Progress in Air Traffic Control

For many Americans, air travel is a common place experience today. Near many of our major cities, municipal airports have evolved into international terminals from which we fly with safety across the country and around the world. More and more Americans fly every day on business and on pleasure trips, to meet a schedule or to make the most of time available. Fast, efficient, comfortable, and safe, air travel is relatively inexpensive now. It will cost even less in the next few years. Airlines envision coast-to-coast fares at bus ride rates. As the cost of air travel goes down, more and more people will want to fly. More and more planes will therefore take off to fill the already crowded sky. Private aircraft, military planes, and commercial airliners fill major airways even now, and hold over terminals near the major cities of America. The growing numbers of these planes, the constantly increasing speeds and altitudes at which they fly, all these factors complicate the problem of air traffic control. How are collisions prevented in this growing traffic in the air? How can the safe passage of air traffic continue as the number of planes in the already crowded sky continues to increase? These airline passengers are actually safer here today than they might be riding in private automobiles on the ground below. Modern air traffic control measures make this so. But what is air traffic control? What does it involve? How has the control of traffic in the air improved since the good old days when a handful of leather hats, early military pilots, had the whole of the blue sky all to themselves? At first, it was just a question of seeing and being seen. All air traffic was controlled by visual flight rules, VFR. You could see another plane approaching yours, and you had time to get out of each other's way. But military aircraft, and later commercial planes, were developed to fly at faster speeds and higher altitudes, depending increasingly on instrumentation and on control from the ground to get them safely through the air. For instance, two jets, each of them cruising at 600 mph, will close at speeds up to 1,200 mph. They move so fast, they may be committed to a collision when the pilots first sight each other. Before either pilot or plane can react, the moment of impact might be reached. if it were not for control from the ground with radar, radio, and other safety measures. Instrument flight rule IFR conditions now control their flight. Radar was born as a World War II military device, one application being the detection of enemy raiders. Radar transmits a signal which is reflected by most objects the signal meets. This reflected signal is echoed back to the radar antenna. It then appears on a scope as a visual display or blip. A single blip indicates two things: azimuth, the direction of the object from the radar antenna, and range, the distance between the object and this antenna. Successive blips indicate the direction in which the object is moving. Radar came at a fortunate time, just as speed was bringing an end to the old days when VFR was the only method of flight control. As work progressed in this new field, it became apparent that many objects reflected weak signals back to the radar antenna that were indistinguishable on the scope. Engineers decided to install a special radio called a transponder into the aircraft to strengthen this return signal. Later, it was determined that the signals transmitted by the transponder could consist of several information pulses responding on separate frequencies. This set the stage for using various modes and codes. A mode is a method of electronic interrogation determined by the pulse spacings. Each mode has a different spacing. The reply made by the transponder is a code represented by a series of information pulses occurring within the bracket space for the particular mode in use. Thus, the transponder replies to a mode of interrogation with a particular code, depending on the predetermined mode setting made to the transponder. The present system uses three modes with related codes, modes 1, 2, and 3A, each having a different pulse pattern. Modes 1 and 2 are used exclusively by the military. 3A is the common mode for air traffic control used by both civil and military aircraft and air traffic control facilities. The limited number of codes, 64, presently available in mode 3A, has enabled civil and military air traffic control facilities to make limited selective identification of those aircraft equipped with transponders. Different coded replies appear as different blips on the controller's scope. This aids the controller in identifying and vectoring individual planes through what may be a maze of traffic in the air. But because the number of these codes is limited to 64, it is still necessary to establish voice contact with the pilot to identify him and steer him through. It is always necessary to verify by voice contact the pilot's altitude, which is not indicated by the blip. To aid him in remembering the information received by voice, the busy controller uses plastic shrimp boats to keep track of his targets. Thus, the controller has to maintain voice communication with the pilot. The pilot has to answer him. The busy pilot therefore remains a link in the communication system, connecting him to an equally busy controller on the ground. The Federal Aviation Agency, FAA, has primary responsibility for the safe and efficient passage of aircraft through the nation's airspace. Since both civil and military aircraft use the same airspace, FAA and and military have always worked closely with one another. FAA air route traffic control centers like this one have grown out of this cooperative effort and common experience. Also, military traffic control facilities have profited from the fact that for years the FAA and the military have made joint use of radar to affect better air traffic control over and approaching the United States. From the beginning, FAA benefited from the development of early military equipment and techniques. The state of the art advanced in response to the exacting all-weather, around-the-clock demands of military flight and its urgent need for the positive identification of unknown objects in the air. The control of military aircraft involves the most sophisticated radar and communications equipment available. Using this precision equipment, the controller gives specific instructions to the pilot. Air Force 971 approaching glide path. Begin descent. Begin descent. 1 1/2 mi from touchdown, 360 is your heading. 4 mi from touchdown. Turn right heading 003. 003 is your new heading. On glide path. Gear should be down and locked. Show landing light. 003 is your heading. On course, on glide path. 003 is your heading. 2 and 1/2 mi from touchdown. You are clear to land. Now going 10 ft above glide path, adjust your rate of descent. 5 ft above glide path, on glide path, on course. 2 mi from touchdown. Dropping 10 ft below glide path, adjust your rate of descent. On glide path, on course. 