Newark Liberty International Airport is one of the largest hubs of United Airlines, and the congested airport is also the Chicago-based carrier's biggest operational challenge. The company told 1.5 million customers in a note on Thursday that congestion at Newark has eased since it reduced flights there.

Amid dire conditions at the airport, an airline operations crew has had to figure out how to get more than 600 flights a day to take off and land without incident.

United Airlines slashes Newark flights amid FAA staffing issues, aiming to reduce delays and improve summer travel reliability.