Crowded Skyways CONGESTION PROBLEMS TEST AIR TRAFFIC CONTROLLERS

Press, Volume CIII, Issue 30603, 20 November 1964, Page 12

Crowded Skyways CONGESTION PROBLEMS TEST AIR TRAFFIC CONTROLLERS

IBy

J. C. H. Roberts,

in the "Yorkshire Post"}

(Reprinted bp arrangement >

Your seat-belt is fastened, the powerful turbo-jets start to roar. With the vast open sky above there seems to be no problems of trafiic congestion in the air. This is just an illusion. Parts of this wide and seemingly empty sky are often so full of fast flying aircraft that pilots and air trafiic controllers justifiably complain of inadequate airways.

Probably the most congested region is over the North Atlantic, while the area over the Strait of Dover is becoming equally saturated. Other areas, too, are approaching danger point. The speed of jet aircraft has shrunk the enormous air space over the North Atlantic to such an extent that only 20 aircraft an hour can be allowed to use its 1800 miles long, 500 miles wide and two miles thick “jet-way.” On busy days faster flying subsonic jets have to be deliberately delayed so as to ensure the safety of those already airborne. A Dangerous Strait The Strait of Dover, with its tiny 40 by 80 mile area, with a ceiling of 4500 ft, is acutely dangerous because privately owned aircraft, many of them without adequate means of radio communication, confuse traffic controllers and airline pilots by deserting their designated air corridors. At present there is no law to prevent a private plane changing its course in this busy area, but their divergencies create confusion and endanger the safety of the 900 aircraft which use this airspace daily. Civil and military flights must be safely separated, for neither can claim unrestricted and exclusive use of airspace. The problem of air traffic control begins on the ground. It also starts on the ramp, not on the runway. Immediately an aircraft’s powerful engines roar into life precious fuel is consumed. If take-off is delayed, fuel shortage occurs, and this may be so critical that drastic alterations to the altitude, routing and timing of the aircraft may have to be made. Adequate Separation Take-offs and landings must be carefully regulated to ensure adequate separation between flights. Each plane has to be allowed a “cocoon” of safe air 160 miles long, 120 miles wide, and nearly half a mile thick to avoid collision dangers. Obviously there is a limit Ito the number of cocoons to accommodate aircraft. To control separation and flow, traffic controllers can ask pilots to travel at certain speeds, or to lengthen their flight paths so that they travel at a longer route and

take more time. They can also be instructed to hold a position by flying a tight pattern over a given area. Often as many as 20 aircraft may be “stacked” over such an area, each descending 1000 ft to the next lowest cleared altitude as the bottom aircraft is cleared to land. To complicate matters departure and arrival times must be carefully regulated to conform with noise abatement and other local regulations. Most commercial jet aircraft traverse the last 10 miles at a speed of 120 knots so as to ensure a precisely controlled rate of descent and lateral correction to line the aircraft up with the runway. Any variation in velocity can affect the spacing between leading and following air-

craft. Thus if a plane is 19 seconds late in landing because of wind changes or engine trouble, the aircraft behind may be more than half a mile closer. If a plane misses its final approach, as sometimes happens in bad weather, and has to circuit the airport, the controller must jockey it through terminal area traffic until it is in a position to enter the approach pattern in a satisfactory sequence. Economical Levels Another factor which has contributed to the present overcrowding of world air routes, especially those over the North Atlantic, is the competition between commercial air lines. Each strives for assignment to the most economical (fuel saving) upper levels of the narrow “jetway” between 28,000 and 41,000 ft. But weather conditions cannot be controlled, and often flights can only be made when weather conditions are favourable. These factors, however, appear relatively insignificant when compared with

the fact that in an age of advanced technology, longdistance en route navigation is still so imprecise that neither air traffic controllers nor pilots can always be sure of an aircraft’s real position. Once an aircraft commences its take-off it becomes part of a vast man-machine system that is so complex and dynamic that nobody can be positively sure how an action in one part of the system may affect another part. How to use the world’s air-space efficiently is part of the complex problem facing air traffic system designers today. Pilot’s Ability It involves not only the precision with which an aircraft s position can be fixed and continuously monitored, but also the ability of the pilot and his navigational equipment to stay within the confines of his safety “cocoon.” Often, as in the case of the cramped, muni-cipally-owned airports, the solution is outside the designer’s jurisdiction. Though computers may be used in the future to calculate take-offs and landings, at the present time, long-distance air navigation relies on dead reckoning, in which the aircraft’s navigator estimates the aircraft’s position by continually observing its speed and direction of travel from a known starting point. The more reliable “Doppler” navigation and inertial guidance equipment used successfully in military aircraft and space vehicles, is either too bulky, too costly or too complex for commercial use. Modern radar equipment is not foolproof. When the blip of an aircraft “blooms" on the radar scope, it sometimes covers a scale of three miles. As a result controllers are uncertain of the exact position of an aircraft even though it can be seen on radar. Similar problems are encountered when aircraft arc “stacked" in holding positions and individual aircraft blips shadow each other when their respective aircraft are on the same track but at different altitudes. When there are more than 100 aircraft within 40 miles radius of the control tower, the controller has often to ask a particular craft to identify itself by making a procedural turn which he can see on the scope. Although most of the United States and much of Britain and Europe is well covered by radar, some of the equipment used in en-route air traffic control service is of the out-dated World War II naval type. Thus some highaltitude flights fade out in a “black hole” above the antenna or between 20 and 30 miles away, or disappear in rain squalls and thunderstorms. Altantic “Black Hole” Even in the middle of the Atlantic there is a “black hole” which is untouched by the radar sweeps from either side, and where control of aircraft may falter. In the United States, where acute congestion in the air was publicly recognised after a series of spectacular midair collisions, plan after plan for improving the present system has been suggested by a ceaseless round of study groups. In Britain, the Ministry of Aviation has embarked on a much needed study relating to the application of automation. In Europe, where national boundaries have long been overrun by jets in a matter of minutes, and where the approach lights at the end of a runway can glow brightly on the soil of a neighbouring country, new traffic control systems are still only at the planning stage. Over the congested North Atlantic “jet-ways,” agreements about procedural and technological improvements among the member nations of the International Civil Aviation Organisation, are ratified only after political negotiations, and adherence is still a problem. Often technically valid solutions are subordinated to politics and economics. Far too many research and development projects are smothered by changes in administration or alterations in policy before they can be brought to fruition. Although the danger of commercially exploiting supersonic aircraft without first effecting considerable improvements in existing air traffic control systems is self-apparent, the rate of progress in the development of faster aircraft has considerably outpaced the development of the more essential air traffic control equipment.

The open sky is an illusion. Some routes are so full of fast flying aircraft that congestion is approaching danger point. In the “Yorkshire Post” an engineering consultant discusses the problems of controlling flights.