Common Complexity

Electronics offers a bewilderingly rich array of gadgets to guide aircraft. Some have serious faults; some are underdeveloped, too expensive or too heavy; some do not suit all types of aircraft or all types of pilots. The problem for Government committees, cooperating with civil and military airmen, is to select from this plethora a common system that will enable instrument-flying pilots to find any airport, avoid all obstacles and land safely on an invisible runway.

In July of 1947, Special Committee 31 of the President's Radio Technical Commission for Aeronautics undertook the selection job. The Transition Phase built around electronic equipment that had already been designed, was to be finished by 1953. This month, halfway through the target year, the Transition Phase is far from over. But pilots have more guides than ever before to get across country and into airports.

Distance & Direction. In addition to the old four-beam, low-frequency (200-400 kc.) radio ranges, the airways are now dotted with very-high-frequency (108-118 mc.). Omniranges (TIME, Dec. 20 1948). They cover limited distances (200 miles at 20,000 ft.), but are far more versatile than the old-style ranges. Almost unhampered by static, they give the approaching plane a straight-in heading from any direction. Rather than flying on a narrow, crowded beam, a pilot can tune his Omnirange receiver to the desired station, then read his course on a dial.

On some air lanes, distance-measuring equipment (DME) is being installed along with the Omniranges. A small transmitter in the approaching plane sends out brief pulses of radio energy. At the Omnirange station, another transmitter answers with a similar signal. Aloft, complicated circuits translate the time between pulse and answer into the plane's distance from the Omnirange, shown on a handy dial.

DME is not yet perfected, but its dials should soon be as reliable as a well-checked speedometer. Meanwhile, technicians have worked out another trick for Omnirange-DME. By adding a small electronic brain which automatically solves the problem in angulation, it enables a pilot with DME equipment to set an accurate course to an airport miles away from the nearest Omnirange.

Traffic & Landing. For foul-weather landings, the common system includes both radar-directed, ground-controlled approach (GCA) so popular with the military, and the instrument-landing system (ILS) that is preferred by airline pilots. At airports equipped with both systems, planes can make their final approach down the ILS radio beam, while alert ground crews give extra guidance through GCA.

With all their electronic cunning, scientists are steadily weeding out possibilities for human error. In the process, they have packed the airplane with a hefty load of gear. Well-equipped modern airliners are likely to carry both low-and very-high-frequency communication sets, a couple of low-frequency radio compasses, a radio altimeter, perhaps even an airborne radar.

So great is the supply of gadgets that every development brings up new questions. Should all airways be handed over to the military radar network that guards them already? Should all planes be forced to carry Omnirange and DME equipment? Such questions must be answered before a final policy for air-traffic control can be laid down. Before that happens, planes may be so crammed with instruments that their passengers will have to stay at home.

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