*

Plane could help pave way for faster commercial air travel

*

Aircraft built to break sound barrier with sonic 'thump'

*

Designed to cruise at Mach 1.4 at altitude of 55,000 feet

*

First test flight appears to have been subsonic

(Adds details about first flight, aim of X-59 project,

paragraphs 1-11; transportation secretary comment paragraph 16)

By David Swanson and Steve Gorman

PALMDALE, California, Oct 28 (Reuters) - NASA's X-59

supersonic-but-quiet jet soared over the Southern California

desert on Tuesday in the first test flight of an experimental

aircraft designed to break the sound barrier with little noise,

paving the way for faster commercial air travel.

The sleek aircraft, built for NASA by aerospace contractor

Lockheed Martin ( LMT ), took off about an hour after sunrise from a

runway at Plant 42 of the company's Skunk Works facility in

Palmdale, about 60 miles (100 km) north of Los Angeles.

After a steep climb over sod fields just east of the runway,

the plane was seen banking to the north on a trajectory toward

Edwards Air Force Base, where it landed safely about an hour

later near NASA's Armstrong Flight Research Center. It was

accompanied by a NASA chase plane.

The plane's unique shape is designed to greatly reduce the

explosive-like sonic boom normally produced when an aircraft

breaks the sound barrier, lowering the volume to a muffled

"sonic thump" no louder than slamming a car door.

Perfection of such low-decibel flight technology is aimed at

overcoming one of the primary obstacles to supersonic commercial

flight, long restricted over populated areas on land due to

noise concerns, according to Lockheed.

The single-engine X-59, measuring just under 100 feet

(30 meters) from nose to tail, flew at subsonic speeds, as was

expected for its initial test flight, reaching 230 mph (370

kph), according to Lockheed Martin ( LMT ). Its peak altitude during the

flight was 12,000 feet (3,660 meters).

About 200 aerospace workers and their families watched the

takeoff from a safe distance parked along a nearby highway.

"X-59 successfully completed its first flight this morning,"

Lockheed Martin ( LMT ) spokesperson Candis Roussel told Reuters in a

brief email statement, hailing it as a "significant aviation

milestone."

NASA's lead X-59 test pilot Nils Larson was at the controls

in the single-crew cockpit for the flight, Roussel said.

The X-59, a one-of-a-kind experimental aircraft, is built to

reach a cruising speed of 925 mph (1,490 kph), or Mach 1.4, at

an altitude of 55,000 feet (16,764 meters), more than twice as

high and nearly twice as fast as conventional airliners fly, the

company said.

Data derived from research with the X-59 will inform

development of new sound thresholds for supersonic flight over

land, the company said.

The supersonic Concorde aircraft began scheduled

transatlantic flights with British Airways and Air France in

1976. But the plane was retired in 2003 due to high operating

costs, limited seating and sluggish passenger numbers following

a fatal crash in July 2000 and the September 11 attacks in 2001.

In press materials posted online last month, NASA said the

X-59's first flight would be a "lower-altitude loop at about 240

mph (386 kph) to check system integration, kicking off a phase

of flight testing focused on verifying the aircraft's

airworthiness and safety."

During subsequent test flights, the X-59 will travel higher

and faster, eventually exceeding the speed of sound -

approximately 761 mph (1,225 kph) at sea level.

The California Manufacturers & Technology Association

earlier this month named the X-59 as 2025's "Coolest Thing Made

in California" in its annual statewide technology contest.

"This work sustains America's place as the leader in

aviation and has the potential to change the way the public

flies," U.S. Transportation Secretary Sean Duffy, who is also

acting NASA administrator, said in a statement.