The Federal Aviation Administration has ordered a special inspection of 105 jet engines that slipped through a Miami maintenance station with unrepaired cracks in a critical component.

In a telegraphic emergency order, the aviation-safety regulator ordered a series of inspections and repairs, depending on the length of the cracks. All are in combustor cans of Pratt & Whitney JT8D engines. Air and fuel are ignited in the cans, nine of which surround the engine's center section.

The engine is the most widely used in civil aviation and is standard on about two-thirds of U.S. airplanes, including all McDonnell Douglas DC9s and Boeing 727s. A combustor can that failed explosively apparently started the fire on a British Airtours Boeing 737 on takeoff from Manchester, England, last August. Fifty-five of 135 on board were killed.

The engines involved belong to 27 different customers of the Miami repair station, Aerothrust Corp., an FAA spokesman said. About 30 of the engines belong to the U.S. military, and at least one is on an FAA plane, the spokesman said. Most of the engines belong to private operators and a few to small airlines, the FAA said.

J. Larry Helms, vice president of marketing for Aerothrust, said in a telephone interview that the combustor cans on engines in question were sent to a subcontractor for examination, including X-rays to detect cracks.

When the engines and X-rays were returned, Helms said, there "was a slip-up on one individual's part . . . . One inspector thought he was supposed to ingore the X-rays."

Helms said that, in mid-December, Aerothrust revised some shop procedures. "When our inspector reviewed this, he realized it had a process in it that he wasn't doing, and he brought it to management's attention," Helms said.

Records were reviewed to determine which customers were affected and "we went to the FAA on Jan. 6," Helms said.

FAA officials said they are investigating. Additionally, they moved Aerothrust to the top of the list of jet-engine repair stations nationwide that are receiving intensive FAA inspections.

"I met with the FAA this afternoon, and they are going to start at 7 a.m. tomorrow," Helms said. He said his company works exclusively on JT8D engines.