Comforting Tracks

The air lanes now have a new and friendlier look to airplane pilots. Dotted along the air lanes at 100-mile intervals (or less) are squat steel towers topped with curious structures like horizontal wheels. These are "omniranges," which tell a wandering airplane pilot where he is, where he is heading, and how he can get elsewhere quickly if he needs to. Last week the Civil Aeronautics Administration announced that 300 of its projected 409 omniranges were in operation.

Principal air navigation aids in the days before "omnis" were radio ranges. They were better than nothing, but they did not tell the pilot enough. What they did was provide four "beams," which he could follow from range to range or to a field. But the beams were far apart, and finding them was a hard and time-consuming job. Furthermore, the ranges used low-frequency radio, and in stormy weather static made a hash of their signals, just when they were needed most.

Two Needles. Omnirange uses "very high frequency," is static-free. It is complicated electronically, but it makes things simple for the pilot. Each omni sends out a radio signal that is different for each direction from the station. Receiving apparatus on the airplane detects the variation in the signal, and so tells the pilot where he is in relation to the station.

There are several receiving sets on the market. A typical one has two needles for the pilot to watch: a "to-or-from" needle and a "left-or-right" needle. The pilot's first step in "omnigation" is to tune his set to the nearest omni's frequency and wait for it to identify itself by voice or code. Then he looks at his to-or-from needle, which tells him at once whether he is heading toward or away from the omni.

Next step is to turn a dial slowly until the left-or-right needle comes to rest in the center of its scale. Then the pilot looks at the dial and reads off his directions from it. By keeping the needle centered, he can follow the "track," as pilots call it, directly to the omni station. Or he can tune in another omni and find his direction from it too. The two tracks, drawn on a map, give at their crossing the position of the airplane.

Omni to Omni. When a pilot wants to fly cross-country, he can hop from omni to omni, flying out along a track from one and in along a track to the next. If he does not want to pass near any omnirange, the procedure is slightly more complicated, but the pilot never need feel lost; the friendly tracks fill the air with comforting advice.

Omnirange has one disadvantage. Its VHF waves (112 to 118 megacycles) go out straight from the station; like television waves, they do not follow the curvature of the earth as the low-frequency-range signals did. Thus, omnirange signals cannot be picked up dependably beyond the "line of sight." The fault is not serious: when an airplane is flying at 5,000 ft., the line of sight is an ample 100 miles. Counting military installations, there are now about 360 omnis in the U.S. Soon there will be 100 more, and the system is scheduled to spread to foreign countries. Some airlines (e.g., American) are already fully equipped to use omni; others are converting to it rapidly. Its safety and security appeal to all pilots. Says American's chief engineer, "Dan" Beard: "Imagine you had the windows of your car whitewashed. Then you cut a hole in the floor and could follow a white line on the road. That would be track--and track is what omnirange gives you."

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