In this story: Alarms, but no voices Pressurization limits and reactions Flight's ghostly path More investigative work RELATED STORIES, SITES

November 23, 1999
Web posted at: 10:49 p.m. EST (0349 GMT)

WASHINGTON (CNN) -- Federal investigators said Tuesday the cockpit voice recorder recovered from the wreckage of golfer Payne Stewart's Learjet 35 includes the sounds of a low-pressure alarm -- consistent with suspicions that the plane lost cabin pressure during its flight.

Stewart, 42, was one of the world's most recognizable golfers because of his trademark knickerbockers.

	IMAGE GALLERY:
Payne Stewart, golf champion, husband and father

The plane carrying Stewart and five others crashed October 25 near Aberdeen, South Dakota, after traveling 1,500 miles, most of it while the pilot, co-pilot and passengers were apparently unconscious or dead.

The aircraft crashed with such force it burrowed into the ground, opening a hole 40 feet wide and more than 10 feet deep.

The badly damaged cockpit voice recorder was sent to Washington state so its manufacturer could assess its contents.

Alarms, but no voices

National Transportation Safety Board investigators have said no voices are on the recorder, which only records the last 30 minutes of activity.

On Tuesday, investigators reported that the recorder includes "sounds consistent with various alarms," including a low-pressure alarm.

The NTSB did not indicate what caused the apparent loss of pressure, but said parts of the pressurization and oxygen systems have been taken to several manufacturers for examination.

Pressurization limits and reactions

The human body has a limited ability to function above 10,000 feet because there is less oxygen in the air and there is less pressure to force that oxygen through the lungs and into the bloodstream.

Airplanes are pressurized so that the atmospheric pressure inside never feels higher than about 8,000 feet even if the aircraft is flying much higher.

Federal Aviation Administration officials said the plane climbed as high as 51,000 feet during its wayward flight across the nation's heartland.

Dave Franson, a spokesman for Learjet based in Wichita, Kansas, said an alarm in the Learjet 35 cabin automatically sounds if cabin pressure reaches the equivalent of an altitude of 10,000 feet.

That alarm is not a soft beeping noise, but a loud horn to alert the crew to the problem, he said.

When the alarm sounds, pilots correct the problem by manually activating an emergency pressurization system, donning their oxygen masks and initiating a descent, Franson said.

Flight's ghostly path

Stewart's flight originated in Sanford, Florida, and was headed for Texas, where Stewart was scheduled to participate in a golf tournament.

Air traffic controllers lost contact with the plane after clearing it to ascend to 39,000 feet near Gainesville, Florida.

U.S. Air Force fighter pilots who intercepted the plane and followed it to Missouri were unable to contact its pilots. Pilots of those fighters have told investigators that the windshield of the Learjet was frosted over and the passengers were "non-responsive."

The jet continued on its ghostly flight, apparently controlled by autopilot, before running out of fuel and crashing in a South Dakota field with over 100 times the force of gravity.

More investigative work

NTSB investigators said various fragments of the aircraft, including parts of the pressurization and oxygen systems, have been taken to several manufacturers to be examined.

The airplane's engines, which were severely damaged in the crash, were also being inspected, the NTSB said.

Investigators have completed their work at the accident site and have stored the bulk of the wreckage at Aberdeen Regional Airport.

They are interviewing passengers who took earlier flights on the plane as well as pilots who had previously flown the aircraft.

Also, they are reviewing the airplane's records and service history and finalizing radar tracking information that detail the plane's performance during the flight.

Correspondent Carl Rochelle, Producer Mike Ahlers and Reuters contributed to this report.

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