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| Culver Pictures |
| US Army General James H. Doolittle, who completed the first blind flight at Mitchell Field on September 24, 1929. |
He had few options left. The fuel tanks were almost empty, and it was dark. To make matters worse, he was unsure of his location and the fog had completely masked the terrain below, making a safe landing impossible. Soon he would be forced to abandon his O2U-1 airplane and parachute to the ground. Then, unexpectedly, a lighted beacon appeared in an opening in the fog. He seized the opportunity and began the approach to what he hoped would be an emergency landing field. With his landing lights on, he found an opening in the fog and dove beneath it. A tree tore a hole in his wing, and, knowing there wasn't enough fuel to continue, Jimmy Doolittle made the decision to attempt a landing. The left wing contacted a tree during the approach, completely destroying one of two aircrafts operated by the Full Flight Laboratory, based at Mitchell Field, New York. Doolittle walked away unscathed, having learned an important lesson about personal limitations. The flight also confirmed his belief that all-weather flight would never be a reality unless better cockpit instruments and a well-established navigation and communication infrastructure could be developed.
The lighted beacon that guided Doolittle to that field on March 15, 1929, was part of a lighted airway system that had been originally established by the US Post Office to aid pilots flying the mail.
The inception of airmail
The first airmail pilots flew cross-country by following railroad tracks and jotting down notes, describing routes between airfields. In those days, the notes and maps printed for other applications provided the only source of navigation information. This system worked adequately, of course, when the weather was clear and the sun was out. Weather and night flying, however, posed different problems.
night and in conditions of limited visibility severely restricted the utility of the airplane, and it didn't take long for the Post Office to understand that a system had to be developed to allow flight in all types of conditions.
In August 1919, the Post Office approached the National Bureau of Standards for help in solving the problems associated with flight in weather and "fog landing." A number of experiments were carried out, but, under pressure to establish a transcontinental airmail route, the Post Office abandoned further research.
The expense of moving mail by aircraft only during the day and good weather made it impractical. It was imperative that mail be flown not only in the day but at night as well. The success of the airmail system depended on it. The Post Office experimented with a series of lights mounted on towers to guide aviators during the hours of darkness. Lighting the transcontinental route began between Chicago and Cheyenne, and regular night service commenced July 1, 1924.
By 1927, the Post Office, under the Air Commerce Act, transferred 4,121 miles of lighted airways to the Department of Commerce, including 2,041 miles on the transcontinental route. The airways contained 719 airway beacons and 124 intermediate (emergency) fields, each with beacons and airfield lighting. The lighted airways made possible night navigation but were of little help in inclement weather.
If aircrafts were to be dependent on the whims of changing weather patterns while lacking the capability to communicate with each other or those on the ground, commercial aviation would never be able to develop as a viable transportation mode. If air transportation operations were limited to pilotage--navigating when the weather allowed identification of landmarks--or dead reckoning--calculating aircraft position by time in the air and heading--then the precise navigation required to support high-altitude, all-weather flight would be impossible. "That," commented aviation radio expert Henry Roberts, "is why radio navigation is the mainstay of modern air transportation."
The first blind flight
As early as 1920, the impact that electronic navigation and communication would have on aviation was clearly understood. The Manufacturers Aircraft Association, commenting in the Aircraft Year Book in 1921, pointed out that the result of such aids "will be that aircraft will be navigated with a safety and dependability far exceeding that now obtained on steamships." Aviation historian William Leary points out that the utility of the airplane is dependent upon aeronautical telecommunication technologies.
Not only did aviation require navigation technologies to ensure its acceptance as a viable transportation mode; it needed cockpit instrumentation that allowed the pilot to create a "mental model" of the aircraft's attitude, altitude and position during flight in "instrument" conditions. Instrumentation, navigation and communication technologies were the key, and in 1928, Doolittle, working with a grant from the Daniel Guggenheim Fund for the Promotion of Aeronautics, established the Full Flight Laboratory for the purpose of solving problems associated with "fog flying" and "flying blind."
The fund purchased and outfitted two aircraft for instrument flight, the O2U-1 and an NY-2. The NY-2 was chosen for instrument flight experiments. It was fitted with a hood that could completely cover the aft cockpit, simulating instrument flight. Lieutenant Ben Kelsey, who acted as a safety pilot, occupied the front cockpit.
New, more precise instruments had to be developed. The research team, working with the Sperry Gyroscope Company, developed what is now called an "attitude indicator." This instrument provides the pilot with an artificial horizon when the actual horizon cannot be seen. Sperry also designed and built a directional gyroscope that gave more stable heading information, so that pilots could direct their plane on a more precise route.
Early altimeters were not accurate, especially at low altitudes, and could, depending on atmospheric pressure, be off by hundreds of feet. Without accurate altitude information, an instrument-based landing becomes particularly hazardous. Paul Kollsman, a former employee of the Pioneer Instrument Company, solved the altimeter problem. This new altimeter, in combination with the instruments provided by Sperry, gave Doolittle the tools he needed to fly the airplane with no reference to the outside world. But Doolittle still had one other problem to overcome: he had to have a ground-based navigation system in place that could communicate the aircraft's position. This was accomplished by a radio communication receiver--supplied by the Radio Frequency Laboratory and Bell Telephone Laboratory--and cockpit navigation display, built by the National Bureau of Standards (NBS). The navigation signal was broadcast from a radio range designed and constructed by the NBS.
Doolittle continued to experiment and improve cockpit instrumentation. Then, on September 24, 1929--with Mitchell Field engulfed in fog--Doolittle and Kelsey climbed aboard the NY-2. Doolittle put the hood in place while Kelsey lifted his hands for bystanders to see that it was Doolittle at the controls.
The NY-2 began its takeoff roll and soon disappeared into the weather. Doolittle flew away from the field, climbed to 1,000 feet and then turned toward Mitchell Field, navigating on the radio beacon supplied by the National Bureau of Standards. Once he established himself "inbound," he began a gradual descent, landing within a few feet from where he began his historic flight just 15 minutes before.
