AIRWAYS

Aids to navigation are needed over the entire country for general air traffic. In the same way that the Federal government has made hydrographic surveys, constructed lighthouses, marked channels, operated radio stations, and supplied free information to the mariner, it has, upon the development of air navigation, undertaken to develop and maintain lighted and marked airways, to operate a weather service, to broadcast general information, and to furnish free or at cost the charts and other useful information needed by the airman.

Under the terms of the Air Commerce Act, Sec. 5b:

The Secretary of Commerce is authorized to designate and establish civil airways and, within the limits of available appropriations hereafter made by the Congress, (1) to establish, operate, and maintain along such airways all necessary air-navigation facilities except airports. The Secretary of Commerce shall grant no exclusive right for the use of any civil airway, airport, emergency landing field, or other air-navigation facility under his jurisdiction.

The above authorization places the development and maintenance of airways and practically all other aids to navigation under the Bureau of Air Commerce of the Department of Commerce. At the same time the Department of Commerce is given full cooperation by the other departments of the Federal government. For instance, the Hydrographic Office, which is under the Navy Department, furnishes certain charts, tables, and other information which are applicable to both sea and air navigation. The Naval Observatory is in charge of the time service for the entire country, and publishes the Nautical Almanac. The Coast and Geodetic Survey, a branch of the Department of Commerce, publishes certain charts and other tables as explained in Chap. IV.

General Definitions
An airway is an air route between air traffic centers which is over terrain best suited for emergency landings, with landing fields at intervals equipped with aids to air navigation, and a communications system for the transmission of information pertinent to the operation of aircraft. The term airway may apply to any air route for either land planes or seaplanes or both.

A civil airway includes the area of 25 miles around terminal airports and 25 miles each side of center line along the airway together with the air space above the airway. The airway includes the terminal and intermediate airports, emergency landing fields, and all other air-navigation facilities on the airway.

The term navigable air space means air space above the minimum safe altitudes of flight prescribed by proper authority, and such navigable air space shall be subject to a public right of freedom of interstate and foreign air navigation in conformity with the requirements of law.

The term air-navigation facility includes any airport, emergency landing field, light or other signal structure, radio-directional-finding facility, radio or other electrical communication facility, and any other structure or facility, used as an aid to air navigation.

The term airport means any locality, of either water or land, which is adapted for the landing and taking off of aircraft and which provides facilities for shelter, supply, and repair of aircraft; or a place used regularly for receiving or discharging passengers or cargo by air.

The term intermediate or emergency landing field means any locality, of either water or land, which is adapted for the landing and taking off of aircraft, is located along an airway, and is intermediate to airports connected by the airway, but which is not equipped with facilities for shelter, supply, and repair of aircraft and is not used regularly for the receipt or discharge of passengers or cargo by air.
 

Airways
Established airways in the United States [as of 1937] equipped with federal aids to navigation are shown in Fig. 298.

 

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Progress of Civil Aeronautics in the United States
(all statistics are of December 31 of each year)

Item	1926	1931	1936	1937
Scheduled U.S. Air-line Operations, (Foreign and Domestic)
Airplanes on Scheduled air lines	---	590	380	386
Total Mileage	8,404	50,400	61,532	63,656
Express and Freight Carried (lbs)	3,555	1,151,348	8,350,010	8,914,067
Mail Carried (lbs)	810,855	9,643,211	18,324,012	---
Mail Carried (domestic, ton-miles)	---	---	5,741,436	6,698,230
Miles Flown	4,318,087	47,385,987	73,303,836	76,996,163
Passengers Carried	5,782	522,345	1,147,969	1,267,580
Mileage Lighted by Dept of Commerce	2,041	17,512	22,245	22,319
Miscellaneous Flying Operations (All Domestic)
Airplanes in Operation (both licensed & unlicensed)	---	10,090	8,849	10,446
Miles Flown	18,746,640	94,343,115	93,320,375	102,996,355
Passengers Carried	771,010	1,867,517	1,466,058	1,580,412
Total Aiports in Operation	---	2,093	2,342	2,299

The statistics on [in the above chart] will give an idea of the extent to which airways are being used at the present time, together with the progress of scheduled and miscellaneous flying over a period of 10 years.

