John Brizendine, president of the company that builds DC10 jumbo jets, told Congress yesterday that properly maintained, properly inspected DC10s are safe airplanes and that the grounded U.S. fleet should be permitted to return to service.

However, Brizendine and other officials of the Douglas Aircraft Co. division of McDonnell Douglas said they did not know why an engine and its support pylon came off the left wing of the DC10 that crashed in Chicago May 25 and killed 273 people.

Rep. Allen E. Ertel (D-Pa) said, "I'm amazed at your conclusion [that the DC10s should be returned to service]. It doesn't make sense."

Brizendine said the crashed DC10 was carrying an "injured" part in the pylon assembly - a fact investigators have confirmed. "I know a healthy part will not fail," Brizendine said.

"We also know," Ertel shot back, "that if one of the healthy parts fails, the fail-safe system does not work." Brizendine and his colleagues had spent hours of testimony before two subcommittees of the House Public Works and Transportation Committee explaining that if one part of the DC10 engine pylon assembly failed, another was supposed to take up the slack.

At one point Brizendine said, "The fail-safe requirement says that another part must carry the load. It doesn't say for how long."

Representatives of airlines that own DC10s and the pilots who want to fly them were dismayed by the McDonnell Douglas performance in the second day of hearings by the committee. Several agreed, after being granted anonymity, that it would be harder than ever to get the DC10s off the ground as a result of the hearing.

Federal Aviation Administration chief Langhorne M. Bond grounded the three-engine wide-bodied jet June 6 after a series of inspections discovered cracks in the aft pylon bulkhead - one of the parts that is known to have failed in the Chicago crash.

Bond said maintenance procedures of the various airlines and a "possible design problem" forced him to take the extraordinary action.

Brizendine said tests and inspections conducted on DC10s around the world have "not revealed to us any reason to doubt the DC10s design or its continued ability to perform."

The hearing yesterday also produced evidence supporting American Airlines' position that its maintenance procedure on the DC10 engine and pylon was at least tacitly approved by McDonnell Douglas. That procedure has been blamed by the National Transportation Safety Board for having caused a 10 1/2-inch crack in a flange of the aft pylon bulkhead in the plance that crashed, American Airlines Flight 191.

A document Brizendine supplied the committee at Ertel's request showed that in 1977 American Airlines asked McDonnell Douglas for specific technical data to assist American in dropping the engine and pylon "as a single unit package."

An accompanying document shows that McDonnell Douglas provided the data without comment on the proposed procedure.

Brizendine testified that McDonnell Douglas had recommended against the procedure, but had done so orally, not in writing. The McDonnell Douglas maintenance manual recommends separate removal and replacement of the engine and pylon.

The safety board has found that when the engine and pylon are removed and replaced as a single unit, damage to the pylon flange is more likely to occur. The FAA has outlawed the single-unit procedure since the crash.

After Bond grounded the DC10s, McDonnell Douglas issued a statement saying that cracks had been found only in pylons that were removed and replaced "contrary to the recommended procedures."

McDonnell Douglas first knew that damage to the pylon could occur, according to testimony, when Continental Airlines cracked a pylon, informed McDonnell Douglas and asked for advice on repairing it.

McDonnell Douglas reported that incident to other DC10 operators in an "operational occurrences report" dated Jan. 5. A copy of the report, made available to the committee yesterday, shows that the pylon damage was the last "operational occurrence" listed in two pages of such events. It followed a complaint from a flight attendant that she had suffered a fractured big toe on her right foot when it was caught under a cart in the DC10 cabin.

"I don't know that we attached a great deal of significance at the time to what the method of hndling the engine and pylon was," Brizendine said. CAPTION: Picture, Douglas Aircraft President John Brizendine: "I know a healthy part will not fail." by James K. W. Atherton - The Washington Post