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

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 investigating after two planes nearly collided at Phoenix Sky Harbor International Airport. >> Live, local, breaking. Download the 12News app United Airlines Flight 1724 and Delta Air Lines Flight 1070 were preparing to land around 11 a.

Images show United and Delta jets coming dangerously close to each other while landing in Phoenix, Arizona. Andrew Taylor, 70, said he would've had to continue working if he'd stayed in the US. Some older Americans are still working because they can't afford to retire.