Facilities provided on a Federal airway include:

1. Rotating beacon lights at approximately 15 mile intervals.
2. Intermediate landing fields so located, relative to airports, that landing areas are available at intervals of approximately 50 miles.
3. Radio-communications stations for weather broadcasts and emergency messages to aircraft.
4. Radio-range beacons for directional guidance.
5. Radio marker beacons for assistance in locating strategic points, such as intermediate landing fields.
6. Weather-reporting service, involving the use of teletypewriter circuits and point-to-point radio. The teletypewriter circuits are used not only for transmission of weather reports and forecasts but also for transmission of reports on progress of aircraft en route along the airways.

 

Operation of the Airways
At all hours of the day and night aircraft speed from city to city with loads of passengers, mail, and express. Darkness no longer holds any terror for the airman; bad weather is a less potent enemy than in former years, because pilots are better equipped to cope with adverse conditions.

The Federal airways system, embracing over 22,000 miles of lighted and radio-equipped air routes, furnishes guidance and assistance to airmen at all times. During daylight hours and in good weather, the aids to air navigation make it easier for the pilot to perform his task efficiently; at night they offer guidance which is even more welcome; and under conditions of poor visibility caused by fog, clouds, rain, or snow, the airway aids are indispensable. Time after time they have enabled aircraft to reach airports or intermediate landing fields safely in circumstances that might have had tragic results if this assistance had been lacking.

 

Airports
As airports throughout the country are established, they are listed and rated after inspection by the Civil Aeronautics Authority. On July 1, 1937, there were 2,361 airports in operation in the United States. However, a great many of these so-called "airports" are not suitable for all-year-round operation.

Complete data on any airport are given in Airway Bulletin 2, which may be obtained upon request to the Civil Aeronautics Authority. A sample extract from Airway Bulletin 2 for Curtiss-Wright Airport, Valley Stream, L. I., N. Y., is show below.

Valley Stream—Curtiss-Wright Airport, auxiliary. One-half mile W.; 16 miles E. of New York City. Lat. 40 40; long. 73 43. Alt. 6 ft. Traingular, sod, level, natural and artificial drainage; three runways, 900 by 112 ft. N./S. and NE./SW., 1,400 by 112 ft. E./W. forming triangle; also an octagonal-shaped asphalt runway 600 by 600 ft. NE. of center with taxi strip to hangar on N.; three landing strips, 3,500 ft. E./W., NW./SE. and NE./SW.; use runways only. CURTISS-WRIGHT VALLEY STREAM on hangar roof. Pole line on N. and NE.; trees around field; lake to E. No servicing. This field for emergency use only.

In addition to landing facilities, the larger airports provide for the pilot: aids for fog and night flying, housing, service, and repair facilities, and, most important of all, weather information.

Air-navigation facilities on civil airways require landing fields approximately 50 miles apart to provide a suitable landing field under conditions of stress of weather or in the event of mechanical difficulties.

 

Intermediate Landing Fields—Where landing fields and airports are non-existent, and where safety demands the establishment of landing facilities, the Federal government establishes and maintains an intermediate field. The intermediate landing fields are occupied by the government under terms of a license providing for the right to carry out construction work incidental to the establishment, preparation, and operation of the landing field, the right of the aeronautical public to use the facilities with rights of ingress and egress and other privileges consistent with the purpose for which the intermediate field is established. The license provides for occupancy for a term of years renewable thereafter on a year-to-year basis. The size of the landing field, grades, conditions of surface, crops, etc., are in accordance with the Department of Commerce’s standard practice and are provided within available appropriations made by Congress for this purpose. The landing field is boundary and obstruction lighted and day marked and provided with an airway beacon and wind indicator.

The standard intermediate field in low altitudes provides two landing strips or runways from 2,600 to 3,000 ft. in length and 400 to 600 ft. wide, approximately at right angles to each other. In the higher altitudes (above 4,000 ft.), the standard length for landing strips is 3,000 to 3,500 ft. Landing strips may form a T, L, or +, and the inner angles at the junctions of the strips are usually beveled off to provide additional diagonal landing space for use in strong cross winds. In many cases it is possible to secure triangular or square fields giving the desired runway lengths in all directions. In rough country, however, it is often possible to secure only one landing strip, in which case an attempt is made to increase the width of such a two-way field sufficiently to permit landing diagonally into strong cross winds.

