Confusion in the Cockpit

For cross-country airplane pilots, an old dream, recently realized, is an electronic navigation system that tells the direction and distance to the airport of destination. The trouble is that it has been realized not in one system but in two. As a result, the flying industry is split wide-open over which system should be adopted.

The Civil Aeronautics Administration, Aircraft Owners and Pilots' Association and National Business Aircraft Association want a very high-frequency system called Omnirange (Omni), which, coupled with Distance Measuring Equipment (DME), does the job handily. OmniDME has already been installed at many airports.

The U.S. Navy, Air Force and Air Transport Association (commercial airlines) want a newer system called Tactical Air Control (Tacan). which was developed by the Navy. As a result of the fight, the airlines have been scared off from spending sizable sums on what might turn out to be the losing system.

Thus, while most commercial pilots rely on Omni for bearing, they find neither DME nor Tacan in their cockpits.

Counting CAA's 231 Omni-DME installations at U.S. airports and beacon stations, and the sets installed by many private aircraft owners, the new systems have cost an estimated $200 million. Last week the House Commerce Committee, after reviewing the controversy and the still-secret development of Tacan, turned up a shocking note: since 1948 the Navy and Air Force have spent $176 million to develop Tacan, but they candidly admit that it is still full of bugs. And Under Secretary of Commerce Louis Rothschild testified that Tacan is three to ten years from being perfected. Said A.O.P.A.'s Max Karant: "The American public has got an accounting coming from the military . . .

Somehow, the public has got to know that they [the military] are destroying Omni-DME and replacing it with a completely unproved new system." Knobs & Dials. The two navigation systems are more notable for their likeness than their difference. Both are rhotheta systems;* both use simple dials on the instrument panel to show direction and distance to destination. Omni-DME is slightly more accurate for distance; Tacan is slightly better on direction. CAA adopted Omni in 1948, and began to install sending stations at airports to replace the radio ranges that told a pilot whether he was to the right or left of his course. Distance Measuring Equipment was added later, along with voice radio (which Tacan still lacks). But the Navy quickly discovered that Omni would not work when the signals came from the rolling, pitching mast of an aircraft carrier, set out to find a system that would.

By 1952 word leaked--out that the Navy-inspired Tacan would make Omni-DME obsolete. Since both systems use the same ultra high-frequency radio band (960-1215), the two are incompatible, just as two broadcasting stations will not work on the same frequency. The Air Force, which found the Navy system less sensitive to rough terrain than Omni-DME, backed Tacan.

International Incident. To settle the controversy the Air Navigation Development Board, a joint civilian-military team, was called in and took Tacan's side. CAA protested, and the State Department pointed out that Canada, England, France, Italy, and other NATO countries had invested in Omni-DME on a U.S. recommendation. Soon ANDE brought out a compromise, i.e., continue Omni (the directional system) until 1965 at least, DME until 1960, while Tacan or some new and better navigation system is phased in. Last week's House Commerce Committee report endorsed the compromise, but suggested that DME be allowed to die after 1958.

* In aircraft engineering jargon, rho is distance, theta is azimuth, i.e., compass bearing to the transmitting station.

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