The Federal Aviation Administration Saturday issued an emergency order restricting Boeing 737-100 and 737-200 planes with more than 55,000 landings to flights of no higher than 23,000 feet until they are inspected.

FAA spokesman Fred Ferrar said the order was issued because of the accident Thursday involving Aloha Airlines Flight 243 a Boeing 737-200 which was flying at 24,000 feet when a 20-foot chunk of fuselage behind the cockpit was peeled back. One flight stewardess was killed in the accident.Ferrar said the Emergency Airworthiness Directive issued by FAA director T. Allan McArtor would affect about 66 planes flown by three airlines Aloha, Piedmont and American Airlines although the airlines said only about 36 planes would be covered.

The airlines had 12 hours to comply, but American said it never uses its 737s above 23,000 feet, Piedmont said it hardly ever does and Aloha had already grounded all its 737s covered by the order.

The FAA order affects "all 737-100 and 737-200 aircraft that have had more than 55,000 landings," said Ferrar.

"Within 12 hours after receipt of the order, these aircraft will have to be restricted to no more than 23,000 feet altitude," and the entire upper fuselage is to be inspected "within the next 500 landings" for skin cracking, corrosion or delamination. The altitude restrictions will be lifted if the planes pass inspection, Ferrar said.

The order was sent by telegram Saturday morning, Ferrar said.

Ferrar said the altitude of 23,000 feet was selected because 24,000 feet is the altitude where the difference in pressure inside and outside the plane makes it the most likely altitude for structural failure.

The order was issued in Washington and at the FAA regional office in Seattle, which is specifically responsible for certifying all commercial passenger aircraft operated in the United States.

"This applies to all Boeing 737-100 and

-200 series airplanes which have accumulated more than 55,000 landings, certified in any category," said Dick Meyer, a spokesman for the Seattle office.

The Aloha Airlines jet that was ripped open on a flight from Hilo on the island of Hawaii to Honolulu, forcing an emergency landing in Maui, was a heavily used older model Boeing 737-200 that federal officials had warned could develop dangerous cracks in the fuselage.

NTSB investigators said Friday night their probe into the incident will focus primarily on possible defects in the plane's structure.

Aloha grounded three similar Boeing 737s Friday after the airline learned Boeing planned to order inspections of heavily flown planes of the same model.

The Boeing directive requires inspection of 737-200 aircraft with more than 55,000 takeoffs and landings since manufacture, an Aloha statement said.

Piedmont flies about 62 737-200s, but only 17 have 55,000 landings and will have to be inspected, said spokesman Bill Kress in Winston-Salem, N.C.

"We are currently completing inspections on two or three aircraft and we will continue looking at them through the weekend. It's regular maintenance anyhow. . . . We check them every 3,000 miles," he said.