Intermediate landing fields are marked by a standard marker consisting of a central disk 12 ft. in diameter, concentric with an outer circle 50 ft. in diameter, from the outside of which runway markers 40 ft. long extend in the direction of the runway center lines. On all-way fields the disk is omitted, and a second concentric circle 74 ft. in diameter is installed. The disks, circles, and runway indicators are constructed of crushed rock tamped flush with the surface, or concrete, and whitewashed or sprayed international orange in accordance with the color of the marking scheme of the field.

A wind cone is mounted on a bracket on the side of the airway-beacon tower, showing the direction of the ground wind. At night the wind cone is lighted internally, the light showing through the fabric of the wind cone giving the indication of the direction of the wind.

At night the field is marked with an approved type of airway beacon mounted on a tower sufficiently high to enable the beam of light to clear surrounding obstructions.

The boundary of the field is marked by white lights on low boundary standards, the spacing being about 300 ft. apart. The number of lights is an indication of the size of the field. Daytime boundary markers consist of sheet metal, painted international orange, placed at corners, bends, and along the sides, spaced 300 ft. apart.

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AERONAUTICAL LIGHTING

Night flying is essential for successful air transportation operations in the United States, as the basic source of revenue is the transportation of air mail and express. The civil airways are established under present policies to serve the requirements of the air-mail routes and schedules. The economics of present air transportation requires the gathering of mail at the close of the business day, and transporting it to remote destinations for early delivery on the next or successive business day. Mail collected at the close of the business day on the Pacific Coast will be delivered on the Atlantic Seaboard in the first mail delivery on the next day after posting, the mail having traveled on its journey from coast to coast.

Airways are laid out over the safest low-level routes with bad weather landing fields 50 miles apart, preferably following habitation, roads, communications, and power lines, and adapted for the installation of lighting and radio aids. A high percentage of completed trips on schedule time is essential for the success of air transportation, and the combined use of lights and radio direction is essential to meet this requirement. For safety, the radio-marked airway must coincide with the lighted airways, the pilots making use of all facilities and traveling the same routes in bad weather as on clear nights. When lights are not visible one to another, radio direction takes the pilot over the airway, enabling him to catch a glimpse of lights and fields at close range and this combination of blind-contact flying will greatly increase the flying efficiency and safety.

Basic Principles
The basic principles of aeronautical lighting are the same as those applying to marine lighting, except that different conditions prevail. The airplane travels with great speed through three dimensional spaces over terrain dotted with millions of stray lights. The pilot engaged in flying his airplane has many instruments to watch, and the lights on his course ahead of the airplane are obscured in a large measure by a whirling propeller, pyralin windshield, and his goggles, whereas an officer on the bridge of a steamer devotes substantially all his time to picking up relatively few lights which are identified with the aid of binoculars. On clear nights the airplane may fly high, and the patterns formed by the lights of cities and stray lights serve as aeronautical beacons of first magnitude. But good weather is not always encountered, and low clouds force the pilot to fly low. Under these conditions the stray lights lose their characteristics and become confusing. In the same manner as a steamer sails definite courses from buoy to buoy so as not to run aground, airways marked by beacons and provided with landing fields are laid out following the best terrain to secure the highest possible percentage of flying efficiency and enable safe landings at intermediate fields to be made, in case flying becomes impossible.

Power
It is evident that aeronautical lights must have adequate candlepower which should be in excess of competitive stray lights. Street lights will vary in candlepower from 100 to 5,000 and advertising signs may have candlepower extending from several thousand to several million. In the vicinity of a city a myriad of lights are encountered, illuminating the atmosphere. If aeronautical lights are to be identified by their candlepower, extremely brilliant lights are required. Under such conditions, lights of distinctive color and characteristics are advantageous.

Means of Identification
A distinctive characteristic is required by which an aeronautical light may be identified among the many stray lights. A revolving light is distinctive as compared with fixed lights, but has no individuality. At airports the revolving beacon may be used as an aeronautical light giving the pilot a long-range indication of its aeronautical character, but an auxiliary light is required to flash its individuality by Morse letters or numbers, in order that the particular airport may be identified. About six lights are established to each block of 100 miles and numbers are flashed on the course-light projectors giving the mileage location along the airway.
 

