Keeping Planes in the

Commercial aviation expanded at a much faster rate than national weather services were equipped to support it during the 1920s. The rapid acceptance of air mass and frontal analysis throughout Europe attests to the desire to provide better flight forecasts for passenger and airmail flights. Upper-air data collection by means of pilot balloons, balloon-sondes, and aircraft assisted in this effort.

Weather services in the United States remained at a disadvantage compared to those in European nations. With a limited budget and a lot of territory, aviation forecasts were completely inadequate before 1926. The Weather Bureau could not afford to increase the number of daily observations or the number of surface and upper-air observation stations. To keep track of critical flight weather conditions, the bureau estimated that it needed one station every 250 miles (402 km) along air routes, known as airways. These special weather offices, called airways stations, needed to be connected by telephone so that information could be called ahead to the next station if conditions were deteriorating when a pilot was in the air. Existing telegraph circuits, operated by Western Union, needed to be adjusted to carry the weather observations at 6 a.m. instead of during the 90-minute time block reserved for weather reports after 8 a.m.

As all of these technical and financial problems stacked up, the Weather Bureau drew withering criticism for contributing to a number of high-profile aviation accidents because pilots had not received adequate warning of adverse flying conditions. On May 20, 1926, Congress passed the Air Commerce Act, requiring the Weather Bureau to provide aviation forecasts necessary for flight safety. A

An airmail pilot prepares to take off. (NOAA)

funding bill passed in July provided the bureau with the financial resources necessary to assign experienced meteorologists to all major landing fields and establish 22 pilot balloon stations on the New York-San Francisco flight route. Additional funding in 1928 added 18 more meteorologists to extend the airways system for another 6,000 miles (9,656 km).

By 1928, airways stations were relocated from city offices to major airports. They also operated 24 hours a day instead of between 8 a.m. and 11 p.m.—a huge advantage for pilots who wanted to get an early start in the morning. With the financial backing of the Guggenheim Fund for Meteorology, the bureau added a new Pacific airway extending from San Diego, California, to Seattle, Washington. The fund also enabled the Weather Bureau to send one of its meteorologists to Bergen to study the effects of fog, haze, and thunderstorms on flight safety.

Aviation forecasting got a significant boost when teletype replaced telegraph in 1928. By 1930, the Weather Bureau had extended teletype

Criticism of aviation forecasts made by the world-famous pilot Charles Lindbergh helped lead to the passage of the Air Commerce Act of 1926.

(Library of Congress)

over 8,000 miles (12,875 km) of airways, connecting all airways stations with the Washington, D.C., headquarters and allowing for complete data exchange. Equipment breakdowns were common in the early years of the program and meteorologists relied on telephone and telegraph in emergencies. Major airport control towers used radio to communicate weather information to pilots while they were still airborne, transmitting updated weather observations every 30 minutes.

As meteorologists and pilots gained more experience with weather conditions that could adversely affect flight safety, additional data and rules were introduced. In 1929, the Weather Bureau added ceiling and visibility information to observations. Beginning in 1930, the Department of Commerce restricted pilots from taking off when the ceiling was lower than 500 feet (152 m). Weather observers were then under pressure to determine the exact ceiling, particularly when the ceiling was close to the limit. Sometimes pilots would fly anyway and sometimes they would be upset because they could not fly. The Weather Bureau always made the point that they just made the observations; they did not tell pilots whether to fly or not—a situation that prevails to this day.

As the decade closed, meteorologists were providing considerably more information via teletype. In addition to normal temperature, pressure, and wind measurements, hourly teletype reports, dubbed aviation hourlies, provided information on how snow, rain, thunderstorms, or gusty squalls were affecting landing field conditions. Aviation forecasting showed tremendous improvement throughout the 1920s, only to be curtailed by fiscal problems caused by the Great Depression of the early 1930s.

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