The United and Delta flights were less than a quarter of a mile apart horizontally before the warning devices went off, officials say.

The Federal Aviation Administration is investigating a narrowly missed midair collision between a United flight and a Delta flight at Phoenix Sky Harbor International Airport on Saturday, the agency said.

The FAA has launched an investigation into a loss of separation between two commercial flights in Phoenix Saturday.

The Federal Aviation Administration is investigating after a United Airlines flight and a Delta Airlines flight had a near-collision over Phoenix on Saturday.

Delta Air Lines and United flights come close when both attempt to land at Phoenix Sky Harbor International Airport

A Delta Air Lines plane and a United Airlines aircraft raised alarms when they flew too close to each other while flying into Phoenix on Saturday. The Federal Aviation Administration is investigating the “loss of required separation” incident.

At the same time, a similar alert was set off on a United Flight 1724 from San Francisco, carrying 123 ... according to FlightRadar24. The FAA noted both planes landed safely "after experiencing ...