Atlanta , Georgia ( CNN ) -- The failed computer system that caused flight delays across the country has been restored , the Federal Aviation Administration said Thursday . FAA spokesman Paul Takemoto said the system went out at 5:06 a.m . ET and came back on about five hours later . He said officials working to pinpoint the cause know that there was a problem with the main telecommunications systems . `` It was an efficiency problem rather than a safety problem , but it was a serious efficiency problem , '' Takemoto said . Due to the outage , air traffic controllers had to enter flight plans manually , a problem that causes delays , according to the FAA and the National Air Traffic Controllers Association . The air traffic controllers ' group said the problem will cause flight delays throughout the day because of a `` domino effect . '' `` Air traffic controllers are without electronic decision-making tools and can not keep up with the sheer numbers of flights -- resulting in delays , '' the controllers ' group said in a statement during the outage . `` Air traffic controllers on the ground at major airports are getting no automated flight plan information and have to enter that information manually , a cumbersome and time-consuming process . '' Carmen McDonald was among those passengers inconvenienced by flight delays when the computerized system that airlines use to file flight plans failed for several hours Thursday in Atlanta , Georgia , and Salt Lake City , Utah . McDonald said she thought her Spirit Airlines flight would leave on time around 7 a.m . ET from Fort Lauderdale , Florida . But the 39-year-old model sat for an hour and 15 minutes amid the noise of loud kids before the plane was ready to leave a logjammed runway and take off to Boston , Massachusetts . `` I 'm frustrated , '' she said , distracted by using Twitter and calling on her cell phone as her plane sat planted on the runway . `` I have somewhere to be . '' iReporter records video from tarmac . AirTran Airways spokesman Christopher White said the airline had canceled 22 flights around the country as of 8 a.m . ET and had delayed dozens more because of the flight plan filing system problem . He said most of the canceled flights were in Atlanta , AirTran 's hub of operations , and others are spread throughout the country . White said the problem will have `` a pretty major impact on operations '' and the cancellations will have a ripple effect . `` We will be a mess all day , '' he said . AirTran , which operates about 700 flights a day , asked customers to check airtran.com before showing up at the airport . Delta Air Lines spokeswoman Susan Elliott said the airline was not providing numbers on how many flights were affected . But she said that Delta will give travelers some flexibility in rescheduling . American Airlines spokesman Tim Smith said that 300 to 500 flights had been delayed , virtually every one scheduled for takeoff . The longest delays have been a little more than an hour , but no flights have been canceled , and some might be consolidated , he said . `` Things are moving ; they are just moving more slowly , '' Smith said , adding that American has been affected at LaGuardia and John F. Kennedy International airports in New York as well as in Dallas/Fort Worth , Texas , and Chicago , Illinois . Smith said the problem reflects that the U.S. air traffic control system operates with what he calls `` 1960s technology '' and needs to be modernized . US Airways spokesman Morgan Durrant said the airline had a few delays across the system , including some as long as 30 minutes but it does n't anticipate any more . Hartsfield-Jackson Atlanta International Airport said officials there were `` monitoring the situation regarding the FAA 's automated flight plan system . '' `` The airport is working to minimize the impact on customers by bringing in additional staff and ensuring that all facilities are operational and fully maintained . All passengers are encouraged to contact the airlines regarding the statuses of their flights before they head to the airport , '' the airport said . At Indianapolis International Airport , most morning flights left on time with little impact from the computer glitch , but inbound flights from large hubs are expected to be delayed Thursday and possibly into Friday , said spokeswoman Susan Sullivan . The airport asked concessionaires to beef up staffing levels and has added employees to keep the facility clean and the passengers comfortable . The system -- the National Airspace Data Interchange Network , or NADIN -- appears to be the same one that failed in August 2008 . The FAA said the information in the network is data required to launch planes expeditiously . Airplane safety was not affected , the FAA said , adding that planes in the air had radar coverage and communication . Weather also might have played a role in Northeast flight delays . The air traffic controllers said `` weather equipment was affected '' and information such as winds speeds was not `` processing . '' The controllers said that `` airport efficiency is being cut at least [ in ] half at places like New York-JFK '' and that in the `` New York airspace , controllers are forced to put 20 miles of space between aircraft . '' CNN 's Mike Ahlers , Jeanne Meserve and Joe Sterling contributed to this report .
NEW : Air traffic controllers ' group says problem will cause delays throughout day . NEW : FAA says officials working to pinpoint cause of computer system glitch . `` I 'm frustrated . I have to be somewhere , '' delayed passenger says . Air safety not compromised , FAA says .