CPDLC downlinks

[Jagohu]

Hi all!

I'd like to ask from the pilots flying around with a/c equipped with CPDLC about the messages they can downlink to us...
Today I've had a Speedbird - and if I understood well - they tried to downlink us a message that they're picking up an ELT signal... We've received the message, but our system couldn't understand it and the only thing we saw in the CPDLC window was something like "invalid msg".
I'm just wondering if I got it right and actually there's a possibility to downlink stuffs like that - and if so, what other messages can you downlink besides the "standard" (level, dct)...
Thanks a lot in advance!

[rab-k]

CPDLC in Oceanic airspace works by utilising a series of pre-formatted messages, (with associated replies), together with the ability to send 'Free-Text' messages. The North Atlantic (NAT) Region currently utilises Phase 3 CPDLC Message Sets, however Phase 4, (full functionality), is due to commence later this year.

ATC systems will only deal with the message sets which they are technically, (or otherwise), able to process. The system here at Shanwick, for example, will identify Phase 4 message sets not currently accepted and create a "Message Not Supported By This Facility" reply.

The aircraft may be able to downlink a host of message formats and free-text messages, but if the receiving system is not able to accept these then the error messages will appear, e.g. "Invalid Message". The "Free-Text" facility here at Shanwick would enable you to receive any non-standard message, including information of a suspected ELT signal.

CPDLC has been used in Oceanic Airspace for several years and a search of ICAO documents on-line will turn up a host of related papers. Like I say, hopefully the Phase 4 Message Sets will be functioning later this year in the NAT Region.

What we in ATC are able to do with CPDLC is governed more by the capability of the ATC system with which we operate than the capability of the aircraft with which we communicate.