Message delivery glitch hits Iridium CPDLC

Controller Pilot Data Link Communications via the Iridium Satcom network have been suspended after US aviation authorities issued a temporary ban within the New York / Oakland / Anchorage Flight Information Region (FIR).

The Iridium system 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, an 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.

The issue has led to at least one flight path deviation, suggesting 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.

The United States Federal Aviation Administration (FAA) issued NOTAM # A0622 / 17, prohibiting the use of CPDLC communications via Iridium in the FIR Oakland and Anchorage on October 10 following a transmission / reception failure of a critical message sent via CPDLC in which an aircraft received a flight level change instruction only after landing.

A0622 / 17 – FOR ACFT EQUIPPED WITH IRIDIUM SATCOM, USE OF CPDLC IS PROHIBITED WI THE ANCHORAGE OCEANIC, DOMESTIC AND ARCTIC FLIGHT INFORMATION REGIONS. FLIGHT CREWS CAN LOGON TO PAZN OR PAZA, AS APPROPRIATE, TO ALLOW THE USE OF ADS-C FOR POSITION REPORTING. COMMUNICATION WITH ANCHORAGE ARTCC MUST BE VIA HF; CPDLC IS NOT AUTHORIZED. IF USING ADS-C POSTION REPORTING, HF VOICE POSITION REPORTS ARE NOT REQUIRED UNLESS SPECIFICALLY REQUESTED. SFC – UNL, 10 OCT 22:30 2017 UNTIL 10 NOV 22:31 2017 ESTIMATED. CREATED: 10 OCT 21:44 2017

The ban was extended to New York FIR according to NOTAM A0502 / 17:

ZWY A0502 / 17 International 10/13/2017 1927 12/30/2017 0800 USE OF CPDLC AND ADS-C VIA IRIDIUM SATCOM IS PROHIBITED WITHIN NEW YORK CENTER OCEANIC AIRSPACE

A spokesman for Iridium tells Air Traffic Management there there were two ‘odd’ circumstances that had nothing to do with whether or not the Iridium system was working as expected and as approved – one related to the communications management unit (CMU), one procedural.

“The system has been and is working as it always has. This was not a bug or problem with our network. It was a unique scenario discovered in practice, so the FAA asked us to modify how our system works, and we are quickly complying,” he said.

In one instance, the pilot used Iridium when he was meant to be using Inmarsat as part of Swift Broadband FAA trials. “The pilot later realised this in-flight and turned off Iridium CPDLC, but did not ‘log off’ formally before transitioning to using Inmarsat,” the spokesman said. “Messages from the communications service provider kept trying to reach the aircraft using Iridium for a period of time but were never delivered, so they remained in queue as per requirements.

“Approximately 23 hours later, the aircraft switched back to Iridium and the old messages were delivered. Despite the timestamps indicating the age of the messages and that the flight ID for the message was for an earlier flight, the messages were accepted by systems on board the aircraft,” he continued, adding, “You can ask why they accepted and presented those messages, but that’s not our focus and we understand whatever the reason for it, onboard avionics take a long time to fix, test and change on multiple aircraft.”

In the other instance, he explained, the aircraft CMU crashed and did not have the latest software which automatically filters out ‘old’ messages based on the time stamp. Once reset, the cache was not cleared and then, similarly, the queued messages were delivered.

“Upon discovery of these instances, Iridium immediately began implementation of a solution that will prevent CPDLC messages four minutes old per FAA instruction,” said Iridium.

“Iridium has successfully regression-tested and implemented the enhancement to our messaging platform at the heart of the FAA NOTAM. This enhancement deletes aviation messages in the queue which have not been delivered within four minutes from entering Iridium’s message queue. The messages are still maintained/managed within our replication database if required by the ANSP. Third party tests with ARINC, SITA and a few of the aircraft OEMs to validate that our enhancement meets the revised FAA request are underway.”

He said it was important to note that while Iridium’s messaging platform that supports CPDLC operated in compliance with FAA requirements, Iridium is responding to the NOTAM by enhancing its system to quickly meet the new FAA request with a tested solution that shall be validated by industry third parties in order to return to Iridium CPDLC service in all FAA airspace.”

So far, en route centres 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.

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