Probable Cause

It took 28 seconds for USAir Flight 427 to plummet from the sky. It took the National Transportation Safety Board five years to figure out why.

Air & Space Magazine

(Continued from page 6)

While the Boeing-FAA meeting was going on in Renton, Phillips and Tom Haueter, the lead NTSB investigator, were 2,000 miles away in Pittsburgh, unaware of the developments. They had returned to the Holiday Inn near the Pittsburgh airport to meet with all the parties. Haueter and each of his group leaders gave updates on the investigation. Phillips reviewed the results of the thermal shock tests (without knowing of Boeing’s finding) and discussed what work still needed to be done. Rick Howes, the Boeing coordinator for the investigation, sat through the all-day meeting without saying a word about the company’s big discovery.

When the meeting broke up, Haueter, Phillips, and Tom Jacky, the NTSB performance chairman, took a flight back to Washington. As they got off the plane at National Airport and walked toward the subway station, Haueter’s beeper went off. The NTSB had a new pager system that could transmit words as well as phone numbers.

Haueter glanced down at it. “major finding rel to pit / defect found on servo valve,” the pager said.

“This is a joke,” he said. “This isn’t real. Some jerk has figured out our paging system.” They went their separate ways and headed home.

The message had come from Ron Schleede, Haueter’s boss, who had been working late in the NTSB office when McGrew and John Purvis, the head of Boeing’s accident investigations, called to tell him about the finding. Schleede transmitted the message to Haueter and then walked downstairs to the bar at the L ’Enfant Plaza Hotel, where NTSB chairman Jim Hall was having a drink.

“Jim,” Schleede said, “I think we’ve got it.”

The next day, the FAA briefed Haueter, Phillips, and other NTSB officials about the finding. Haueter realized that it was a major piece of his puzzle.

“This isn’t the way I thought it would end,” he told Phillips as they walked back after the meeting. “I expected it was going to be a fight all the way to the end, putting all these little pieces together, with people saying we wouldn’t have enough evidence. And all of a sudden here is something no one expected.”

That day, Boeing sent a telex to every airline in the world that flew 737s:

Alert Alert Alert Alert Alert Alert Alert Alert
Boeing Alert Service Bulletin 737-27A1202
November 1, 1996.
The dual servo valve is designed to overcome the effects of a jammed primary or secondary slide. Although there has never been a report of a secondary slide jam, tests just completed at Boeing have shown that, under certain conditions, some jams of the secondary slide can result in anomalous rudder motion.

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