The Federal Aviation Administration temporarily grounded all but two of Arrow Air's planes yesterday after inspectors discovered "the use of unapproved spare parts in 10 airplanes."

The Air Force quickly followed suit, saying it has "curtailed" Arrow Air flights "until such time as the result of the ongoing" FAA inspections "are known and reviewed." Col. Terry Y. Arnold, an Air Force spokesman, said the Air Force will fly no passengers on Arrow until the FAA inspection is completed and reviewed, although cargo flights could resume as early as next week.

An Arrow charter crashed in Gander, Newfoundland, in December, killing 248 U.S. soldiers and eight crewmembers. There is no indication whether unapproved parts were involved, but little in the way of formal findings has been released by the Canadian investigators, and the cause of the crash is unknown.

That crash has brought the Miami-based airline its third intensive FAA inspection in less than two years, and there have been demands from Capitol Hill that the Air Force, at a minimum, stop using the airline.

Arrow Air spokesman Robin Mattel called the FAA action "totally incomprehensible, because all airlines, large and small, operating outside the United States, use these same parts." He said the FAA had "previously given us permission to use these parts, which were certified by an FAA-approved repair station in Europe."

Arrow, Mattel said, "voluntarily agreed" to change the parts as quickly as possible. "We plan to have the parts changed and all planes flying by early next week." He said Arrow had to cancel one scheduled flight yesterday, from its hub airport at San Juan to New York, but by nightfall had three planes back in the air.

Arrow holds $20.6 million in cargo and passenger contracts from the Air Force. From yesterday through Tuesday, Arnold said, six scheduled contract Arrow flights were affected. "Four of these flights have been replaced by military aircraft and two others by commercial contract carrier," he said.

Mattel said that Arrow has 12 airplanes -- 10 McDonnell Douglas DC8s of the type that crashed in Gander, and two Boeing 727s. Under the FAA order, the planes can be returned to service as soon as unapproved parts are replaced.

"Arrow has been directed to remove the parts before any further passenger or cargo flights," FAA spokesman Stephen Hayes said. He said 68 parts in 10 airplanes were involved, including valves, pumps and actuators. Such parts appear most frequently in fuel or hydraulic systems, which provide "power steering" to flight controls and raise and lower the landing gear.

FAA regulations require that parts purchased abroad meet FAA standards when used in the United States. Hays said the FAA "has initiated an enforcement action against Arrow Air." Last June, Arrow paid $34,000 in civil penalties to settle charges of safety violations the FAA developed during special investigations.

The parts came on the airplanes when they were purchased from foreign airlines, or as spares delivered with the airplanes. Arrow's fleet consists of older aircraft. The plane that crashed in Gander, for example, was delivered new in 1969 to Eastern Air Lines, then found its way to France and two other airlines before returning to the U.S. register with Arrow.

Hayes said use of the parts "does not necessarily reduce safety," but that "the FAA cannot be immediately assured that these parts meet FAA certification requirements."

A House Armed Services subcommittee passed a nonbinding resolution last week urging a halt to all Arrow Air contracts until all pending investigations are concluded. That came in partial reaction to a new $7.6 million add-on to a $13 million contract Arrow received last September from the Air Force for chartered flights.