 

This arrangement is shown in Fig. 299 (above). The present practice is to install 24-in. beacons with course lights only on the airports; along the airways, where there are no fields but beacons only, it is the practice to install 36-in. beacons without course lights. Green course lights are used at fields with complete lighting facilities in operation from dusk to dawn. Amber course lights are used at fields where there are lighting facilities that will permit landings, with personnel in attendance who will turn on the lights on request, etc.

Projection
The light should be projected into the air at angles that will render maximum aid to the pilot. For cross-country flying an aeronautical light should preferably be visible all around the horizon and to the zenith. By the use of course lights a projector with 15 degrees beam spread is pointed along the course in each direction and the available light is concentrated into 15 degrees beam spread instead of being dissipated around 360 degrees, thereby increasing the candlepower 24-fold. The proper distribution of light in the vertical plane is of importance.

No advantage of optical apparatus is possible if the light is to show the same candlepower around the horizon and to the zenith. The distribution of light intensities will depend on the spacing of lights along the route. The greatest candlepower from any given beacon should be projected at an angle that will meet the pilot when he is flying above the adjacent beacons. Since the usual height of airway flying is from 500 to 1,500 ft. above the ground, under good weather conditions the elevation of the light in degrees may be calculated. As airplanes often drift off the course, an off-course indication is required, and the 24-in. revolving beacon is used for this purpose in conjunction with the course lights. The Department of Commerce revolving beacon is a very efficient piece of optical apparatus. The light from a 1,000-watt T20 airway lamp is concentrated by a parabolic reflector into a beam of 2,000,000 c.p. having a 4 degrees beam spread. The axis of the beam is elevated to project on an airplane 1,000 ft. above the adjacent beacons. This is accomplished even though the beacon be located on a hill top, valley, or side hill by shimming the base plate of the apparatus to the proper level so that the elevated beam of light makes the proper angle with the slope of the ground. The front-cover glass of the revolving beacon has prisms on the inside surface which deflect some of the light upward from 0 degrees to 25 degrees, so that the pilot will not miss the beam by flying too far above it as he approaches over the airway.

An improvement on the Department of Commerce revolving beacon is a half-drum lens mounted as a saddle on the searchlight drum, gathering the light otherwise lost on the inside of the drum into a fan-shaped beam of light, showing at 90 degrees to the axis of the main beam. As the beacon revolves, showing from the horizon through the zenith to the horizon opposite, secondary flashes of 12,000 c.p. are emitted 2 ½ sec. Before and after the principal flash The zenith light is of considerable aid to the pilot about to land at a landing field or at close range to the beacon, especially in thick weather.

Duration
The luminous period of an aeronautical light is a very important factor, and it should be sufficient to fix the position of the light in the mind of the observer. For marine lights the minimum luminous period found satisfactory is 10 per cent. When the eclipse periods exceed 90 per cent of the cycle time, complaints result. A satisfactory aeronautical light for airports should have a minimum candlepower of 100,000 and a 10 per cent luminous period, according to airport rating regulations. The candlepower may be decreased if the luminous period is increased proportionally, and the same effectiveness is reached up to 50 per cent luminous periods. The opposite condition exists where revolving beacons are used: the candlepower is higher, but the luminous period is less. The course lights used on airway beacons have a luminous period of 35 per cent, which is considered about right.

Light flashes should be of sufficient duration to develop the maximum luminous value upon the retina of the observer’s eye, as the effectiveness of a light is not dependent upon candlepower alone, but upon the duration of the flash, which is a very important factor. It has been proved in marine practice that the full luminous value of a light is reached when the duration of flash is in excess of ¼ sec. With flashing electric lights the time of heating and cooling of lamp filaments must be considered. In code signals the duration of dashes should be three times the duration of dots, and eclipses between dots and dashes should be not less than the duration of the dot. The eclipse between cycles should be in excess of the duration of the dash period. 36-in. beacons are now generally being installed along the routes, and 24-in. beacons on the airports. The older type route beacon used in isolated sections is shown in Fig. 300 (below).
 

