Milestones Old Faithful

Air and Space Magazine ^ | 05/01/2010 | George C. Larson,

[ErnstStavroBlofeld]

In May 1985, a Boeing 767 operated by Trans World Airlines became the first twin-engine airliner allowed to fly directly from St. Louis, Missouri, TWA’s hub, to Frankfurt, Germany, without altering its course to comply with an international requirement that it never be more than an hour’s flying time from an airport where it could land. The rule harkens back to the days of piston engines, which were so unreliable that at least four were considered necessary for a long flight over the ocean or hostile terrain. Even with four engines, airliners sometimes had to ditch—most notably the Boeing 377 Stratocruiser, three of which had engine and propeller problems that forced them to land in the water.

With the arrival of turbojet propulsion on the de Havilland Comet and Boeing 707, both of which had four engines, the airlines began to build a record of engine reliability that is now nearly perfect. Engineers could calculate the odds that more than one engine might have to be shut down in flight, and determined that with three engines, that possibility was so remote as to be virtually nonexistent. In 1964, all three-engine jets were exempted from any sort of time rule, and the International Civil Aviation Organization expanded the rule for twin-engine jets from 60 minutes to 90. Engines are rated by dispatch reliability—a measurement of how many flights are delayed or cancelled because of engine problems—and today, it is not unusual for an engine to have a rating in excess of 99.9 percent

[montanajoe]

I guess the Iowa crash of the United DC-10 back in the summer of 1989 was nonresistant...