A blown circuit and a severed backup cable at Philadelphia air traffic control halted flights at Newark, Philadelphia and Teterboro for about seven hours Monday, Sept. 21

FAA Administrator Bryan Bedford said the backup line was found cut at a New Jersey construction site; ground stops later expanded to JFK and LaGuardia, and departure delays ran up to 150 minutes.

The circuit. A circuit that carries radar and communication data for the Philadelphia air traffic control facility blew Monday morning, Sept. 21. When the backup cut in, officials found the backup line severed at a New Jersey construction site. The ground stop. With controllers short of working frequencies, the FAA's only lever was to stop traffic: a ground stop at Newark Liberty, Philadelphia International and Teterboro around 10 a.m., then an expansion to JFK and LaGuardia while Northeast airspace closed for at least 30 minutes to swap the circuit. The swap did not take, leaving Newark and Philadelphia halted into the afternoon with no estimated resumption time. Departure delays ran up to 150 minutes. The fiber. Verizon, which owned the fiber, said construction contractors working beside an Amtrak rail line dug up and cut its cable and that "Verizon bears no responsibility for this incident." The reopening. Transportation Secretary Sean Duffy said the lines were repaired and Northeast flights were resuming shortly after 5 p.m., about seven hours after the first ground stop. (TS: That's a liability position, not a finding — no agency has said who pays for 900-plus canceled flights.) "FAA technology outage is affecting all airlines in the Northeast... Flights that had been destined for Newark have either been held at their departure airport or diverted to alternative airports." — United Airlines Still open. No one has said who cut the cable — Duffy blamed an Amtrak crew, Amtrak pointed to a New Jersey Transit contractor, NJ Transit said its crew severed a cable at 9:45 a.m. but suggested a Verizon crew may be at fault. No investigative agency has been named.

What GAO told the FAA to fix, and DOT agreed to:

The Department of Transportation agreed to all nine recommendations in the GAO report released the same day, Monday, Sept. 21
GAO found the FAA had completed no formal risk assessment for seven of the eight aviation communication systems it reviewed
FAA work with industry partners fully met 2 of 8 leading practices for collaboration and partially met the other 6

Newark canceled more than 300 flights Monday, more than any airport in the world that day

That was over half of Newark's scheduled departures, and United canceled all its remaining domestic mainline and United Express flights there Monday afternoon.

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