Free flights after United website error

United Airlines said it's reviewing whether to honour an unknown number of tickets accidentally offered online for free after faulty data was put into its reservations system.

The $0 fares were only on the United.com website for "a couple hours" at midday and weren't distributed via channels such as travel agencies, said Megan McCarthy, a spokeswoman for the unit of Chicago-based United Continental. United's Shares reservation system didn't cause the fault, she said, without giving further details.

"For a time, we closed the booking engine on United.com so we could correct the error," McCarthy said. The website was back to normal at about 2.30pm Chicago time, she said.

Many of the tickets cost $US5 ($A5.40) or $US10 in total, suggesting that United was only collecting a mandatory 9/11 security fee of $US2.50 per leg, said Rick Seaney, chief executive officer of FareCompare.com, a ticket research firm based in Dallas. Taxes and fees typically add up to $US22 or more a ticket, he said.

McCarthy said she had no information about when United would decide on whether to accept the tickets for travel, or on what trips the fares had been made available.

A similar pricing mistake occurred in May 2002 when a fare sale accidentally appeared as a $5 round-trip ticket for about 45 minutes, the Chicago Tribune reported at the time.

Today's incident was at least the fourth public computer disruption at United since March 2012, when the carrier switched its former Apollo reservation system over to Shares, the program used by merger partner Continental Airlines. United's former parent, UAL Corp., combined with Continental in October 2010.

In the reservation shift, United struggled with long lines at airport check-in counters and a surge in call volumes while making the transition.

Automated check-in access was lost at airport kiosks and on United's website in August 2012, and a software breakdown in the carrier's flight dispatching system delayed hundreds of flights in November.

Bloomberg