By Stephen Thorne / The Canadian Press

Seattle - The world's top aviation regulator has ordered emergency inspections of MD-11 jets like the one that crashed off Nova Scotia after damaged wiring and charred insulation was found aboard a World Airways plane.

The U.S. Federal Aviation Administration ordered operators of 45 U.S.-registered jets to check for installation of a wire harness support bracket and clamp in a cargo compartment aboard the tri-engined jets.

"A missing bracket and clamp could cause a wire bundle to contact the insulation blanket and rub against the fuselage frame, producing a possible fire source," said a statement released Tuesday by the regulator.

"This emergency airworthiness directive does not appear to be related to the Swissair accident. However, it is prompted by information from the agency's continuous post-accident review of the ... MD-11 fleet."

Chafing and wear of wire leading to electrical arcing, or lightning-like jumps from wire to wire, is believed to have been a factor in September's crash of Swissair Flight 111. All 229 people aboard the New York-Geneva flight were killed after the pilot reported cockpit smoke.

Subsequent inspections of other MD-11s found some had cracked and chafed wiring around forward cabin doors and the wall separating the cockpit from the forward galley.

As a result, the FAA issued several wiring-related airworthiness directives affecting the entire U.S.-registered fleet of 89 MD-11s.

The directives are the agency's most drastic action short of grounding a fleet and are routinely followed by other regulators worldwide. There are 186 MD-11s in service; none in Canada.

The latest directive affects American Airlines, Delta Airlines, World Airways, Federal Express Corp., and Boeing Co. It warns that a wire aboard a World Airways plane was "cut and three other wires were missing insulation.

"In addition, Frame 1681 had signs of arcing damage."

It said the insulation blanket was burned and a hole was found in the insulation blanket where the wiring harness was chafing against the frame.

The bracket and clamp were inadvertently not installed by Boeing, said the order.

Operators were required to perform inspections and repairs within five days and report results to the FAA within 10 days, said the order, banned from publication until now.

The directive was aimed at MD-11s with 72-inch cargo doors and was not restricted to aircraft, like Flight 111, where wiring is insulated with vulnerable aromatic polyimide tape known as Kapton. Boeing stopped using Kapton in new planes shortly after the Swissair jet went into service.

The Flight 111 aircraft is believed to have had a 104-inch cargo door, said Lori Gunter, a California-based spokesman for the manufacturer.

Most airlines have already complied with the order, said Gunter, who was checking daily service reports.

"It is not specific to Kapton wiring," she said. "It has to do with the way it was installed. I really think in this case it's strictly an installation problem."

Last week, a Korean Air Lines MD-11 cargo jet crashed in China, killing up to seven. It was the third MD-11 hull lost in a crash since the first McDonnell Douglas aircraft went into service in 1990.

The metalized mylar blanket insulation used in the fuselage to dull sound and protect against cold has also been under scrutiny for its flammability. The blankets have been factors in several fires and their potential role in the Swissair crash is under investigation.

The FAA is researching new standards and developing a new flammability test for the material, while several companies are making a replacement product.

MD-11s have been subject to about 20 wiring-related airworthiness directives since 1992.

According to an industry newsletter, Aero Safety and Maintenance, the FAA expects to soon release several more directives involving MD-11 wiring.

The orders will cover the cockpit overhead switch panel, the aft main avionics rack and the galley load control unit, an unidentified FAA spokesman told the publication.