Tuesday, May 05, 2009

Control of Air Traffic

"I fly because it releases my mind from the tyranny of petty things."
-Antoine de Saint-Exupery, pilot and poet

The poet quoted above lived his life entirely in the first half of the last century, when it could be argued that flying was "simpler." If you've been reading this blog for any length of time, you know I post about regulations and procedures quite often, and they are far from simple. My dad once joked to me that being a pilot is a lot like being a lawyer! Early days of aviation were dangerous, of course, and pilots either flew on clear, calm days, or bravely climbed above and descended through the clouds hoping they were closed to their destination, navigating with a compass and making wind corrections, and praying none of those clouds were of the cumulus granite type. [Maybe in a later post I can talk about how brave these early aviation pioneers were, to climb into aircraft hardly more than kites with engines!]

Eventually pilots needed to fly at night, too, to facilitate growing societal needs, prompted by the need for increased airmail service. From the Centennial of Flight website, a short history of the development of more regulated aviation operations:

In the early days of flight, there were no navigation aids to help pilots find their way. Pilots flew by looking out of their cockpit window for visual landmarks or by using automobile road maps. These visual landmarks or maps were fine for daytime, but airmail operated around the clock. In 1919, U.S. Army Air Service Lieutenant Donald L. Bruner began using bonfires and the first artificial beacons to help with night navigation. In February 1921, an airmail pilot named Jack Knight put this to the test with his all-night flight to Chicago from North Platte, Nebraska. Knight found his way across the black prairie with the help of bonfires lit by Post Office staff, farmers, and the public.

Beginning in 1923, the Post Office worked to complete a transcontinental airway of beacons on towers spaced 15 to 25 miles (24 to 40 kilometers) apart, each with enough brightness, or candlepower, to be seen for 40 miles (64 kilometers) in clear weather. On July 1, 1924, postal authorities began regularly scheduled night operations over parts of this route.

Each tower had site numbers painted on it for daytime identification. At night, the beacons flashed in a certain sequence so that pilots could match their location to the printed guide that they carried. Besides the rotating beacon, one fixed tower light pointed to the next field and one to the previous tower, forming an aerial roadway. Official and emergency fields were lit with green lights while dangerous fields were marked with red.

Saint-Exupery became "one of the pioneers of international postal flight, in the days when aircraft had few instruments. Later he complained that those who flew the more advanced aircraft had become more like accountants than pilots."

By the mid-1920s the swashbuckling days of airmail operations had begun to pass. The lone pilot dressed in a leather flight suit who sat in an open cockpit battling the elements to deliver the mail was romantic but inefficient. The Postal Service began to focus on safety and reliability as well as on expanding operations. It established minimum lighting requirements for all airmail stations: a 500-watt revolving searchlight, projecting a beam parallel to the ground to guide pilots; another searchlight projecting into the wind to show the proper approach; and aircraft wingtip flares for forced landings. It also prescribed that all landing fields should be at least 2,000 feet by 1,500 feet (610 meters by 457 meters) to allow plenty of room for landings. As a final safety device, the requirement for a searchlight to be mounted on airmail airplanes was appended to the Post Office's set of requirements.

The use of lighted airways allowed pilots to fly at night, but pilots still needed to maintain visual contact with the ground. A really useful air system demanded two-way voice communication and the ability to find out about changing weather conditions while in flight. But in 1926, pilots could only receive weather information and details about other planes in the air just before takeoff. If conditions changed while flying, the ground had no way to warn them. A pilot, too, had no way of communicating with the ground.

In September 1929, Army Lt. James H. Doolittle became the first pilot to use only aircraft instrument guidance to take off, fly a set course, and land. He used the four-course radio range and radio marker beacons to indicate his distance from the runway. An altimeter displayed his altitude, and a directional gyroscope with artificial horizon helped him control his aircraft's orientation, called attitude, without seeing the ground. These technologies became the basis for many future developments in navigation.

The Centennial of Flight website goes into much more detail about developments in navigation, which you can read more in depth about here. As a sign of the changing times, though, when I do a presentation for kids and I ask them how we can figure out how to get to our destination, more and more are not answering "maps," they're saying, GPS!

Additional navigation technologies are in partial use or development, including the Global Positioning System both to locate and help control aircraft by satellite, the Future Air Navigation System for remote and oceanic flights, and the Communication, Navigation and Surveillance for Air Traffic Management system. These technologies combine the need for point-to-point navigation and for higher quality voice and data communication with the need for air traffic control--the safe separation of aircraft from hazards and other aircraft.

So where I'm trying to go with this preliminary post (more to come) is air traffic control, as I previously posted while referring to an AOPA guide to airspace, which says,

In the early days of aviation, all airspace was uncontrolled, what we today call Class G airspace. Way back when, there were few airplanes, and none had the instruments necessary to fly in clouds. Even at the busiest of airports, traffic density was very low, and the airplanes flew slowly. Although there were no standards for weather conditions that aircraft could fly in, it was generally agreed that if you remained clear of clouds and had at least one-mile visibility, you could see other airplanes and terrain in time to avoid a collision. This was called see and avoid. It formed the basis for VFR flight and remains critical to preventing collisions.
Since we now have the technology to fly in Instrument Meteorological Conditions, or IMC, and there are more airplanes flying to "swap paint" with, the need for Air Traffic Control (an aptly named resource) was developed. Again, from the Centennial of Flight website:

Air traffic control involves monitoring the movements of all aircraft, both in the air and on the ground, in the vicinity of an airport. Its main purpose is to keep aircraft safely separated to prevent accidents. Air traffic control is needed so that the risk of collision becomes extremely low. This can be achieved only by strictly following procedures that are set out and monitored by air traffic controllers, individuals who direct air traffic within assigned airspace and control moving aircraft and service vehicles at airports.

In flight, an aircraft follows en route air traffic control instructions as it flies through successive flight information regions. When it approaches an airport for landing, the aircraft enters the terminal control area where it is monitored by controllers using radar and who constantly tell pilots how to navigate within the area. Controllers also monitor the aircraft all the way to the ground and tell the pilot how to maneuver on the ground to avoid collisions on the ground of the airfield and how to reach its final location where passengers can disembark. Departing aircraft go through a reverse procedure. Overall, the degree of control depends greatly on the weather conditions. In general, the better the weather, then the less the control.

The International Civil Aviation Organization (ICAO), defines the objectives of air traffic control as:

  • Preventing collisions between aircraft in flight
  • Preventing collisions between aircraft on the maneuvering area of an airport and obstructions on that area
  • Expediting and maintaining an orderly flow of air traffic
  • Providing advice and information useful for the safe and efficient conduct of flights
  • Notifying appropriate organizations regarding aircraft in need of search and rescue aid, and assisting such organizations as required
That's enough for today, or else this will turn into a novel. Tomorrow I will talk about pilot and controller communication and more about the use of phraseology contained in the Pilot-Controller glossary and more. Radio communications are invaluable in aviation, but there are many of those "petty things" referred to previously in the quote above, that become HUGE barriers to communication - when they may be needed most. I'll give a few examples.

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