Aviation: Middle-Age Spread

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Examining the wreckage of the BOAC airliner that crashed near Mount Fuji in March, U.S. and Japanese experts detected hairline cracks in the Boeing 707's shorn-off tail assembly. By last week the examination had spread to scores of Boeing jets around the world.

Though the cause of the Tokyo crash remains unknown, the Federal Aviation Agency as a result ordered foreign and domestic airlines to inspect and, if necessary, repair tail assemblies of 190 older Boeing 707s and 720s. So far, they have found 61 planes with tiny fissures around the bolt holes where the tail is fastened to the fuselage. In most cases, the affected aircraft have been airborne again within two days.

The FAA directive reflects more than anything else the fact that the pioneering jetliners have reached middle age. The first 707s went into service back in 1958, and some of the earliest have since logged more than 250,000 flight hours. The hairline cracks are caused by metal fatigue that commonly develops in high-time aircraft at points where flex and strain occur; even in the DC-6, one of the sturdiest planes ever built, fissures were discovered in a number of wing spars in 1960. To date, said the FAA, no aviation accident of any kind has been attributed to such defects.