The close call between the United and Delta flights at the Phoenix airport comes amid an increase in plane near-collisions.

The Federal Aviation Administration is once again looking into a close call at a major U.S. airport, after two passenger jets narrowly avoided a mid-air collision as they attempted to land in Phoenix.

A United flight from San Francisco and a Delta flight from Detroit came within 425 feet of each other in the sky, according to flight radar data. NTSB guidelines say plans should always stay at least five miles apart.

The two flights, United Airlines Flight 1724 and Delta Air Lines Flight 1070 came too close to each other while arriving at the airport.

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 plane left the Lehigh Valley International Airport in Allentown, Pennsylvania, around 5:24 a.m. and was expected to arrive at Chicago's O'Hare International Airport at 8:44 a.m.

The FAA has begun an investigation into a midair incident involving a United Airlines Boeing 737-900ER and a Delta Air Lines Airbus A330-300.

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

The aircraft landed safely and the incident is being investigated by the Federal Aviation Administration (FAA), officials said.

Both aircraft were inbound to the airport when a loss of separation occurred during their approach for landing

The FAA is investigating a near-miss incident involving a United Airlines and a Delta Air Lines flight at Phoenix Sky Harbor International Airport,

Two days before Christmas, a group led by President-elect Donald Trump's chief architect of immigration policy wrote to state, county and city officials in so-called "sanctuary" jurisdictions to threaten criminal prosecution,