Jumbo Engine Troubles

While the passenger in a 747 jumbo jet comfortably sips a martini or soaks up the stereo, a rather disconcerting development may be going on inside one of the huge, intricate engines that power the plane. For reasons that still mystify technicians, one or two of the 138 knife-shaped blades in the engine's second-stage turbine may be breaking off in flight and whizzing out the exhaust in showers of tiny metal slivers. The breakoff is so silent that neither passengers nor flight crew notice it, and because it does not lead to fires or loss of power, it usually goes undiscovered until ground technicians check the plane. The engine troubles have caused no dangerous mishaps so far. Indeed, the 747 is history's safest plane, having had no fatal accidents in 391 million miles of flight since the first commercial takeoff in 1970. But the latest difficulties are causing high costs and consternation for airline executives, who are understandably reluctant to trumpet their troubles to the world.

A number of lines, including American, BOAC, TWA, Pan American and Delta, have had to pull engines out of service. Pan Am normally repairs one or two engines a month for second-stage blade malfunctions but so far in July has had to work over twelve engines at New York's Kennedy Airport. Supremely conscientious about safety, Pan Am in some cases has had to transfer passengers to another of its planes or even another airline. Passengers have had to change planes lately in Teheran, Lisbon and Frankfurt.

The difficulty centers on the fan blades in the Pratt & Whitney JT9D-3A engines, which were put on early models of the 747. What is eerie about the problem is that it continues to occur even though Pratt & Whitney has supplied the airlines with new blades made of higher heat-resistant alloys. Pratt & Whitney is now sending to the lines a comprehensive "modification kit" that changes parts of the engine and converts it to the equivalent of the power plant used in the new 747s. These later-model planes have not had an abnormally high rate of blade failure. Trouble is, the company is not turning out the kits as fast as the lines require, and the modification program will not be completed until 1974.

Travail. Meanwhile, the repair bill is climbing; it averages $100,000 per engine. Fan-related repair costs this month have cost Pan Am alone some $1,200,000. Pratt & Whitney's engines are covered by such a complicated warranty that lawyers may become rich arguing over how much of the repair will have to be paid for by the manufacturer and how much by the airlines.

The huge, advanced jet engines have long caused concern among airmen. The new generation of power plants has required advances in high-temperature metallurgy that strain the boundaries of technology--and sometimes shatter bankrolls. Rolls-Royce went broke last year because costs for a daring new engine being built for Lockheed proved far greater than expected. Pratt & Whitney suffered much travail with its earliest models of the 747 engines. In years past, airlines did not have to weather such severe problems, in part because new engine versions were first tried out and perfected on military planes. But there were no such military tests for the 747's engines. For the airlines, which have just lately pulled out of a long financial tail spin, the turbulence of advanced engine technology could be most expensive.

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