A United Airlines Boeing 777-200 enroute from London Heathrow to Houston TX, narrowly avoided a potential conflict with a FedEx Boeing 777-200 freighter outbound from Memphis TN, to Paris.
The incident occurred approximately 160 nautical miles east-northeast of Gander, Newfoundland, Canada on 21 June 2025. It highlights the critical role of air traffic control (ATC) and onboard safety systems.
Loss of Separation Incident over Atlantic
United Airlines flight UA879 was cruising at flight level 340 when the crew requested a climb to FL360. Oceanic Control instructed them to stand by.
Meanwhile, FedEx flight FX10 was enroute to Paris at FL350 in the opposite direction. Due to an error, Oceanic Control issued a Controller-Pilot Data Link Communication (CPDLC) clearance to United UA87.
It directed the flight to proceed to the TOPPS waypoint and mistakenly authorized a climb to FL360.
The controller quickly recognized the error and issued a voice instruction to flight UA879 to maintain FL340 and disregard the CPDLC clearance.
Despite this, UA879 began climbing and reached FL345 (34,500 feet). ATC then reiterated the instruction to descend to FL340.
The United crew reported a Traffic Collision Avoidance System (TCAS) advisory, which likely alerted them to the nearby FedEx aircraft. They descended to FL340, restoring the standard 1,000-foot vertical separation within seconds.
Outcome and Safety Response
According to the Canadian Transportation Safety Board (TSB), both aircraft safely continued to their destinations without further issues.
The swift response from ATC and the United UA879 crew, combined with the TCAS advisory, ensured no undue loss of separation or collision risk. The incident underscores the importance of clear communication and robust safety systems in aviation.
This event highlights the complexity of oceanic air traffic management, where aircraft operate beyond radar coverage and rely on precise ATC instructions.
Errors in CPDLC, a text-based communication system, can occur, but voice instructions and TCAS provide critical backups. The TSB’s report emphasizes the effectiveness of these systems in maintaining safety.
Aircraft Details
The aircraft operating United Airlines flight UA879 was a Boeing 777-200, registered N78002. This is a 26.8 year old widebody aircraft belonging to the carrier United Airlines. It has been operational service with the airline since October 2010.
The freighter aircraft operating FedEx flight FX10 was a Boeing 777F, registered N879FD. This is a 6.7 year old converted freighter aircraft belonging to the carrier FedEx Express. It has been in operational service with the operator since October 2018.