A Federal Aviation Administration specialist testified today that employees of the manufacturer, and not those of the FAA, initially approved test results that declared safe the engine support pylon on the McDonnell Douglas DC10.

Those tests, called fail-safe analyses were conducted during the late 1960's and early 1970's when Douglas was seeking FAA certification for the DC10. The testimony came at the opening of the second week of National Transportation Safety Board hearings on the crash of an American Airlines DC10 here May 25 that killed 273 people.

Douglas Sharman, an aerospace engineer with the FAA's Los Angeles office, testified that the results of the fail-safe analysis on the DC10's engine pylon were approved by a "designated engineering representative" and that "I don't recall personally reviewing it..." Sharman said he has been project engineer for the DC10 since the plane's time on the drawing boards.

The Chicago crash occurred when the pylon supporting the engine under the left wing dropped away during takeoff. Vital flight controls and crew warning devices were disabled in the process.

Designated engineering representatives (DERs) are common throughout the aircraft manufacturing industry. They work for the manufacturers but act on behalf of the FAA to approve designs, witness tests and study the results of analyses. The question of whether the DER system presents an irreconcilable conflict of interest within U.S. aviation is an old one; it has been revived as a result of the DC10 crash.

During testimony, Sharman said that, in his view, the aft bulkhead in the pylon - the part that broke and led to the Chicago crash - "meets the fail-safe requirements." Investigators have found that the pylon bulkhead was damaged during maintenance. Sharman was asked if such maintenance trouble should have been anticipated. In his reply, he invoked aviation's favorite axion - Murphy's law.

"When you get to Murphy-type incidents - those are the kinds of things it is not reasonalbe to assume," Sharman said. Murphy's law holds that if anything can go wrong, it will, at the worst possible time. Aviation engineers have talked endlessly about the necessity to "Murphy-proof" airplanes and systems. "It's hard to outguess Murphy," Sharman said.

In other testimony today, McDonnell Douglas took three steps to improve its position:

The company released a statement from C. W. O'Connell, a Douglas employee, to the effect that he had orally advised an American Airlines official that Douglas would not encourage the maintenance procedure now blamed for cracking the pylon bulkhead.

William Gross, the leader of the Douglas team here, offered to provide a "qualified witness' to rebut the contention of W. C. Walton Jr. that wind gust stresses on the DC10 pylon might not be adequately understood. Walton, chief dynamicist with the National Aeronautics and Space Administration, made the statement in a letter released last week.

Dale Warren, a top Douglas engineer, said that the installation of a shim by Douglas during manufacture of the pylon that broke on the crashed plane was of little significance. American Airlines has contended that the shim lengthened the crack in the pylon bulkhead to a critical state.