McDonnell Douglas's new DC9 Super 80 has made its Washington debut -- and has delivered on the company's promise that it would be much quieter than other planes in its class.

"American technology can be responsive to the environment," Charles M. Forsyth, executive vice president of Douglas Aircraft Co., a division of McDonnell Douglas, told those invited to look on as the plane flew over and then landed at Washington National Airport.

"It's not only 25 percent more fuel-efficient than its contemporaries, it's also about half as loud. You've just seen that demonstrated," said Forsyth.

Indeed, guests who had been taken to a dock at the Washington Sailing Marina to watch -- and hear -- the fly-over, found the Super 80 much qieter than the Boeing 727s and small private business jets that preceded and followed it on the flight path.

The Super 80 is the sixth and largest version of the popular twin-engine DC9. It is a full 44 feet longer than the original, and is powered by quieter, more-efficient engines. It has a higher-capacity fuselage, larger and more efficient wings, and an advanced digital flight control system.

The plane is powered by two Pratt & Whitney Aircraft JT8D-209 engines that provide more thrust than earlier versions but turn less fuel and cut noise emissions.

The Super 80 will meet current noise abatement requirements set by the Federal Aviation Administration as well as the more stringent international standards for new aircraft designs, Douglas and government officials said at the demonstration.

The latest version can carry up to 172 passengers compared with a seating capacity of up to 80 passengers on the original DC9. Seating on the plane is five across, three on one side of the aisle and two on the other.

Test flights, with FAA officials on board, are designed to demonstrate the plane's ability to use a two-person crew. Part of the test simulates emergencies that would render one of the pilots incapacitated and require the other to land the plane alone.

On the way back from here to the company's headquarters in California, the operators of the plane sought bad weather to show the FAA inspector on board how the plane and its engines function in "natural icing" encounters, according to a Douglas official.

Douglas representatives expressed optimism that a recent accident involving one of its test planes won't seriously affect certification or scheduled deliveries of the plane.

One of the planes was damaged in a "hard landing" during performance tests in California for the FAA. The tailwing was severed and the fuselage buckled when the pilot failed to steady the plane before touchdown, one official said.

None of the five crew members or two FAA officials aboard was injured seriously.