The torture tests on the 747 valve were no different from hundreds of others performed in the Bendix lab that year. The technicians placed the valve in a tiny freezer and hooked up the hydraulic lines. Once the valve had cooled to sub-zero, they flipped a switch and heard the steady whine of the hydraulic pumps. They moved the valve back and forth, as if a pilot were stepping on the pedals. Then someone flipped another switch, and piping hot fluid shot inside. Usually the valve kept moving. But this one strained and then stuck for a few seconds.
It had failed the test.
When Vick heard about the results, he knew it was a setback but not a catastrophe. The valve was an amazingly tight device, with only a few millionths of an inch between each slide, so a very tiny design error could cause a jam. The Bendix engineers went back to their drawing boards and redesigned the tolerances. The new valve passed without problems.
Vick unpacked his suitcase in his hotel room and sat down at the desk with a legal pad. He had come to Washington for the first meeting of the “Greatest Minds in Hydraulics” to review Haueter and Phillips’s work. The goal of the panel was to look for new tests that the safety board should try. At sixty-seven, Vick was a quiet, serious man, a good choice for the group because he had designed dozens of valves and had been awarded twenty-five patents. He was quite familiar with the unique valve-within-a-valve used for the 737 rudder.
Sitting in his hotel room, he recalled the Bendix test thirty years earlier when hot fluid hit cold metal and the prototype valve stuck for a few seconds. That jam turned out to be no big deal—a redesign took care of the problem. But he wondered if the rudder valve on the USAir plane had stuck the same way. He sketched a brief outline of the test on a piece of paper and gave it to Phillips the next day.
“I think we should look at this,” Vick said. “It may be something.”
The NTSB had not done a thermal shock test on the 427 valve because there had been no comments on the cockpit tape about a hydraulic problem. If one of the pumps had broken, it would have triggered a warning light in the cockpit and the pilots would likely have mentioned it. But Phillips agreed to try the test. He was open to any suggestion.
The power control unit from the USAir crash would be frozen to 40 degrees below zero, similar to the outside air temperatures at 30,000 feet, and then it would be pumped with hot hydraulic fluid.
No one expected a breakthrough. The 737 valve had passed its own thermal shock test when it was certified in the 1960s. Besides, the temperature range was far more extreme than anything the PCU encountered in real life. Boeing officials viewed the test as a waste of time. McGrew said a 737 would encounter thermal shock conditions only if it flew to the moon.
On August 26, the Greatest Minds in Hydraulics and Phillips’s systems group gathered at Canyon Engineering, a tiny hydraulics company in an industrial park in Valencia, California. Cox thought the place looked more like a garage than a modern test facility. They had chosen Canyon because the chairman of the expert panel worked there, but the company did not have the sophisticated test equipment that Boeing and Parker did. Phillips brought the PCU in a sturdy navy blue chest, like a violinist carrying his prized Stradivarius. He took the 60-pound case to his hotel room each night to make sure that no one could tamper with the device.
At Canyon the PCU was placed in a big white Coleman cooler, the same kind you would take on a picnic. It looked like an amateur setup. Holes were cut in the cooler for pipes and tubes and then sealed with gray duct tape. When someone opened the cooler, frost formed on the PCU, making it look like a giant Popsicle. Cox and several others in the room said they were concerned that the temperatures were not controlled closely enough to produce legitimate results. But they forged ahead with the tests to see what would happen.
The group tested two PCUs—a new one straight from the factory and the one from the crash. To make sure that the hydraulic fluid was similar to Flight 427’s, they used fluid drained from other 737s. They used a pneumatic cylinder to act like the pilot’s feet, pushing the valve back and forth. The room filled with a steady rhythm of clicks and hisses as the cylinder moved the valve left and right.
Click, hiss, click, hiss. They put the factory PCU through its calisthenics at room temperature, testing it fifty times. It responded normally. They let gaseous nitrogen into the cooler and watched the temperature gauges plummet to minus 30 or 40 degrees, to simulate the cold air at 30,000 feet. Click, hiss, click, hiss. No problems. Finally, they tried two tests to simulate an overheated hydraulic pump, heating the fluid to 170 degrees. Click, hiss, click, hiss. The hot fluid hit the cold valve, but there were no problems. The factory PCU worked great.
They removed it from the Coleman cooler and installed the PCU from Flight 427. Click, hiss, click, hiss. No problems at room temperature. Click, hiss, click, hiss. The frigid unit was blasted with hot fluid, but it still worked fine. It was their last day in Valencia, and the tests were going so smoothly that several people started to pack up and say good-bye. Another theory had been ruled out. It was time to move on.
They had reached the most extreme condition. The PCU was depressurized, frozen with the nitrogen gas, and then injected with piping-hot fluid. They made the test especially severe by performing it with the A and B hydraulic systems separately, so the hot fluid would not be diluted by cooler fluid from the other system.
The hot fluid hit the cold valve. Click, hiss, click, hiss, click, hiss, click, hisssssssssssssssssss.
The hissing changed pitch. The valve had jammed.
“It didn’t come back,” said someone in the room.
“That’s interesting,” said someone else. “Reeeeaaalllll interesting.”
A second later, the arm went back to neutral and began cycling again. Click, hiss, click, hiss.
They stopped the test and talked about what had happened. Did they have a breakthrough? Nobody could be sure. The test conditions were so poorly controlled that any result was questionable. A computer operator who had been collecting test data had mistakenly deleted everything, so they had little evidence of what they had seen. Everyone agreed to try it again.
Click, hiss, click, hisssssssssss. Click, hisssssssssss. The valve was moving slower than it was supposed to. Click, hisssssssssssssssssssssssss. It stuck again.
They agreed that the test should be done again in a more controlled setting. The Boeing team criticized the tests, saying they were too extreme and that the valve could have been damaged. So the next morning, Phillips woke up at 4 A.M. and drove to Parker-Hannifin so they could perform a test to make sure the valve was okay.
The test was crucial. When they had first examined the valve after the crash, they had not found any scratches inside it. If they found scratches now, it would prove that a jam left a scratch, which would indicate there had not been a jam on Flight 427. Also, a scratch would mean that the valve had been altered since the crash, which would rule out any further tests. The whole theory about a valve malfunction would go down the drain.
The Parker technicians took the valve apart, measuring and documenting each piece. They put them under a microscope, examining each surface for scratches or scrapes. They found none and no evidence of a jam. Phillips breathed a sigh of relief.