Oct. 19, 2017

Iridium is working to resolve an issue that is causing some old Data Comm messages to be delivered to aircraft after the specific clearances were no longer relevant, causing confusion among pilots.

The issue, which has affected several operators, occurred when altitude-change clearances were issued via controller pilot datalink communications (CPDLC), but not immediately delivered, to aircraft operating in oceanic airspace.

The Iridium system, which meets FAA’s specs, is set up to attempt message re-delivery for up to 24 hours. In several cases reported by operators and ATC, messages not delivered immediately were received several hours after the initial clearance was issued. In at least one instance, the aircraft acknowledged the clearance and changed altitudes, even though the instruction was for a previous flight operated nearly 24 hours earlier by the same aircraft.

CPDLC messages have time stamps that are visible to pilots. But the issue has led to at least one flight path deviation, suggesting that a change is needed to avoid old messages from being delivered when unexpected events, such as equipment malfunction, prevent pilots from getting messages right away.

Iridium is working on a temporary fix that would filter out undelivered messages that are more than 4.5 minutes old and prevent them from being delivered to the cockpit. A permanent fix will take longer, but is also in the works.

So far, en route centers in Auckland (NZZO), Anchorage (PAZA), Oakland (KZAK), New York (KZNY and KZWY), and Brazil (Atlantico SBAO) have issued NOTAMs prohibiting aircraft equipped with Iridium Satcom systems from using CPDLC. More may follow suit until the fix is in place.

The issue is believed to affect only aircraft using Iridium systems.