 

Characteristics of Lights—There are only two colors sufficiently decided to be used in connection with white for distinguishing lights—red and green, although amber lights are used as airport course lights as previously noted. These colors are distinctive and in general use for buoy lanterns and secondary lights. Of these colors, red is the most distinct. With equal intensity, the red can be seen farther than the white light. If two lights, one red and the other white, appear to be of about equal intensity, the brilliancy of the red light will be greater than that of the white when they are both observed at greater distances; and this effect will be still more marked as the distance from them increases. The white light will become invisible before the other. This phenomenon is especially marked under certain conditions of the atmosphere and is readily understood, since fog generally has a tendency to make a white light appear red; from which it may be inferred that the red rays of the spectrum are transmitted through it more readily than the others. Some heavy fogs allow all the luminous rays to pass equally, and have only the effect of diminishing their intensity; they dim the lights without coloring them.

The colorations produced by the atmosphere are well known. It has been observed that during foggy weather white lights usually become red, green becomes white, and blue lights disappear or change to so pale a violet tint as to be mistaken for white.

Ranges of Lights
The distance at which a light may be seen depends upon its intensity and its heights. We thus have the luminous range and the geographical range. We will examine successively the considerations on which their values are based.

a. Luminous Range - If the lights transmitted their rays through a vacuum the ranges would be proportional to the square roots of their intensities, and it would suffice to know the distance at which a light of a given power could be seen by a person endowed with ordinary vision to determine the range of a light of different intensity.

But, the atmosphere is more or less opaque, which has the effect, in connection with the distance, of weakening the luminous rays, and its action varies between very distant limits. There are fogs so dense that the rays of our most powerful lights can penetrate but a few meters. The ranges, therefore, depend upon the state of the atmosphere, and are actually much less than those which would be deduced from the law just referred to. It is evident, besides, that they also depend upon the acuteness of the observer’s vision.

b. Geographic Range - The distance at which a light may be seen is limited more definitely by the spheroidal form of the earth than by its intensity at the focus. The geographical range depends upon the height of the light above the level of the sea, upon the radius of curvature of that part of the earth’s surface at which it is placed, and upon the amount of atmospheric refraction.

Airway Lighting
All airway beacons should have the same light character with distinctive auxiliary lights for identification purposes. Green auxiliary lights are placed at landing fields and red auxiliary lights at airway beacons, where a landing cannot be effected. On private aeronautical lights on buildings or landmarks, and auxiliary fixed projector of high intensity showing a pencil of light in the direction of the nearest landing field is shown. The red and green lights may be projected along the airway serving as course lights and flashing the mileage number of the beacons along the course. A typical airway beacon is shown in Fig. 301(below).
 

An airway obstruction light is a light indicating an obstruction which is dangerous to air navigation. An airway obstruction light should be red in color, of high candlepower. It should preferably be fixed in character but may be revolving or flashing in special circumstances.

Airport Lighting:
The minimum lighting equipment required on an airport is:

1) Airport beacon with green auxiliary light
2) Landing area flood-light system.
3) Boundary lights.
4) Red obstruction lights.
5) Illuminated wind indicator.
6) Green approach lights on landing runways.
7) Hangar flood lights and roof markings.

An airport location beacon is a beacon light marking an airport location. The light of an airport beacon should be of high intensity and revolving in character, and should have an auxiliary light of distinctive character and green in color. The auxiliary-light characteristics of an airport beacon should establish the identity of the airport from the air.

A landing area flood light is a system of flood-light units for illuminating the surface of an airport to sufficient intensity to effect safe landings of aircraft at night. A landing area flood-light system should illuminate the landing area to an intensity that will reveal details of the landing surface, with depth perception readily possible at 30-ft. altitude and without glare or blinding in landing an airplane.

Boundary lights are lights which outline the entire usable portion of the landing area from the air. Boundary lights should be white or amber in color and fixed in character and arranged so as to mark the landing area distinctively and without confusion with all other lights in the vicinity of the airport.

An airport obstruction light is a light indicating an obstruction which is dangerous to aircraft entering or leaving an airport. An airport obstruction light should be red in color and fixed in character and should mark the height of the obstruction.

An illuminated wind indicator is an illuminated device for indicating the direction of the surface wind. An illuminated wind indicator should show the true indication of the wind at a distance of 1,000 ft. in any direction. The lights should preferably be fixed in character but may be flashing in special circumstances to show wind velocities.

Landing-field approach lights are green lights in the boundary lighting circuit at the end of runways and principal landing strips to indicate the favorable points of approach in landing.

