More than 3,700 flights are gone.

WASHINGTON — Major airlines canceled more than 3,700 U.S. flights on Saturday and delayed 2,000 more. Reuters reported the count as the country tried to recover from the longest nationwide halt of departing flights since the attacks of Sept. 11, 2001. The cancellations and the delays are one Saturday count. They are not added to Friday.

Friday is a separate count. Reuters reported that the Federal Aviation Administration’s ground stop halted nearly all departing flights for almost five hours, and that airlines then canceled nearly 10,000 flights and delayed more than 7,000 others. A Reuters dispatch from Friday night, citing Flightradar24, said that by 11:30 p.m. nearly 10,000 flights had been canceled, more than 2,200 each at Delta and at American, and 1,800 at United. Those airline figures sit inside the Friday total. They are not added to Saturday’s 3,700.

This is an emergency.

Transportation Secretary Sean Duffy said the airspace reopened at 8:15 p.m. Eastern on Friday. “It’s going to be slow,” he told reporters at the White House. On the money, Reuters reported that Duffy called for $50 billion to upgrade air traffic control, up from $30 billion he had sought earlier. “This is an emergency,” he said. He said the trouble began at 3:36 p.m. Eastern, when air traffic control centers saw instability in radar and in communications.

Reuters, in a separate dispatch, reported that Duffy later attributed the outage to the FAA’s legacy network: switches and routers overloaded with data and went down. What overloaded them was not clear. The same dispatch said the White House and the Transportation Department had asked Congress the same day for another $30.1 billion to upgrade airports and air traffic control, including $10.1 billion for the control system. The $50 billion and the $30.1 billion are two figures in two Reuters dispatches. This desk does not fold them into one.

Two airline officials told Reuters the outage appeared to be hitting a network that carries the radio frequencies controllers use to talk to pilots. Reuters named the contractor that oversees that network: L3Harris. That is what the officials said. It is not a finding. Mullin said there was “zero evidence” so far of a cyberattack or of a rogue artificial-intelligence system, and that investigators had not ruled either out. “It appears this was mechanically driven. However, we’re still looking,” he said.

The photograph is Friday night, Nov. 13, at the White House. Duffy is speaking. His mouth is open. His right hand is up. Markwayne Mullin, the homeland security secretary, is standing beside him, also pointing. Elizabeth Frantz, Reuters. It is not Saturday morning, and it is not an airport.