An outage briefly left air traffic controllers “unable to see, hear, or talk to” planes last week, a union spokesperson said.

The root cause is an air traffic controller shortage, a nationwide issue the Trump administration has pledged to fix.

NEWARK, N.J. (AP) — Flight delays and cancellations persisted at Newark Liberty International Airport Monday, with Senate Minority Leader Chuck Schumer calling for an investigation into the “chaos” sparked by an air traffic controller shortage and thick cloud cover.