Flights resume, but situation remains tense

Passengers trickled into New York's LaGuardia airport Thursday morning. Federal officials later in the day closed all three of New York's major airports.

(CNN) -- Most U.S. airports and airlines resumed operations on Thursday, but not without a host of cancellations, arrests and anxious passengers.

The most trying moments came in New York, site of one of Tuesday's terror attacks.

At least eight people were arrested Thursday at John F. Kennedy and LaGuardia airports, law enforcement sources said, including four who previously were challenged at one of the airports on Tuesday, the day terrorists commandeered four other planes.

AIRPORT OPENINGS Click for the status of major U.S. airports  CNN.COM SPECIAL REPORT  CNN NewsPass Video  Agencies reportedly got hijack tips in 1998  MORE STORIES Intelligence intercept led to Buffalo suspects Report cites warnings before 9/11  EXTRA INFORMATION Timeline: Who Knew What and When? Interactive: Terror Investigation Terror Warnings System Most wanted terrorists What looks suspicious? In-Depth: America Remembers In-Depth: Terror on Tape In-Depth: How prepared is your city?  RESOURCES On the Scene: Barbara Starr: Al Qaeda hunt expands? On the Scene: Peter Bergen: Getting al Qaeda to talk AIRLINE PLANS AirTran -- Resuming limited flight schedule Thursday Alaska Airlines -- Limited flights, starting Thursday afternoon. America West -- Resumed some flights at 3 p.m. EDT Thursday. American Airlines -- American and American Eagle planned to resume operations at 4 p.m. EDT Thursday. American Trans Air (ATA) -- resumed "partial scheduled service" Thursday Continental Airlines -- Limited flights Thursday. Delta Air Lines -- Began limited operations noon Thursday Frontier -- Flights canceled until at least 6:45 a.m. EDT Friday Northwest Airlines -- Resuming limited schedule at 7 p.m. EDT Thursday. Southwest -- Resumes scheduled flights at noon EDT Friday. TWA -- Resuming flights at 4 p.m. EDT Thursday United -- No scheduled flights until 9 a.m. EDT Friday. U.S. Airways -- Partial service, starting at 3 p.m. EDT Thursday. MORE STORIES Passengers can expect tight security, long waits     RESOURCES Click for the FAA's full list of airport openings

The suspects were booked as passengers on flights from Kennedy or LaGuardia airports on Thursday, the sources said. At Kennedy, one suspect was removed from a plane and two others -- including a man with a phony pilot's license -- were taken into custody at a pilot's lounge.

Asked if this was seen as another hijacking attempt, one U.S. official said, "Certainly, this is being looked at -- that a hijacking was thwarted. There is concern in our office that this may have been another attempt."

The suspects were taken into custody for carrying fake documentation -- including the one man carrying the fake pilot's license -- and immigration issues, the sources said.

The Federal Aviation Administration, which had allowed airports that met strict security guidelines to reopen Thursday morning, ordered all three of New York's major airports closed around 5:30 p.m. Thursday.

Northwest Airlines, meanwhile, canceled all its Thursday flights because of "external information … that indicates that it is not prudent to fly this evening," spokeswoman Mary Beth Schumbert said.

And Washington's Ronald Reagan Airport was closed all day "due to the airport's proximity to key federal installations in the Washington, D.C., area including the Pentagon," the FAA said.

The Transportation Department had allowed domestic flights to resume for the first time since Tuesday morning at 11 a.m. EDT Thursday, but air travel was limited.

"The reopening of our national airspace is good news for travelers, for the airlines and for our economy," Transportation Secretary Norm Mineta said in a written statement.

"But I must caution everyone that a system as diverse and complex as ours cannot be brought back up instantly. We will reopen airports and resume flights on a case-by-case basis, only after they implement our more stringent levels of security."

Attention given to certain flights

Many airlines said they would devote most or all of their efforts Thursday to completing flights that were diverted Tuesday after the terrorist hijackings and plane crashes in New York, Washington and rural Pennsylvania.

No international carriers were being allowed in from overseas. Only American-based airlines were being allowed to fly into the United States from abroad.

However, dozens of international flights that had been diverted were allowed to fly into the United States because they had been thoroughly searched while on the ground in Canada, officials said.

Many of the day's first flights did not even contain passengers. Officials at Atlanta's Hartsfield International Airport said about 12 planes have arrived but none with passengers. Airlines were repositioning planes and crews in preparation for resuming normal schedules.

Delta, which is headquartered in Atlanta, usually has 900 daily flights in and out of the airport, but fewer than 5 percent were expected to proceed Thursday.

"We want to stress that things will move slowly," Benjamin DeCosta, Hartsfield's general manager, told CNN. "We have new security procedures in place and we want people to bring with them their confirmed reservations, tickets, and their patience."

At midafternoon Thursday 1,200 flights were in the air, primarily diverted and repositioning flights, said Carol Hallett, president of the Air Transport Association, who said she is telling people the skies are now completely safe.

Stranded passengers are getting some assistance from Amtrak, which is increasing the capacity of its runs between Boston and Washington and honoring plane tickets.

Tighter security guidelines

Many airports reopened soon after the flight ban was lifted, but others were slow to do so as officials worked to meet new tighter security guidelines.

Those measures include a ban on all knives, the elimination of curbside and off-airport check-ins, the use of federal air marshals, and a prohibition of all but ticketed passengers beyond airport metal detectors. Passengers also will be required to go to ticket counters to check in.

Travelers were encouraged to contact airlines to determine when or whether their flights would operate on schedule and to prepare for delays at the airports.

The FAA's Web site -- www.faa.gov -- offered information on what airlines and airports are operating.

Among the airlines that were resuming a limited number of flights Thursday were American and United, which each lost two planes to hijackers Tuesday. Also, Delta, Continental and U.S. Airways planned to put a number of planes in the air.

Southwest Airlines said it was not resuming its flights Thursday.