Our cover of Oct. 7, 1957, showed the first Lockheed L-188 Electra mid-range transport after completion of structural assembly at the company's plant in Burbank, California. 

Lockheed had already taken orders of 141 of the aircraft, which was designed to carry up to 100 passengers and offer superb operating economics. 

The first prototype flew on Dec. 6, seven weeks ahead of schedule, and the four-engine turboprop entered service with Eastern Airlines in early 1959. But a series of crashes in 1959 and 1960, including two where the aircraft disintegrated in mid-air, led to order cancellations. 

Wind tunnel tests at NASA's Langley Research Center indicated that a stiffness in the Electra's engine had triggered an interaction known as whirl mode, which resulted in a catastrophic flutter of the wing. 

Lockheed solved the problem by redesigning the engine mounts, nacelles and cowlings and strengthening the wings, but the damage to the Electra's reputation was lasting. Just 170 were ultimately built. 

However, from the Lockheed Electra, went on to develop the P-3 Orion. More than 730 were built and remain in worldwide service today. 

The P-3 is one of only a handful of military aircraft to have seen more than 50 years of continuous service with the U.S. armed forces. 

See the images in the feature on page 65 of the Oct, 7, 1957 issue. 

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