The Fatal Flaw

In the Burbank, Calif, headquarters of Lockheed Aircraft Corp. last week, 50 commercial aviation leaders gathered to hear the answer to one of U.S. aviation's most fascinating and terrible riddles: What caused two Lockheed Electras to come apart in the sky over Texas and Indiana, killing 97 persons? To representatives of the Air Line Pilots Association and of 13 airlines (six of them foreign) now flying 136 Electras, Lockheed gave the answer: the doomed Electras' wings were torn off by a violent wing fluttering caused by a weakness in their engine nacelles.

Enormous Forces. The Electra's troubles, said J. F. McBrearty, who directed a $2,500,000 Lockheed inquiry that kept 250 engineers and technicians busy for two months, "have been one of the most profound engineering problems that have confronted our company in three decades of airplane building." As McBrearty ex plained it, the two Electras were brought down by a combination of factors, none of which would have been enough to wreck the planes by itself. The basic flaw was that the support structure of the wing nacelles, holding the plane's turbo prop engines, was not built sturdily enough. When damaged or weakened by such a common occurrence as a rough landing, the struts beneath the four engines no longer held the engine nacelle tightly enough in place. Said McBrearty: "All of our tests and calculations substantiate the conviction that some element of damage existed in the power-package-nacelle area of both Electras prior to their accidents." Even then, the Electras might have flown in relative safety except for violent air turbulence encountered at the Electra's speed (more than 400 m.p.h.). When the planes hit rough air, the impact apparently set their weakened nacelles to shimmying, and the engines swayed so that the propellers no longer revolved at right angles to the wings. As the propellers wobbled, they set in motion a gyroscopic twisting force that wrenched off a wing, probably at a spot close to the fuselage. All of this could take place in but 30 to 40 seconds.

Over the California mountains, Lock heed test pilots had purposely flown test Electras into turbulent air at high speeds. Apparently because the planes' struts had not been weakened, nothing happened. But when company engineers, in wind-tunnel tests, purposely weakened nacelle struts to about the same condition as those on the crashed Electras, the fatal chain reaction began. The company had its answer. During all of this testing time, the Federal Aviation Agency had allowed airlines to fly Electras so long as their speed was held to a conservative 329 m.p.h. at 15,000 feet, thus removing one of the known factors in the trouble. Lockheed now feels sure that it can remove the other by strengthening both the nacelles and wings to "preclude the possibility of such a coupling of forces."

Heavy Blow. As soon as the FAA confirms its findings, the company will begin modifications of the Electra (including 34 awaiting delivery). It hopes to finish by year's end. Lockheed Chairman Robert Gross predicted that the modifications will cost about $25 million. There was a chance that the airlines would assume part of the cost, rather than engage in a court battle with Lockheed to determine responsibility.

Electra's troubles have already been a heavy blow to Lockheed. When the planes were first delivered, airlines complained about vibration, and Lockheed spent some $7,000,000 changing the slant of the planes' engines to correct it. Since the new troubles, Lockheed's stock has been sliding steadily, last week closed at 20 1/2 v. its 1960 high of 32 7/8. Worry among stockholders has grown so great that last month Bob Gross took pains to point out that Electra sales in 1960 will account for only about 15% of total sales of more than $1 billion. To make up the Electra losses, he is counting on the steady growth of the company's electronics organization, as well as on such standbys as the Agena satellite and Polaris missile, which account for close to half the company's dollar volume.

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