A major failure in the U.S. air traffic control system caused widespread flight disruptions Monday, September 21, grounding aircraft at some of the nation’s busiest airports and producing delays and cancellations that continued into Tuesday.
The problem originated at a Federal Aviation Administration air traffic control facility in Philadelphia, where a primary telecommunications circuit failed Monday morning. When the system attempted to switch to its backup, officials discovered that a fiber-optic cable in New Jersey had been accidentally severed during construction work. The dual failure temporarily deprived controllers of critical radar and communications capabilities.
The FAA imposed ground stops affecting Philadelphia International, Newark Liberty, John F. Kennedy and LaGuardia airports, with disruptions also reaching Boston and other airports as congestion spread through the national network.
Newark was particularly hard hit. More than 600 flights into or out of the airport were canceled Monday, and commercial arrivals essentially stopped for nearly eight hours. Philadelphia recorded more than 200 cancellations, while delays and cancellations rippled across the country. More than 100 aircraft were reportedly diverted to alternate airports.
The timing compounded the disruption, with approximately 130 world leaders traveling to New York for the United Nations General Assembly.
Repairs were completed Monday evening and normal operations began resuming, although residual delays and cancellations continued Tuesday as airlines repositioned aircraft and crews.
The incident also renewed concerns about the resilience of the nation’s aging air traffic control infrastructure. The same Philadelphia FAA facility experienced significant communications failures affecting Newark in 2025 and is among the systems targeted for modernization.