

The screen prompts require us to enter the ETA for the oceanic entry point, as well as the flight level and Mach number requested for the crossing. There is a additional free text line on the oceanic clearance request screen—many crews use this to tell ATC the maximum flight level they can accept. Both pilots review the request before it is sent out, including the correct flight or tail number.

And we are sure to use the correct entry point, since the system will not accept any other waypoint. After pressing SEND, the crew receives a printer message from Gander indicating receipt of our request as well as the instruction to contact Gander via voice if no clearance is received within 15 min of oceanic entry point.

The oceanic clearance itself may take quite a while, since Gander ATC is busy feeding all traffic from North America into the North Atlantic bottleneck so as to arrange for the larger longitudinal and lateral separations required over open water. However, after a while, we receive the oceanic clearance on the printer.

It is a complete route clearance for the oceanic portion of our flight and lists all lat/long coordinates of our waypoints. Mach number and flight level are also part of the clearance. We review the clearance and press ACCEPT. This generates a 3rd telex with the important message CLEARANCE CONFIRMED. The flightcrew keeps these 3 telexes, and uses them to crosscheck the FMS routing to ensure that everything is correct.

Gander and Shanwick do not react kindly to navigation errors on the North Atlantic. All true tracks and distances on the flight log should be checked against the FMS, but that has been procedure for many years and is not related to CPDLC. As we approach the oceanic entry point, it is time to log on to Gander Oceanic via CPDLC.

On the ATC page of our FMS CDU we select the LOGON/STATUS prompt and again make sure that the flight and tail number are correct. We have to enter the 4-letter code of the ATC center—in this case CZQX for Gander Oceanic. After a minute or two, our logon is accepted and the active center shown as CZQX. The message ATC COM ESTABLISHED is displayed on the FMC CDU.

In North Atlantic airspace, ADS is an integral part of CPDLC—therefore, our FMC ATC screen also shows ADS active. This means that position reports are transmitted automatically via satellite to Gander and Shanwick control centers.

The position reports are then used to calculate and display a virtual radar image on the controller’s screens. Now the only thing that remains to be done is a SelCal check on HF. HF serves as a backup for CPDLC. The crew calls Gander Radio on HF and tells them that CPDLC is established, the next ATC unit (Shanwick) and our SelCal code.

Gander res­ponds by sending the SelCal tone, and informs us that voice position reports are not required. The next voice frequency—in this case the HF frequency for Shan­wick—is also given to the crew. After all this work it now becomes nice and quiet on the flightdeck. It’s time to sip a coffee and enjoy the northern lights in the night sky.

There is no need for communication with ATC until 30° W. At this point the CPDLC system transfers automatically to Shanwick. The LOGON/STATUS page indicates the transfer, and the only item that remains to be done is to check in with Shanwick via HF voice for a SelCal check.

As we approach landfall in Ire­land, Shanwick sends us a CPDLC message with instructions to contact Shannon on a VHF frequency. Shortly thereafter, the FMS message ATC COM TERMINATED tells us that it is time to join the regular ATC world again, and the usual VHF radio chatter stays with us for the remainder of the flight.

A need for care

The oceanic clearance printout serves to crosscheck FMS route entries and the master flightlog. It is important to watch for amended clearances.

The introduction of CPDLC on the flightdeck has obvious benefits in ATC communications. However, it is not without pitfalls—for example, clearances may be lost or misunderstood. It is important to work in a structured manner with all communications via CPDLC.

All CPDLC messages should be read aloud by the pilot not flying, for example with this wording: ”ATC message page 1 of 2—Contact Shannon on 130.75.” The response, eg, WILCO in this case, should be sent promptly. Only after the response has been sent will the status of an ATC message change from OPEN to COMPLETE.

Clearances, such as route clearances or climb/descent instructions, should also be printed. After each flight, the entire ATC log should be printed and filed with the other flight documents. As you might expect with an international program, while all CPDLC procedures appear to be similar, there are significant regional differences.

The best program by far is the North Atlantic region, where the combination of ACARS clearance request and delivery, CPDLC communication and ADS position reporting makes full use of the available technology.



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