BOSTON -- Amid new anxiety about air travel and tough new regulations about what passengers may bring on planes, at least seven U.S. flights yesterday were involved in security incidents. In one case, a stick of dynamite was found to have been aboard a flight.

The rash of events, safety consultants and others said, reflected both heightened emotions and appropriately tightened security in the wake of an alleged plot to blow up trans-Atlantic airliners that was thwarted earlier this month by British authorities.

"I think it's a combination of both," said Douglas Laird, a Reno, Nev.-based consultant to the airline industry and former longtime security director for Northwest Airlines. "I think there is a heightened awareness of what happened in London, and that causes some people to overreact."

In what may have been yesterday's most serious incident, authorities said a college student's checked luggage on a Continental Airlines flight from Argentina was found to contain a stick of dynamite after it landed in Houston en route to Newark, N.J.

A bomb-sniffing dog at the international arrivals area at George Bush Intercontinental Airport detected an explosive substance in a suitcase belonging to a man who told Houston authorities that he works in mining and often handles explosives.

The flight continued to Newark without the man or his baggage, and officials said it was swept again for explosives upon landing as a precaution.

Three U.S. aircraft -- one each from American Airlines, U.S. Airways and Continental Airlines -- made emergency landings yesterday.

A Transportation Security Administration spokesperson said American Airlines Flight 55, bound for Chicago from Manchester, England, was diverted to Bangor, Maine, because of "a reported threat to the aircraft while it was en route."

FBI spokeswoman Gail Marcinkiewicz in Boston said she was unable to specify the nature of the alleged threat, but confirmed that the FBI was participating in an investigation in Bangor.

Ms. Marcinkiewicz said the plane was diverted to Bangor because it is the northernmost U.S. major airport. She said the plane carrying 188 passengers landed at 12:45 p.m. yesterday.

A TSA spokesman said that "given the current threat level, the agency, in conjunction with other federal authorities, took prudent action to ensure the security of passengers and crew." The spokesman said TSA canines searched the plane.

Also yesterday, a Charlotte, N.C.-bound U.S. Airways jet that had taken off from Phoenix made a forced landing in Oklahoma City after a federal air marshal reportedly subdued an unruly passenger. Authorities declined to give details pending a probe.

After the crew of Continental Airlines Flight 2258 discovered a missing panel in the lavatory, the plane, bound for Bakersfield, Calif., from Corpus Christi, Texas, was diverted to El Paso, Texas, according to the Transportation Security Administration. The plane, carrying 50 passengers, was held for about four hours before officials determined there was no danger.

"The passengers were interviewed, and the aircraft was thoroughly inspected with all the tools at our disposal, including canine teams," said Pat Abeln, director of aviation at El Paso International Airport. "At the end of the day, this was a precautionary event that turned out to be a nonevent."

There were three other incidents yesterday:

Authorities in Hartford, Conn., boarded U.S. Airways Flight 554 from Philadelphia yesterday morning after a passenger found a utility knife on a vacant seat. No arrests were made, and no threats issued, state police said. State police and the FBI were investigating whether the knife had been left on board by a worker or if a passenger had brought it aboard.

At Chicago's O'Hare airport, a flight attendant aboard United Flight 686 overheard a minor say he had a bomb, and alerted the pilot, who taxied to a secure part of the airport. The minor's mother and the minor were removed from the plane, and it was searched, an FBI official said. After bomb-sniffing dogs found no explosives, the flight, which was on a layover between Portland, Ore., and New York's LaGuardia, was allowed to continue.

In Ireland, an Aer Lingus plane from New York was evacuated at Shannon Airport after police received a call yesterday claiming "some sort of device" was on board. Police found nothing suspicious, Aer Lingus officials said yesterday, and the plane returned to service.

Aviation security has increased dramatically since British intelligence services announced Aug. 10 that they had broken up a plan to destroy trans-Atlantic airliners with liquid explosives. U.S. transportation officials responded by introducing strict new rules pertaining to carry-on objects. Liquids such as water bottles were banned, along with deodorant, lip gloss, mascara and other cosmetics. Products containing gel, such as shoe liners and in some cases, brassieres, also were prohibited.

Corey Caldwell, a spokeswoman for the Association of Flight Attendants-CWA, said yesterday that the ramped-up precautions were "long overdue," and that there was nothing excessive about the mood in the skies.

"The U.S. aviation system depends on layered security -- different levels of security," she said. "The more that we can put in place to ensure the safety inside the aircraft cabin, the safer our aviation system will be."

Ann Davis, a TSA spokeswoman in Boston, acknowledged that the elevated security measures have raised the anxiety and inconvenience level of air travel.

"I think the elevated threat level over the last few weeks has reminded travelers that the threat to aviation is still very real," she said. "We continue to emphasize the importance of coming to the airport prepared for screening and educating oneself on the restrictions to ensure that the inconveniences are minimal. But any time we have actionable information, we need to take every precaution to ensure the safety of the travelers despite the inconvenience that it might cause."

But Mr. Laird, the security consultant, said aviation officials often overreact following real or perceived threats. "This is common following an event. This reoccurs again and again," he said. "And every time it turns out to be a nonthreat, so to speak, I think that in a sense the terrorists can sit back and sort of chuckle, and say, 'We've really put them into a spin.' "