American Airlines requested a nationwide ground stop, which was later canceled, on the morning of Christmas Eve due to technical problems.

Following a brief outage that grounded all American airlines flights during one of the busiest travel periods of the year, American Airlines says it has resumed service Tuesday morning, albeit with substantial delays.

Flights were grounded for about an hour on Christmas Eve, one of the busiest travel days of the year, before the airline restored its systems. But heavy delays are expected.