The Federal Aviation Administration says it is investigating an incident involving three aircraft that were circling over North Texas during severe weather this past week.
The FAA described the incident in a statement Wednesday as a "loss of standard separation" that occurred while two cargo jets and a passenger plane were in holding patterns near the Dallas-Fort Worth area Thursday evening. At the time, flights coming into North Texas airports were delayed or kept away as severe storms pushed through the region.
The FAA said preliminary information shows that the pilots of FedEx Flight 3952, a Boeing 767, responded to an automated alert from an onboard Traffic Collision Avoidance System due to the indicated proximity of UPS Flight 5510, a Boeing 747.
While responding to the alert, the FedEx flight descended into a 1,000-foot vertical safety buffer between it and United Airlines Flight 2319, a Boeing 737. The crew of the United Flight then descended in response to their own alert, the FAA said.
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According to a preliminary analysis of the event, the closest proximity between the FedEx 3952 and UPS 5510 was 1.1 miles laterally and 900 feet vertically. The closest proximity between FedEx 3952 and United 2319 was 1.3 miles laterally and 1,000 feet vertically.
The FAA noted that the alerts do not indicate an imminent collision risk but instead predict a potential conflict based on current flight paths.
No further details were provided by the FAA. All three flights, while delayed, landed at their destination of Dallas-Fort Worth International Airport.
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UPS and United Airlines referred all questions to the FAA. FedEx has not yet responded to NBC 5's request for comment.
