The Fate of Yoke Peter

Before a solemn London court of inquiry last week, British science told the world, without excuse or coverup, what happened to Britain's proudest airliners, the ill-starred jet Comets. The inquiry was ordered by Prime Minister Winston Churchill when two Comets exploded over the Mediterranean early this year. Since then, the Royal Aircraft Establishment at Farnborough, headed by Arnold Hall, has been working night and day on a job of detective work that may be the most elaborate in technological history.

Sir Lionel Heald, representing the Crown, opened the proceedings by citing Nevil Shute's novel, No Highway, in which the scientist hero predicts that an airliner will crash because of "metal fatigue."* It was this same metal fatigue, said Sir Lionel, that destroyed the Comets.

Behind Sir Lionel's statement was a fantastic amount of painstaking work. The Comet G-ALYY (Yoke Yoke), that went into the sea near Naples on April 8, left no remains that could be analyzed, but when Comet G-ALYP (Yoke Peter) crashed on Jan. 10 off Elba, its fragments fell into fairly shallow water. Armed with underwater television cameras and special "grab" equipment, a flotilla of British naval salvage vessels and Italian trawlers scoured the bottom, about 500 ft. deep, and fished up the twisted fragments. In all, they got 70% of the structure and 80% of the power plant.

Close to the Tiger. The whole catch was flown to Farnborough. where experts fitted the pieces together on a wooden frame, like a 3-D jigsaw puzzle. Meanwhile, crews of courageous scientists were flying another Comet (Able Victor) on a long series of hair-raising test flights. Careless of their own lives, they tried to duplicate the stresses that had destroyed Yoke Peter. As Sir Lionel described it, "they were going as close to the tiger as possible, hoping it would not get them." Able Victor did not crash; neither did Comet Yoke Sugar, whose fuel tanks were pressure-strained to see if they would explode.

At the same time, a strange structure was rushed to completion at Farnborough. A steel tank (112 ft. long, 60 ft. high, 20 ft. wide) was built around the fuselage of Comet Yoke Uncle. Its wings stuck out at the sides through waterproof rubber packing, and the whole tank, Yoke Uncle and all, was filled with water. Then pumps forced more water into the Comet until the pressure rose to 8 1/4 lbs. per square inch, equaling the air pressure in a Comet's cabin when it is flying at 40,000 ft. While the pressure was rising, powerful jacks moved the wings up and down just as wings are stressed by bumpy air. In this way, all the "fatiguing" effects of a typical three-hour flight could be brought to bear on Yoke Uncle in five minutes.

Patiently, the Farnborough men made "flight" after flight. At last came the event that they had been waiting for. After the equivalent of 9,000 hours of flight, the skin of the cabin near a window yielded to metal fatigue. This gave the essential clue. The scientists found a similar break in the fragments of Yoke Peter near the direction-finder window in the roof. Then they traced, fragment by fragment, what had happened with fearful swiftness to the doomed Comet.

Flaming Spin. The first small crack was enough; air pressure (more than half a ton per square foot) did the rest. The cabin exploded like a bursting balloon; its top flew off; its tail and nose broke away. The wings broke in two, releasing floods of fuel, which ignited. Then the gutted fuselage with its two stub wings dived flaming to the sea in an inverted spin.

To check this theory, Farnborough built 100 small wooden models of the Comet, with parts designed to come apart. They were dropped from balloons or from the top of a hangar. At last one of them broke up in just the way that Yoke Peter did. Its center section spun down to the ground, where its fragments were distributed on the ground in the same pattern that the fragments of Yoke Peter had made on the bottom of the Mediterranean.

Still not satisfied, the Farnborough men constructed a large model of a Comet's cabin in transparent plastic. They filled it with model seats and model passengers. They pumped it full of air at 8 1/4 lbs. Then they deliberately fractured the skin near the direction-finder window and took a motion picture of what happened.

In one-thirtieth of a second three of the forward seats, one of them with a passenger, moved upward toward the break in the roof. The next row of seats followed close behind. As the "suction wave" raced down the cabin, passengers and seats flew out into space. In two seconds, the scientists figured, the cabin of Yoke Peter must have been empty.

This checked gruesomely with the autopsies performed on the bodies recovered from the sea. Most of them had skull fractures and external wounds. "Explosive decompression" (from pressurized to thin air) had burst all their lungs and hearts.

The De Havilland Aircraft Co., builders of the Comets, could not have been happy to hear the results of the inquiry, which placed the blame for the crashes on faulty design and manufacturing methods. But Britain's aircraft industry might well be proud of the inquiry's utter frankness. Its designers are already using the Farnborough testing methods to make sure that such disasters will not happen again.

* Failure of a metal after repeated straining. Small cracks, which sometimes start at tool marks, sharp indentations or other "stress raisers," spread through metal until it breaks. Sufficient strength, correct design and careful fabrication can prevent such failures.

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