What happened
On 10 November 2001, two large passenger aircraft, an A330-200 (registration AIH 065) and a B747-400 (registration AFR 3671), nearly collided in the non-radar environment of the North Atlantic Track ECHO. The incident occurred near the SOMAX reporting point at approximately 1059 UTC.
The sequence began when the pilot acting as Pilot Not Flying on AIH 065 requested westbound oceanic clearance, providing an estimated time of arrival (ETA) for SOMAX that was exactly one hour later than the actual expected time. This error was not identified by the Shanwick Oceanic Control Area (OCA) during the clearance process. Simultaneously, AFR 3671 was operating an eastbound flight at the same flight level of 370.
As AIH 065 transitioned through Shannon airspace, controllers failed to detect the discrepancy despite automated system alerts. The error only came to light when a revised estimate was communicated, revealing that the two aircraft were on a collision course. While vertical separation was eventually established, the aircraft passed within an estimated 10 NM of each other, with the pilots reporting TCAS Traffic Advisories.
The investigation
An investigation by the AAIU, in collaboration with the UK AAIB and France's BEA, examined the communications and systemic failures across several air traffic control sectors. The inquiry focused on why the initial one-hour discrepancy was missed by both the Shanwick and Shannon controllers.
Investigators looked into the procedures for oceanic clearances and the functionality of the Flight Data Processing System (FDPS). The investigation also reviewed the handover processes between different controller teams and the effectiveness of the automated alerts on the Electronic Data Display (EDD) used by Shannon controllers. Furthermore, the adequacy of the phraseology used in priority messages was scrutinized.
Findings
- The primary cause was the incorrect time estimate provided by the pilot of AIH 065, which was one hour behind the actual schedule.
- Shanwick controllers failed to perform a credibility check on the aircraft's estimate, which is a standard procedure.
- Shannon controllers did not react to a flashing alert on their EDD, which had been indicating a significant time discrepancy for at least 40 minutes.
- The clearance readback by the crew of AIH 065 did not include the time estimate, meaning neither party confirmed the erroneous data.
- The use of the word "priority" in the descent instruction was deemed insufficient to convey the extreme urgency of the situation.
- The minimum distance between the two aircraft was estimated at less than 10 NM, representing less than one minute of flying time.
Safety action
Following the investigation, several recommendations were made to prevent a recurrence, including:
- A review of ATC phraseology regarding avoiding action guidance.
- Amendments to the Memorandum of Understanding between the IAA and UK NATS to establish clearer communication protocols for non-normal situations.
- The potential implementation of a software message exchange between Shanwick and Shannon to automate the detection of flight profile errors.
- Reintroducing time estimates in oceanic clearance messages to improve verification by aircrews.