Is this the first such case since 9/11?

No.

"January 11, 2023. All U.S. departing flights were halted for several hours after a computer outage crashed the FAA's Notice to Air Missions (NOTAM) pilot notification system"

9/11, 2023 and today are the only three times.

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luxuryballs 2 hours ago | parent [-]

July 19th 2024 crowdstrike/microsoft update issue halted a bunch of (all?) flights in the US also (coincidentally 6 days after presidential assassination attempt)

	▲	echoangle 2 hours ago \| parent [-]
		Not due to a requirement by the FAA but by the airlines being dependent on their windows computers, right? Legally, you were still allowed to fly, I think.

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Jtsummers 6 hours ago | parent | prev | next [-]

9/11 was different, that also required all planes to land, more or less, as quickly as possible and not continue to their destinations (unless that was timely, I suppose). This one is a departure ground stop, no more planes going up. Planes in the air haven't been ordered to land yet.

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KPGv2 6 hours ago | parent | prev [-]

no, there was one in 2023 when a pilot notification system went down