Aircraft Navigation Lights
Aircraft navigation lights are lights carried aboard aircraft flying at night for the purpose of marking aircraft to prevent collision. Between ½ hr. after sunset and ½ hr. before sunrise, airplanes in flight must show the following lights: On the right side, a green light; and on the left side, a red light; each showing unbroken light between two vertical planes whose dihedral angle is 110 degrees when measured to the left and right, respectively, from dead ahead. These lights shall be visible at least 2 miles. At the rear and as far aft as possible, a white light shining rearward, visible in a dihedral angle of 140 degrees bisected by a vertical plane through the line of flight and visible at least 3 miles.

The requirements for airships are the same as for airplanes, excepting the side lights shall be doubled horizontally in a fore-and-aft position and the rear light shall be doubled vertically. Lights in a pair shall be at least 7 ft. apart.

A free balloon, between ½ hr. after sunset and ½ hr. before sunrise, shall display one white light not less than 20 ft. below the car, visible for at lest 2 miles. A fixed balloon, or airship, shall carry three lights—red, white, and red in a vertical line, one over the other, visible at least 2 miles. The top red light shall not be less than 20 ft. below the car, and the lights shall not be less than 7 nor more than 10 ft. apart.

Airplane headlights are high-intensity projectors mounted on the wing tips for use in landing and taxiing at airports. The airplane headlights consist of a streamlined or retractable projector located or built into the wing-tip sections and equipped with parabolic mirror, cover glass, and electric lamp. The usual lamps are 12-volt, 35-amp., G-25 Mogul screw base for horizontal or base-down burning, and average life rated 50 hr. The power supply is a 12-volt battery. The projected light illuminates the path in front of the airplane.

A parachute flare is a pyrotechnic light attached to a parachute for illuminating a large area at night from an altitude for the purpose of selecting a suitable landing field under conditions of emergency and making a landing.

Marking Structures and Obstructions for Air Navigation—The Air Commerce Act provides that:

The persons owning or operating any bridge, causeway, transportation or transmission line, or any structure over navigable waters of the United States shall maintain at their own expense such lights and other signals thereon for the protection of air navigation as the Secretary of Commerce shall prescribe. [Sec. 5 (g).]

Accordingly, the Corps of Engineers, United States Army, issues permits for all structures crossing navigable waters subject to the following conditions:

That if the display of lights and signals on any work hereby authorized by the Corps of Engineers, United States Army, is not otherwise provided for by law, such lights and signals as may be prescribed by the Civil Aeronautics Authority, shall be installed and maintained at the expense of the owner.

The Civil Aeronautics Authority gives detailed instructions for marking obstructions in Form 474.

Radio Aids to Airway Navigation
Radio is of great and increasing value as an aid to navigation along airways. It is used both for direction finding and for communication. These two uses are treated in detail in Chap. XIII on Radio Aids to Navigation.

Weather Service Provided by Bureau of Air Commerce and Weather Bureau
Aeronautical weather information and service for the Nation’s airways are supplied by the United States Weather Bureau and the Civil Aeronautics Authority and disseminated along the Federal airways over more than 12,000 miles of teletypewriter circuits.

Airway weather-reporting stations along the airways report the following information hourly in accordance with scheduled sequences: Name of station, ceiling, sky conditions, visibility and general conditions, wind direction and velocity, temperature, dew point, and barometric pressure. Other information such as unusual field conditions and abnormal weather phenomena, if considered sufficiently serious to affect safety of flight, is included in the report.

At 6-hr. intervals the weather service includes also weather maps and forecasts. The more comprehensive reports required for these purposes are transmitted at 2 a.m., 8 a.m., 2 p.m., and 8 p.m. At these times the information regularly available in sequence reports is given a wider distribution and additional information from many reporting stations away from the airway routes is disseminated.

The weather maps, prepared at important Weather Bureau airport stations on the basis of these comprehensive 6-hr. weather collections, cover the entire United States. Formerly, weather maps were transmitted by teletypewriter from three central points, each of which sent the map for one section of the country. The complete weather maps drawn up at the airport stations contain much more information than the old teletypewriter maps and are more helpful in analyzing weather trends and preparation of forecasts. Copies are made where a definite need for extra copies exists.

The forecasts for airways are drawn up by 10 Weather Bureau forecast centers at Newark, Cleveland, Atlanta, Chicago, Kansas City, Dallas, Salt Lake City, Portland, Oakland, and Burbank, and transmitted over the communications network. Meteorologists at these centers keep a close check on weather conditions within their districts and issue special forecasts between the 6-hr. periods when weather conditions develop so rapidly as to make this necessary.