003 is your heading. 1 mile from touchdown. On glide path, on course. 003 is your heading. On glide path, on course. Over approach lights. On glide path, on course. Over end of runway. Take over visually, complete landing. Contact ground control 275.8 as soon as practical. Because of the anticipated increase in air traffic, the FAA air traffic control facilities will require even more support in the future. In the airspace over the United States today, most private airplanes fly under 24,000 ft. Many have no transponders. Few are under positive control. Military and civil aircraft operate at all flight levels. The space above 24,000 ft presently is under area positive control. All aircraft flying in this area must be equipped with transponders and must file flight plans. Therefore, air traffic controllers know the location of controlled aircraft with respect to all other controlled aircraft in their area. Every aircraft filing a flight plan flies at an assigned altitude on an assigned course. All controlled aircraft are separated by one or more of three criteria. Vertical spacing, time spacing, or horizontal spacing. The present system operates successfully under a highly skilled organization. Control is effective today through a combination of voice communication and radar. The expected increase in air traffic, however, would increase the load that must be absorbed by both pilots and controllers while maintaining voice communication. This would result in radio congestion. Any increase in mixed IFR VFR traffic would only complicate the problem. Bad as the situation on airways might be, it could be much worse over terminal areas in a few more years. Here, aircraft are held through long delays, stacked in holding patterns, or parked on the ground during peak periods of the day. This planned delay is one way to keep current air traffic as safe as it is today. Project Beacon, an FAA task force, was created to study the safe and efficient use of airspace in the years ahead. This project made some recommendations to solve the control problems resulting from continued growth in air traffic. Among the recommendations made were positive control should remain at 24,000 ft mean sea level in and near mountains and be extended down to 14,500 ft elsewhere. On congested airways, positive control should be extended down to 8,000 ft. Project Beacon also called attention to the fact that general-purpose computers should be employed to handle the thousands of additional flight plans that will have to be filed in the future. This would provide basic control information for an increasing number of aircraft flying over the United States. Another important recommendation of Project Beacon was that voice communication between the pilot and controller be drastically reduced. Soon, radio communication channels would become saturated unless some other way could be found to give air traffic controllers altitude and position reports from both military and civil aircraft. The initial reaction to these Project Beacon recommendations was an agreement between the FAA and the Department of Defense, DOD, to utilize a common system. To accomplish this objective, the US national standards were revised to increase the capability of transponders and to ensure the compatibility of military and civil systems. To put those Project Beacon recommendations into effect that would enhance the safety and efficiency of air travel, FAA developed a national airspace system, NAS. DOD's response to meet the national air traffic control objectives was to establish the AIMS program. A stands for air traffic control radar beacon system. I means identification, friend or foe. M represents military equipment. S is for systems. AIMS does not provide a new system in itself. Instead, it expands existing military systems to offer the wider capability of the new civil-military standards. AIMS was organized to make this capability an operational reality for all three military services under a single management. The result of the AIMS management program is twofold. The modification and development of a number of equipments that reduce pilot voice communication with the air traffic controller. And the standardization and reduction of items to decrease the logistics problems that could arise. These new equipments will provide the maximum effective control system technically possible. In today's system, the pilot's transponder and altimeter are not related. The transponder merely reports the position of the aircraft, sometimes more fully identified by its limited code signal. The pilot is the necessary link reporting his altitude to air traffic control. But soon the existing transponder and altimeter can be replaced with new equipment that reports altitude to the pilot and at the same time to the air traffic control system. The new transponder will have an expanded code capability, a maximum of 4096 instead of 64 under mode 3A. Thus, it can report discrete aircraft identity through properly coded electronic messages. All this information, as selected, will appear on an air traffic control scope, reducing the workload that voice communication has previously placed on the controller and the pilot. Alphanumeric characters appearing on the display, associated with the radar blip, will eliminate the need for the shrimp boat. The equipments that accomplish this are gradually being added to all military and air carrier aircraft. When expected peak traffic loads are reached, air traffic control equipments meeting US national standards will be operational in all military and air carrier aircraft. As the cost of these equipments is reduced, they will be used by increasing numbers of private aircraft. Thus, air traffic control systems have progressed from visual sightings and occasional voice contact between aircraft and air traffic controllers to a planned complex system of civil and military facilities involving thousands of men and planes in an immediate continual exchange of necessary information. This information includes identification, azimuth, altitude, range, all made rapidly available to controllers with a drastically reduced requirement for voice communication. Air travel is safe today and will continue to be safe in the busy years ahead. Thanks to the military development of radar as a warning against enemy attack and thanks to years of cooperation between the military and FAA, your safety is assured by the application of radar systems and control techniques to the problems associated with air traffic control. The continuing development of equipment and the close cooperation of the military and the FAA assures that flying for business or pleasure in civil carriers or in private planes as well as military flight will become safer in the future than it ever has been. The challenge of numbers is being met. There will be safety even with increasing numbers of aircraft. Thanks to the efforts of FAA in continuously striving for system efficiency and the AIMS program in managing the military aspects of the system.