THE AIR
Air pollution is not the only health hazard in the skies. The nation's overcrowded airways, already clogged by 2,600 commercial and 120,000 private aircraft, pose a more direct threat to life. Last week a single-engine Piper Cherokee, piloted by a plumber on a solo training flight, lopped off the tail section of an Allegheny Airlines DC-9 as the jetliner headed for a landing at Indianapolis' Weir Cook Airport. Eighty-three persons were killed, including the pilot of the private plane. It was the 19th time this year that two planes have collided and the 58th time since the start...