The airline told the Sun the e-mail was sent to passengers who have upcoming flights to or through Newark’s airport, as well as its MileagePlus

The crucial travel hub for United is still struggling to recover from air traffic control glitches that have already disrupted hundreds of flights.

Caught in the middle of the issues at Newark is United Airlines, which is the most active airline at the New Jersey airport. While the problems lie with the FAA system, the airline is where people often aim their frustrations over cancellations and delays.

When you have to communicate effectively in a tough situation, pick the most important message and stick with it.

"We've turned the corner, and we have the commitment," United Airlines CEO Scott Kirby said of reforms to the Federal Aviation Administration.

One air traffic controller (ATC) and a trainee will operate every flight in and out of Newark between 6.30pm-9.30pm — despite 15 staffers being the standard requirement for a shift.

Three incidents at Newark have shaken the public. Meanwhile, the FAA is understaffed. Here's what the Trump administration wants to do about it.

Newark Liberty International Airport is facing another FAA-imposed ground delay due to staffing shortages, after a telecommunications issue led to delays on Sunday.