HOUSTON, Texas – A college student’s checked luggage on a Continental Airlines flight from Argentina contained traces of dynamite, authorities said, in one of six security incidents yesterday involving US flights.

Federal authorities were investigating why the student, who got off the Continental plane in Houston before it continued to Newark, NJ, had the explosive residue, FBI spokeswoman Shauna Dunlap said.

Houston Fire Department Assistant Chief Omero Longoria said the man told authorities he works in mining and often handles explosives. Longoria said federal officials were investigating whether the explanation was true.

In other incidents, a utility knife was found on a vacant passenger seat of a US Airways flight travelling from Philadelphia to Bradley International Airport in Connecticut, state police said.

US Airways jet was diverted to Oklahoma City after a federal air marshal reportedly subdued a passenger who was involved in an incident with a flight attendant, officials said.

An American Airlines flight from England to Chicago was forced to land in Bangor, Maine, for security reasons.

A Continental Airlines Flight for Bakersfield, Texas, was diverted to EL Paso after the crew discovered a missing panel in the lavatory, said Amy von Walter, a spokeswoman for the Transportation Security Administration.

An Aer Lingus flight from New York to Dublin was evacuated yesterday morning during a scheduled stopover in western Ireland following a bomb threat that turned out to be unfounded, officials said.

In Houston, the dynamite residue was found during a luggage search in a federal inspection station at Bush Intercontinental Airport shortly after Flight 52 landed at about 6:00 am Marlene McClinton, spokeswoman for the Houston Airport System, said a bomb-sniffing dog “had a hit” on explosive residue during a further search.

She said Customs and Border Patrol and the FBI shut down the customs area and began questioning the passenger who had the luggage.

Dunlap confirmed that the explosive was dynamite. Dunlap also said the man, one of 173 passengers on the flight, was from Connecticut and attends Lafayette College in Easton, Pennsylvania. After landing at Newark Liberty International, the plane was kept from the terminal as a precaution, authorities said.

In Connecticut, authorities said they received an emergency call at about 8:25 am reporting that a passenger on US Airways Flight 554 had found the knife and reported it to a flight attendant. When the plane arrived at Bradley, state troopers boarded the aircraft, seized the knife as evidence and interviewed passengers.