Navigation along Established Airways
The airways navigation facilities already developed and planned by the government, together with similar private aids, have simplified navigation along established airways. The technique of airway navigation differs from that described in previous chapters and is therefore considered in some detail as the final chapter.

The mission of the air-line operating personnel is to complete with maximum efficiency the greatest possible percentage of scheduled flights with due regard to safety, especially where passengers are involved. The principal airway navigation problems to be solved are those connected with poor visibility, ice, and wind drift. Blind-flying and blind-landing methods previously described have been developed to meet poor visibility conditions due principally to fog. Special de-icers have been fitted on the leading edges of the wings and on propellers to permit flying under ice-forming conditions. The effects of variable winds and load conditions in flight are controlled by setting schedules which permit ample factors of safety in speed and range.

The position, course, and speed of aircraft under these variable conditions are determined by highly developed methods of pilotage, dead reckoning, and radio navigation. For long-range high-altitude flying of future, celestial-navigation methods will doubtless be used. Celestial-navigation methods are already in common use for ocean flying. The principles and general application of pilotage, D.R., radio, and celestial navigation have been covered in previous chapters, and the remainder of this chapter will stress the special methods used on airways.

Flight schedules are controlled by dispatchers who analyze the weather reports, load conditions, and other factors before clearing a plane for flight. Where weather conditions are bad, but flight is possible, the pay load is reduced in order to permit an increased amount of gas so that if it is not possible to land at destination, an alternate clear landing field may be reached.

The following procedure is followed by the most successful air lines:

Before taking off, the navigator makes a careful flight analysis, which is in the nature of a prophecy as to the compass course and air speed necessary to follow schedule. An important item in making the flight analysis is the determination of the estimated time of arrival (E.T.A.). In flight the navigator uses all means at his disposal for the safe navigation of his plane. The best available charts of his route are properly prepared and arranged for convenient use. The charts in common use are the U.S. Department of Commerce sectional and regional charts, and on some special routes, airway strip maps, though the latter are being replaced by the sectional charts. The latest practice is to use two-way radio with a direction finder (D.F.) with rotatable loop in the plane. The D.F. may be used for taking a bearing of any transmitting station within range, or it may be used as a "homing" loop.

Transcontinental and Western Air (TWA) has developed special radio equipment and in addition have produced for their own and public use a series of special radio-navigation charts covering the entire route across the continent, to facilitate the use of radio for position finding. Provisions for taking drift observations are at present inadequate and sorely needed on air lines.

For practical celestial navigation on established airways, more attention must be paid to suitably placed skylights or windows for taking observations. Provision for this can best be done by the original designer. The latest large air-line planes are designed for accomplishing celestial navigation.

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The accompanying forms and explanation of airways navigation are condensed from the navigation data supplied by TWA to each of their pilots. Other air lines use a similar although perhaps a less comprehensive system.

(figure 302)

Figure 302 (above) shows the TWA navigation kit including the necessary data, equipment, and charts for the flight to be covered. The navigation data and forms have been worked out by Peter H. Redpath, navigation engineer, and his force of experts.

 

Figure 303 shows the navigation schedule sheet for Flight No. 1. There are separate sheets for each of 14 or more flights. The schedule times are for elapsed time, block to block. The column "Distance to go" is measured from the approximate mid-point position in adjoining column.
 

(figure 304 Mileage Chart - Columbus to Newark)
 

Figure 304 is the mileage chart for Columbus to Newark. Similar mileage charts are available for all flights. The Flight Plan (Fig. 305) is filled out by the pilot before taking off. It will be noted that the form is so prepared as to reduce to a minimum the labor of completing the form. Detailed instructions for completing the forms, with sample problems, are furnished each pilot. Abbreviations are used where possible.
 

(figure 306 - Pilot's Navigational Log Sheet)
 

The actual conditions encountered on the flight are carefully recorded on the Pilot’s Navigational Log Sheet Fig. 306 (above).

Both the flight plan and the pilot’s navigational log sheet are analyzed and filed in the office of the navigation engineer at Kansas City. Experienced pilots submit flight plans which compare very closely with the log sheet.

This information originally appeared in a 1937 publication

2003 Wings Publishing