AMERICAN AIRLINES HALTS FLIGHTS, PASSENGERS STUCK

DALLAS (AP) -- American Airlines grounded flights across the country Tuesday because of an outage of its main reservations system. Thousands of passengers were stranded at airports and on airplanes.

A spokesman for the Federal Aviation Administration said American asked to halt its flights until 5 p.m. EDT.

Flights into American's five biggest cities - New York, Dallas, Los Angeles, Chicago and Miami - are stopped until 5:30 p.m. EDT.

"Any American plane sitting on the ground anywhere in the U.S." won't be taking off, said FAA spokesman Lynn Lunsford.

Flight-tracking service FlightAware estimated that about 900 flights would be delayed if American resumed flying at 5 p.m., and the cascading effect would cause another 800 delays Tuesday evening because planes and crews wouldn't be where they were needed.

Customers couldn't make reservations or rebook if their flight was cancelled. Passengers described long airport lines and frustration at the lack of information from airline employees

SOURCE: PRESSURE-COOKER BOMBS USED IN BOSTON BLAST

BOSTON (AP) -- The bombs that ripped through the Boston Marathon crowd were fashioned out of ordinary kitchen pressure cookers, packed with nails and other fiendishly lethal shrapnel, and hidden in duffel bags left on the ground, people close to the investigation said Tuesday.

President Barack Obama branded the attack an act of terrorism, whether carried out by a solo bomber or group, and the FBI vowed to "go to the ends of the Earth" to find out which it was.

Scores of victims remained in Boston hospitals, many with grievous injuries, a day after the twin explosions near the marathon's finish line killed three people, wounded more than 170 and reawakened fears of terrorism. A 9-year-old girl and 10-year-old boy were among 17 victims listed in critical condition.

Officials zeroed in on the nature of the bombs, discovering they were made of common 1.6-gallon pressure cookers, one containing shards of metal and ball bearings, the other packed with nails, and both stuffed into duffel bags, said a source close to the investigation.

FACEBOOK BRINGS 'CHAT HEADS' FEATURE TO IPHONE APP

NEW YORK (AP) -- Facebook has updated its iPhone and iPad applications to let people keep using its chat feature even when they are doing other things, such as reading friends' updates.

Facebook Inc. also said Tuesday that it's bringing its "chat heads" feature to its Apple apps. It's called chat heads because friends' profile photos pop up when they send you a message.

Chat heads is part of a broader integration that Facebook is doing with a new Home app on some phones running Google's Android operating system.

Unlike with Home, iPhone and iPad users will have to stay inside the Facebook application to use chat heads. The update is already available in Apple's App Store, but Facebook says the chat heads feature will roll out in the coming weeks.