FAA Says Learjets Had Valve Failures

Previous problems with valves like the one that may have failed, causing catastrophic decompression aboard the executive jet carrying Payne Stewart, were reported Tuesday as federal experts began their investigation of the crash that killed the pro golfer and five others.

While the cause of Monday’s crash probably won’t be determined officially for months, National Transportation Safety Board investigators are focusing on the possibility that decompression disabled all six people aboard the Learjet 35 after it took off from Orlando, Fla.

The executive jet, probably on autopilot, flew 1,400 miles at altitudes of more than 44,000 feet before apparently running out of fuel. Air Force pilots, who scrambled to escort the wayward plane after air traffic controllers were unable to make radio contact, watched in horror as it spiraled downward before crashing nose-first into pastureland about a mile south of this tiny rural hamlet in northeast South Dakota.

Killed, in addition to Stewart, were the plane’s pilots, Michael Kling and Stephanie Bellegarrigue; Stewart’s agents, Robert Fraley and Van Ardan; and golf course designer Bruce Borland.

Officials say all six probably succumbed to high-altitude asphyxiation long before the plane struck the ground.

Aviation safety experts have suggested several scenarios that might have caused decompression, one of them involving a failure of the Learjet’s outflow valve, a regulator designed to keep air pressure in the plane at the desired level--usually about the same as in an unpressurized plane at an altitude of about 5,000 feet.

The Federal Aviation Administration said Tuesday that in 1994 pilots reported problems with the seals on some outflow valves on Learjets, including one failure that caused the nonemergency decompression of one plane.

The FAA issued an airworthiness directive in 1995 mandating repairs on the valves within 18 months and limiting the altitude of Learjets to 41,000 feet until the repairs had been completed.

These repairs apparently were made on the plane carrying Stewart, and officials said there were no reports of serious maintenance problems with the jet.

The officials said another possible scenario that could lead to decompression would involve the failure of an inside pressure bulkhead.

The Air Force pilots said they saw no damage on the Learjet, but the failure of an interior bulkhead or an outflow valve might not be visible from a plane flying alongside.

A third possible scenario involves the failure of the cockpit crew to activate the Learjet’s main pressurization system before taking off. When that happened on a Learjet in 1988, the two pilots--the only ones on board--were incapacitated shortly after taking off from Memphis, Tenn., and the plane flew on its own to Mexico before crashing. Both pilots died.

Noting that there still are several possibilities, NTSB Vice Chairman Robert Francis said Tuesday night that investigators “were having trouble figuring out how or if” the airworthiness directive about outflow valves applies to the current investigation.

But sources close to the investigation said the outflow valve from Stewart’s jet was one of the key pieces of wreckage NTSB investigators were seeking Tuesday as they began to study the impact crater--10 feet deep, 40 feet long and 30 feet wide--gouged in the earth of the gently rolling pastureland.

The main job Tuesday was the grim task of recovering the fragmented human remains, scattered throughout the debris-filled crater and around its perimeter.

Francis, who is overseeing the investigation, said NTSB experts--assisted by local emergency personnel--had to work slowly and meticulously taking care not to destroy evidence.

Tuesday’s efforts were largely confined to the area around the crater. Francis said heavy equipment probably will be brought in today to begin excavating the crater.

Yet to be recovered, officials say, is the plane’s “black box” cockpit voice recorder. Even if it is recovered intact, the device may be of limited value in this investigation because it retains the cockpit sounds of only the last 30 minutes of flight, erasing earlier recordings.

It is presumed that all those aboard the Learjet lost consciousness about 20 minutes into the flight, which continued on for more than three hours. Air Force pilots escorting the executive jet said its windows were frosted by the apparent decompression, and they could not see inside.

Francis said a videotape of the wayward Learjet taken by one of the Air Force pilots was shot through the instrument readings projected on the pilot’s windshield, so the quality probably was not good enough to be very helpful.

Questions have arisen as to whether the Learjet pilots reacted swiftly to a serious situation before becoming incapacitated. Figures provided by Francis show that neither had much experience with a Learjet.

Kling, the pilot in command, had more than 4,000 hours of total flight time but only 37 hours of it in a Learjet. Bellegarrigue had about 2,000 hours total time, only 250 in a Learjet.

Kevin Monmaney, an experienced Learjet pilot who has given pilots training tests in the air, in simulators and in classrooms for the FAA, said Tuesday that a pressure problem normally sets off multiple warnings.

First, the pilots would see an amber warning light in the cockpit when the pressure began to change. When cabin pressure reached the equivalent of 10,000 feet, a horn would sound and the amber light would turn red. When the pressure hit 14,000 feet, the oxygen masks would automatically deploy. They do so even if the cabin has lost power.

“If you don’t [put the masks on] in seconds, it’s over,” Monmaney said.

He noted, however, that the many backup warning systems can sometimes overwhelm and confuse pilots to the point where they are unable to identify the main problem and take immediate action.

“It may sound strange,” he said, “but I’ve seen pilots in a simulator not know they have engine failure.”

“In a bad situation, where the cabin pressure was going fast, you’d have cabin lights, mask lights, all kinds of bongs and horns going off. If they even discussed it for 15 seconds, that could be all it takes [until they black out]. The decision has to be taken immediately.”

Times staff writer Stephanie Simon in St. Louis contributed to this story.