Shanwick Bogus Messages

By Declan Selleck


Just around New Years, a story started growing legs about Bogus CPDLC messages from Shanwick and Gander. In the most worrying version of events, the G550 crew received a “Descend at Max Rate” type message on CPDLC, and when they checked on voice with ATC it hadn’t come from them.

We had lots of replies on this – both by email and in slack, thanks everyone! So here is the event summary as pieced together by the community:

– This was a single event that happened in December, at 0500Z one morning, to a G550
– It was caused by an avionics bug in the FMS – a valid error message was parsed incorrectly and assigned a value of “Descend at max rate” by the FMS, which appeared on the screen.
– Fears of it being some kind of spoofing or hack are unfounded. The initial story spread like wildfire! But ultimately, a non-event.

Confirm Assigned Route

This was the second part of the concerns about CPDLC messages from Shanwick. Lots of crews have been getting an FMS message after passing the Oceanic Entry Point saying “Confirm Assigned Route”. We’ve probably gotten 50 distinct messages/emails/queries on this. Many crews don’t know quite what this is or what to do with it, and many wondered if it was also a “bogus message”.

This is normal. It’s a new procedure, and this message is now automatically sent by Gander, Shanwick, and Iceland. The reason for the message, is to act as a cross check, now that we’re all cruising with 30 miles between us instead of the old school 60. When you do “Confirm Assigned Route”, then ATC knows that you’re both on the same page.

We first mentioned it here in November, have a read. The only recent update is that Gander and Iceland have automated the CPDLC message, so everyone that logs on will get the “Confirm Assigned Route” message.


More on the topic:

More reading:

Declan Selleck

Declan Selleck

Declan is a Flight Service Specialist with OPSGROUP.


  • Hey Chad – thanks for the additional background information, and for posting it here – that’s helpful. Great to see detailed analysis of the incident.

  • Below is a verbatim response directly from Honeywell (manufacturer of the G550’s avionics) per my inquiry into this incident:

    During our analysis of the reported incident, we found that blog had some incorrect information because it was not an uplinked error message but rather a downlinked error message. We have never seen and have not received other reports of this issue. We are currently still investigating the root cause but believe this is an isolated incident that will not affect other systems. A technical explanation of the findings to date are below.

    The blog was incorrect to state that Shandwick had uplinked a bogus message to a Gulfstream G550 equipped with a Honeywell FMS. As can be seen in the photos from the blog, “↓ DESCEND AT * MAXIMUM” is actually a downlink message to ATC (note the downward facing arrow) from the FMS, not an uplink from ATC.

    Additionally, the next message, “↑ DOWNLINK ERROR” is an uplink from ATC that was sent indicating there was something incorrect with that specific downlink. This uplink from ATC, which indicated that ATC has rejected the downlink, demonstrates the end to end communication protocol is working per design.

    Honeywell reviewed the message logs obtained from the service provider and confirmed that at the same time the “↓ DESCEND AT * MAXIMUM” message was displayed on the ATC LOG page, a downlink was observed in the logs, but the data was corrupt (unable to decode into any expected data format). Downlink messages are generated by the FMS and stored in the ATC LOG. This one downlink was erroneously encoded by the FMS as corrupt data, and the ATC LOG page display decoded the corrupt data as “↓ DESCEND AT * MAXIMUM”. The presence of the star in the message indicates the FMS decoded to the “↓ DESCEND AT * MAXIMUM” message but could not decode a valid vertical rate (for example, should display as DESCEND AT 1000 FT/MIN MAXIMUM) so displayed a star instead.

    Honeywell is still determining the root cause but we can confirm that message was generated by the FMS and that this was not the result of, “spoofing or hack.”

  • Declan says:

    Yep, it sure was – all authorities were of course concerned. Fully investigated, and the reason for the error was found – a software bug.

  • Good morning.
    May I know if the “incident” of G550 bogus message, was followed by an official investigation ?


  • Jose Guillermo Barillas says:

    Well done, thanks.

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