Two United Airlines planes clipped wings at San Francisco International Airport early Tuesday morning while preparing for take off, according to the Federal Aviation Administration.

In a statement, the Federal Aviation Administration said United Flight 863 heading to Sydney, Australia and United Flight 877 bound for Hong Kong were the two planes involved. Flight 863’s left wingtip collided with the right wingtip of Flight 877 about 12:35 a.m., the FAA said.

The United planes clipped wings as one of the planes pushed back from the gate. The incident comes amid a growing crisis at Newark Airport, caused in part by a shortage of air traffic controllers.