The Helpful Wind

If Columbus had sailed due west, the "prevailing westerlies" of the North Atlantic might have battered his caravels back to Europe. But by luck, sailor's hunch, or a simple desire to sail in warm weather, he detoured south to the Canary Islands, picked up favorable winds. Since then, transatlantic sailing ships have used the Columbus system, often sweeping miles out of their straight-line courses to take advantage of friendly winds.

To steamships, the winds are nothing but a nuisance. Steamers go out of their way to dodge a hurricane, but in normal weather they stick to a "great-circle course"--the shortest path between two points on the earth's curving surface. But ocean-flying airplanes made the winds important again. Last week the PICAO (Provisional International Civil Aviation Organization), which provides planes with valuable weather information, was planning ways to standardize its service internationally. The idea is to help pilots of all countries and languages make the winds work in their favor.

When airplanes follow a great-circle course, they often buck head winds all the way. A longer course to the left or right may give them helpful tail winds. How to find such winds has been the problem. The pilot cannot depend, like a sailing-ship captain, on the average wind directions over long periods of time. He crosses too quickly for that. A strong head wind lasting only a few hours may upset his schedule as much as if it kept blowing for weeks.

A Look Ahead. The answer is "pressure pattern flying." Certain winds are pretty likely to be associated with certain weather conditions. An area of low pressure in the northern hemisphere, for instance, is surrounded by winds blowing counterclockwise (see map). Around high-pressure areas, the wind blows clockwise. If the pilot knows which he is approaching, a low-pressure or high-pressure area, he can set his course to take advantage of the most favorable winds.

He needs to know the barometric pressure throughout the flight. His ordinary altimeter (essentially an aneroid barometer) is not enough, for its readings vary with pressure changes due to either altitude or weather. The problem is solved by the radio altimeter, which measures the plane's altitude electronically. Its readings, combined with barometric altimeter readings, give the actual pressure of the air through which the plane is flying.

A Push from Behind. If the pressure keeps falling, the pilot can tell that he is approaching a low-pressure area. Heading towards Europe, he would veer south (as on the map) to pick up a tail wind. Flying west, he would veer north, and get a similar boost. Radioed reports from ships, from shore or from other planes help him figure out the situation. Frequently a properly plotted pressure course, though covering a longer sea distance, saves more, than an hour on a transatlantic flight. It also saves fuel and money--a modern, four-engined airplane costs $1,000 an hour to operate.

Pressure flying continues to grow more & more exact. Nowadays, airplanes in flight send hourly weather reports to the CAA's station WSY in New York. WSY edits the information and broadcasts its essentials at 25-minute intervals to other planes. By merely listening and figuring, a pilot can tell where to find the friendliest tail winds.

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