Phillips’s approach on the hill followed the classic NTSB method. He had his team examine each component from the flight control system, even if the component was unrelated to the rudder. It was far too early to jump to conclusions. They did not want to zero in on one theory too fast, the way the investigators of the Knute Rockne crash did, only to find later that they had neglected something important.
His team found the other mangled flight controls—the ailerons (the wing panels used for banking and turning), and the flaps and slats (the devices on the front and rear of the wings that provided extra lift during takeoffs and landings). For each one, they also found the actuators—the hydraulic or mechanical devices that moved the panels. Phillips’s team carefully measured and photographed everything, to record whether the panels were up or down, right or left at impact. By measuring where things broke or where they bent, they were able to put together a snapshot of what the plane was doing when it struck the road.
The group spent a lot of time examining the device that moved the rudder, which was called the power control unit. Amazingly, it had survived the crash with virtually no damage.
“This thing is in pretty good shape,” Cox said when he saw it.
Phillips was relieved. He knew that the rudder unit would be the subject of many tests. One of his biggest regrets from the Colorado Springs crash was that the rudder system had been badly damaged, making it difficult to test some of the theories. Phillips’s first goal with the USAir wreckage was preservation. He needed to make sure the evidence wasn’t altered when his team moved it from the hill to the hangar and then shipped it to a lab for a detailed inspection.
A yellow construction crane was brought in to lift the big tail section onto a flatbed truck. Workers tied nylon straps around it and stood back as the diesel engine strained to pick it up. When Cox heard the engine groaning, he worried for a moment that the crane might drop the huge piece. But the tail lifted slowly into the air, and the workers used ropes to direct it onto the truck. Once it was secured, the truck drove to the decontamination station so it could be sprayed with the Clorox solution. The process reminded Cox of his planes’ being de-iced. The wreckage was covered with a tarp to hide it from the snooping eyes of the media, and then it was driven to the hangar.
Phillips and his group decided to send the key pieces to two labs on the West Coast. Most devices from the rudder and aileron systems would go to the Boeing Equipment Quality Analysis lab outside Seattle, which was regarded as one of the best places in the world for forensic analysis of a plane crash. The rudder power unit would go to a Parker Hannifin plant in Irvine, California, where the units were manufactured.
The rudder unit had been carefully cut from the tail of Ship 513. Its hydraulic lines were capped to keep the fluid inside. It was packed in a padded trunk and sealed with several layers of shipping tape. Phillips and other members of the group signed their names on the tape so it would act like police evidence tape. When Phillips got the box on the West Coast, he could check the tape to be sure that no one had opened the trunk and tampered with the evidence.
9. PIPSQUEAK
Hidden in the tail of every 737 was a hydraulic device that acted as the muscle to move the plane’s big rudder. It was about the size and shape of an upright vacuum cleaner and was known as the power control unit, or PCU.
Inside the PCU was an ingenious valve. It was shaped like a soda can and was strong enough to move the rudder when the plane was going 500 miles per hour. The gadget had an impossibly dull name—the dual concentric servo valve—but engineers used an amusing hand gesture to show how it worked. They curled the fingers of one hand to create a hole and then stuck their index finger in and out, as if they were demonstrating sex.
That was how it worked. When a pilot pushed on a rudder pedal, he moved a tube the size of a pencil in and out of the soda can. Holes in the tube allowed hydraulic fluid to squirt against a piston, which pushed the rudder to the right or left.
The 737 rudder valve was unique because it had two tubes, one inside the other. Both moved back and forth. That design was revolutionary in the arcane world of hydraulics. It allowed Boeing to use one power control unit instead of two, which helped it fit in the tight confines of the tail and trimmed at least fifty pounds off the final weight, saving airlines thousands of dollars in fuel over the life of a plane.
The valve-within-a-valve also had an important safety feature. If one tube jammed, the other one could still move and neutralize the rudder.
At least, that was how it was supposed to work.
Investigators had suspected a problem with the rudder valve in the Colorado Springs crash, but the evidence had been too sketchy. The valve was damaged and difficult to test. This one, however, was in perfect condition. So Phillips’s trip to the West Coast had the potential to wrap up the investigation quickly and neatly. All he needed was to find a tiny flaw, and the mystery would be solved.
But as he flew to Seattle, he wasn’t fantasizing about solving the case. He was being his usual cautious self, fretting about the test plan for all of the flight controls—not just the rudder—to make sure he didn’t forget anything.
“We can’t just stay focused on the rudder,” he told his group when they gathered in a lab at Boeing’s big plant in Renton, Washington. There was mounting evidence pointing to the rudder, but Phillips did not want to exclude other possibilities and then discover he had missed something crucial. He said he would be open to any idea, any test. “No question is too trivial.”
The lab, in a giant gray building beside Interstate 405, about ten miles southeast of Seattle, resembled a high school science classroom, with drab yellow walls and lots of counter space for tests. The technicians who worked there were the unsung heroes at Boeing. They were a notch lower on the food chain than the engineers who got most of the glory, but they were just as important. They tested hundreds of airplane parts every year to make sure they were safe and durable. They could figure out why a window cracked, why an actuator leaked, how to improve a toilet seat.
They had lots of gadgets to help them examine broken parts—microscopes that let them see tiny imperfections in plastic and borescopes that could peek inside a device. The technicians were like a band of renegade nerds. For kicks, they once used the borescope to check out a guy’s ingrown nose hair.
Phillips’s group planned to test anything that could have played a role in the crash—the main rudder power unit and its backup, the standby PCU; the rudder trim actuator, which adjusted the rudder constantly to keep the plane flying straight; and the hydraulic devices that moved the ailerons. The wreckage arrived in big wooden crates, all sealed with tape, just as the rudder crate had been, to make sure no one tampered with the evidence. Everything reeked of Clorox.
Phillips, Cox, and the other team members met in a conference room to decide how each piece would be tested. Phillips insisted on a consensus for every step. They would not proceed until all team members—from the NTSB, the FAA, Boeing, ALPA, and the machinists union—agreed.