BILLINGS, Mont. (AP) _ A Northwest Airlines flight traveling from Minneapolis to Bozeman Wednesday was diverted to Billings because of a mechanical problem.

An airline spokesman said the hydraulic problem was not linked to the strike by Northwest mechanics and maintenance workers that began Saturday.

The Airbus A320 with 136 passengers aboard landed at Billings Logan International Airport during the afternoon and passengers used portable stairs to exit the plane. There were no injuries.

``We heard this flapping noise. The captain came on the intercom and said we were having hydraulic problems,'' said passenger Kathee McCafferty of Traverse City, Mich.

She said passengers began hearing unusual noises about a half-hour before the plane touched down.

Nonunion replacement workers have been providing aircraft maintenance since 4,430 mechanics, cleaners and other members of the Aircraft Mechanics Fraternal Association went on strike over $176 million in pay and benefit cuts that the airline had demanded.

Kurt Ebenhoch, a Northwest Airlines spokesman from Minneapolis, described the problem on Flight 1271 as a ``hydraulic issue,'' but declined to be more specific. He said such problems crop up periodically, irrespective of any labor disputes.

Ebenhoch said the plane remained in Billings Wednesday evening and would be returned to Northwest's fleet as soon as possible. He said passengers who weren't able to arrange their own transportation were taken to Bozeman in a bus.

Also Wednesday, a Northwest plane at Baltimore-Washington International Airport had its tires deflated, forcing passengers to take other flights, the airline said.

Two landing gear tires on a 757/200 were found to be deflated during a preflight inspection, according to Todd Morgano, a spokesman for Northwest. No other damage was found, he said.

Passengers scheduled to take the flight to Minneapolis were put on other flights.

Morgano said the airline was cooperating with federal officials in investigating the incident.