( CNN ) -- American Airlines grounded flights nationwide on Tuesday due to problems over several hours with its computerized reservation system . The decision also resulted its regional affiliate , American Eagle , holding flights at Dallas Ft. Worth , Chicago 's O'Hare and New York LaGuardia -- all major airports for the carrier 's domestic operations . The glitch caused big delays and flight cancellations for the company , which sought court approval on Monday to exit bankruptcy . It plans to merge with US Airways . American CEO Tom Horton apologized the customers in a video Tuesday evening , saying that the glitch was `` a software issue impacting both primary and backup systems . '' Bad weather often forces airlines to halt flights in specific regions , but a nationwide grounding is highly unusual . American estimates it flies about 275,000 passengers a day and receives more than 239,000 reservations calls . American first reported computer problems via twitter at noon ET , then announced a ground stop one hour later . Its reservation systems were restored by 4:30 p.m. , but the company said passengers could expect delays and cancellations throughout the day . The Federal Aviation Administration also confirmed that American had sought permission to hold flights . The carrier said in a statement that it saw `` no evidence '' that the technical outage was in any way related to Monday 's deadly bombing in Boston that is under investigation as an act of terrorism . Airlines have long been a target of overseas terrorists , although U.S. officials say they have not determined whether the origin of the Boston attack was domestic or foreign . American 's reservation systems are operated by the technology company Sabre , which told CNN that its systems were functioning , but American had trouble connecting . DFW , where American operates 85 % of daily flights , used buses to help get passengers off planes because gates were full of aircraft that had not departed , spokesman David MagaÃ±a said . Inside the terminal there were some longer lines and the airport was more crowded than it would be on a day with normal operations . The carrier apologized to passengers and said they could rebook on another airline if they must travel on Tuesday and were already at the airport . American was also willing to honor fare differences for rebooked travel , in certain cases , or offer refunds in other circumstances . CNN 's Devon Sayers and Mike Ahlers contributed to this report .
NEW : American CEO apologizes , says the glitch affected the backup system , too . Nationwide move is very unusual for a major U.S. airline , big delays . Grounding also impacted American 's regional partner , American Eagle . NEW : American said it saw no link between its problems and events in Boston .