Incoming flights to Philadelphia International Airport were grounded Monday morning after the Federal Aviation Administration detected an equipment failure at an air traffic control facility, officials said. The problem caused widespread delays and cancelations at airports along the East Coast, but regular air travel has resumed in Philly.

The ground stop at PHL took effect around 9:48 a.m., leaving planes that were bound for Philadelphia idling on runways throughout the region. Outgoing flights were delayed by an average of an hour at PHL for much of the afternoon, the FAA said, and ground stops also were issued for all domestic flights traveling to Newark Liberty International Airport and Teterboro Airport in Bergen County, New Jersey.

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FAA Administrator Bryan Bedford said the problem was caused by a blown circuit at Philadelphia's Terminal Radar Approach Control facility, which houses a control room and air traffic control tower that serves much of the approaching and departing flights within a 50-mile radius. A backup line in New Jersey failed to boot after an Amtrak crew accidentally cut the line at a construction site, officials said.

"We discovered that the backup fiber had a break, and that fiber break is probably 13 hours to repair," Bedford said. "It's massive, I'm told. ​Meanwhile, we've got the new circuit ​ready to install now."

The broken telecom circuit led the FAA to restrict air traffic at New York's LaGuardia and JFK International airports and Boston's Logan International Airport on Monday, causing delays to more than 1,000 flights on the East Coast.

U.S. Transportation Secretary Sean Duffy said normal service began to return at PHL and LaGuardia as of about 2:45 p.m. Flights into Newark, JFK and Teterboro airports remained paused.

A spokesperson for PHL said travelers should continue to expect delays, especially for inbound flights to Philly.

"Arriving flights are delayed an average of 212 minutes," PHL spokesperson Heather Redfern said in a statement. "Departing flights are also seeing delays averaging about 60 minutes. We advise anyone with plans to fly to or from PHL today to check with their airlines for the most up to date flight information."

PHL had nearly 900 flights scheduled for Monday. About 370 flights were delayed and another 130 were canceled as of Monday afternoon. Across the country, nearly 4,000 flights were delayed and about 500 were canceled.

Last year, the air traffic control facility that handles flights in and out of Newark suffered several telecommunications outages, and Philadelphia's TRACON facility experienced outages affecting communications and radar. After the string of incidents, Congress approved $12.5 billion for upgrades to the air traffic control systems and to hire more air traffic controllers. 

Bedford said earlier this month the FAA will need billions in additional investments to modernize the nation's air traffic control system.