UPDATE 7-American Airlines resumes flights after brief grounding ahead of busy Christmas travel

Adds details on travelers stranded, glitch, cancellation data in paragraphs 1-4, 10-14

By Utkarsh Shetti, Abhijith Ganapavaram and David Shepardson

Dec 24 (Reuters) - American Airlines AAL.O said on Tuesday its flights had resumed after a technical glitch forced the carrier to issue an hour-long ground stop, disrupting travel for thousands on Christmas Eve, one of the busiest periods of the year.

The airline said a vendor technology issue briefly affected its ability to get planes in the air.

While customers across social media were still pressing for details on their delayed flights, the relatively brief stoppage means American will likely avoid a full-scale meltdown that ripples for days during the holiday season.

"Not a good start to Christmas Eve travel as current flight is grounded and Captain cannot provided ETA on resolution from system outage and/or paperwork error at national level. Will make connections or refunds more complicated too," a user said, tagging American Airlines on X.

Shares of the carrier were down 2% in early trade.

It is the latest technical snag after carriers were hit by a global tech outage tied to Microsoft's MSFT.O Azure cloud platform and a software issue at cybersecurity firm CrowdStrike CRWD.O earlier this year.

The outage had cost Delta Air Lines DAL.N at least $500 million.

Two years ago, Southwest Airlines LUV.N experienced a meltdown with its systems during the holidays that led to 16,900 flight cancellations and stranded 2 million passengers. It was eventually fined $140 million in the largest-ever civil penalty for a travel disruption.

Airlines have upgraded their cybersecurity and operational software systems but given there was an exodus of talented workers during the pandemic, the glitches over the last few years are not altogether unexpected, said Ken Quinn, partner at law firm Clyde & Co.

American Airlines operates thousands of flights per day to more than 350 destinations in more than 60 countries.

The U.S. Federal Aviation Administration in a statement on Tuesday referred Reuters to the carrier, reiterating that the carrier had reported a technical issue.

American Airlines, along with its wholly owned regional carriers in the U.S., has canceled over 23,000 flights or about 1.3% of their scheduled flights this year, according to FlightAware data.

The travel disruption comes as the Transportation Security Administration expects to screen a record 40 million passengers over the holidays.

(Reporting by Utkarsh Shetti in Bengaluru; Editing by Shilpi Majumdar and Sriraj Kalluvila)

((UtkarshUmesh.Shetti@thomsonreuters.com;))