Delta Air Lines cancels 5,000 flights since tech outage

Delta Air Lines struggled to restore normal operations after last week's crippling global cyber outage, cancelling 1,250 flights beyond the 3,500 it had already scrapped.

The issue has stranded thousands of Delta travellers across the United States, with some having to rent cars to drive hundreds of miles while others could have to wait days for new flights or cancel trips altogether.

The Atlanta-based airline, which canceled a third of its schedule and delayed another 1,700 flights or 44 per cent, according to FlightAware, is battling operational issues after the outage hit its crew tracking system.

Delta has offered no timetable for resumption of normal operations and has already cancelled another 305 flights for Monday, the flight tracking website said. Its total of cancelled flights since Friday now stands at more than 5,000.

A software update by global cybersecurity firm CrowdStrike triggered system problems for Microsoft customers, including many airlines, on Friday.

Although other US airlines have largely recovered, Delta has struggled to return to normal. United Airlines canceled 9 per cent - or 266 - of Sunday's flights, the second most among carriers.

Delta CEO Ed Bastian said the issue affected its Microsoft Windows systems, snarling a critical application.

"In particular one of our crew tracking-related tools was affected and unable to effectively process the unprecedented number of changes triggered by the system shutdown," Bastian told customers in an email.