This is the third in a series of articles looking at the impact of NextGen on GA pilots.
As we race through each generation of the National Airspace System (NAS), technology clearly is the biggest driver contributing to its evolution.
Last month we discovered that the expansion of the NAS was started by the U.S. Postal Service. Because of the inability to fly at night, navigational beacons were first introduced by using bonfires spaced a few miles apart. This gave pilots beacons of light to fly by during night operations, improving safety and increasing the amount of mail delivered throughout the U.S.
This month the power of electricity comes into the picture, beginning a series of advancements in the NAS that will eventually become our new Next Generation Air Traffic Control System (NextGen).
Bonfires gave way to the electric light bulb, which allowed navigational beacons to be operated from remote locations, as well as affixed to towers for even better visibility. It was these 51-foot towers spread throughout the country that really started driving the air routing system.
By 1923 the Post Office started building a network of transcontinental lighted airways incorporating these 51-foot lighted towers. Each tower was numbered and that number was posted on each tower for day-time flight. With 500 watt bulbs, these towers would flash a definable sequence during the night, giving pilots the ability to identify each tower, providing a precise location of where they were.
To improve the efficiency of the system that much more, each beacon was built with narrow light dispersion characteristics bringing forth a highly directional beacon spaced as much as 25 miles apart. Each beacon would point to the next, allowing pilots the luxury to fly from one airport to another strictly by using lighted beacons.
In 1926 the Commerce Department took over the responsibility for the building and maintenance of these new lighted airways. By 1933 there were 1,500 lighted towers covering more than 18,000 miles of airways. During this expansion, more safety features were introduced, with identifying colors depicting emergency airfields in green and dangerous airfields in red.
The next important hurdle was to provide pilots with enough informational data during pre-flight so they would have a relatively good idea what to look out for during each trip. This was a good effort, however conditions could change rapidly, causing flights to be diverted, which impacted safety while at the same time delaying the mail service.
Pilots needed a way to communicate with the ground for current conditions. Technology brought to aviation a communication system using radio telegraph and typewriters transmitting current conditions to each pilot with a transmission range of as much as 50 miles. In 1927 a radio communication was successfully demonstrated between an airmail plane flying on a transcontinental airway and Bellefonte, Pa. This brought on a new recorded communication distance of 150 miles.
During this same time period the expansion of radio technology designed for voice and navigation systems began to come into the forefront of aviation. In 1928 the technology of radio navigation took center stage. It was called the Four Course Radio Range or, as many named it, LFR (Low Frequency Radio Range). Brought to fruition in late 1926 by the Ford Motor Co., LFR was, in fact, the beginning of instrument flight, allowing airplanes to be flown in just about any kind of weather, both for day and night flying.
The Bureau of Standards installed as many as seven communication stations by October 1928. By the summer of 1933, there were 68 stations placed strategically 200 miles apart. By the beginning of 1940 there were as many as 165 stations slated for construction.
The LFR system consisted of four antennas strategically placed in a square (Figure 1), transmitting a 1000 Hz tone. Two antennas transmitted two Omni Directional patterns with the Morse Code sound for the letter A (Dot Dash Dot Dash), while the other two antennas perpendicular to the first transmitted two Omni Direction patterns of the Morse Code sound for the letter N (Dash Dot Dash Dot) (Figure 2).
If an airplane flew within the intersection of an A Circle and an N Circle, the dashes and dots joined together, creating a solid 1000 Hz tone. This was an extremely reliable system not only for direction from one point to another, but also for supplying pilots with enough information to tell where they were in relationship with each station. For instance, if an aircraft was within the A transmission circle only, the pilot would know that he was either west or east of the station. If positioned from the opposite direction within the N transmission circle, his aircraft was either north or south of the station. Since these transmissions were Amplitude Modulated (AM), the further away the aircraft was, the lower the sound level. The closer the aircraft was to the station, the louder the sound. Just listening to these stations and having charts on board, a pilot could locate exactly where his aircraft was positioned.
It becomes quite obvious the direction electronics is taking us. Of course, the NextGen system incorporates a much higher level of electronics and technologies for it to operate with the accuracy necessary for today’s — and tomorrow’s — National Airspace System.
Next month: We will move into NDBs (Non-Directional Radio Beacon) and VORs (Very High Frequency Omni-Directional Range), followed by GPS. You get through all this and NextGen will be a cake walk!