Air travel across the U.S. Northeast was thrown into disruption this week after a communications failure at a Federal Aviation Administration facility in Philadelphia temporarily affected air traffic operations at several of the region’s busiest airports.

The incident began Monday, September 21, when a failure on a primary communications circuit at the FAA facility was followed by the discovery that a backup fiber-optic line had also been severed. Without the normal communications and radar connections, air traffic controllers were unable to manage flights at full capacity, forcing the FAA to impose ground stops and other restrictions.

The disruption affected major airports including Newark Liberty International Airport, John F. Kennedy International Airport, LaGuardia Airport, Philadelphia International Airport and Boston Logan International Airport.

Although the technical problem was repaired Monday evening, the disruption created a backlog that continued affecting travelers into Tuesday.

What Caused the Outage?

The incident was not caused by severe weather or a cybersecurity attack. It resulted from failures involving telecommunications infrastructure serving the FAA's Philadelphia air traffic control operation.

According to the FAA and reports from transportation officials, the primary communications circuit failed Monday morning. When controllers attempted to switch to the backup system, they discovered that a fiber-optic line had been accidentally cut during construction work in New Jersey. Officials initially differed over which construction crew was responsible, with Amtrak and New Jersey Transit issuing different accounts.

The combination of the two failures left controllers without important radar and communications capabilities for several hours.

Newark experienced one of the most severe impacts. Commercial air traffic there effectively stopped for much of the day, with no commercial flights landing between approximately 9:40 a.m. and 5:20 p.m. More than 600 flights into and out of Newark were canceled, according to flight-tracking data cited by the Associated Press. Philadelphia also recorded more than 200 cancellations, while LaGuardia and JFK experienced significant disruption.

Why the Disruption Continued After Repairs

Restoring the communications system did not immediately return the region's aviation network to normal.

Major airports operate on tightly connected schedules. When hundreds of flights are canceled or held on the ground, aircraft and crews can end up in different locations from where airlines originally planned. Passengers also miss connecting flights, creating additional demand for limited seats on later services.

Boston Logan faced another complication. The airport was already operating under a ground-delay program, with ongoing runway construction adding to capacity constraints. More than 400 flights were delayed there Monday, according to Boston.com.

The FAA said Tuesday that low clouds, reduced visibility and wind could continue contributing to delays around New York airports, meaning some travelers could experience disruption even after the communications failure itself had been resolved.

What Travelers Should Do

For passengers flying through the Northeast, the most important step is to check directly with the airline before leaving for the airport.

The FAA has advised travelers to monitor their flight status because schedules can continue changing as airlines work through the backlog. Some airlines also offered affected passengers opportunities to change flights without the usual fees, depending on the itinerary and travel dates.

Travelers with connecting flights should also allow additional time and check the status of every segment of their journey rather than assuming that a flight showing as scheduled will operate normally.

The incident has also renewed attention on the condition of America's air traffic control infrastructure. Transportation Secretary Sean Duffy has argued that the disruption demonstrates the need for greater investment in modernizing the country's aviation systems.

For passengers, however, the immediate issue is simpler: the major communications failure has been repaired, but its effects can take time to work through the system. Anyone traveling through the Northeast in the days following the outage should continue checking airline and FAA updates before heading to the airport.