INSTRUMENT AND RADIO FLYING
By: E. A. Cutrell
Few men are as well qualified to speak on instrument flying as is the author of this
article. Out of his long experience as a member of the Department of Commerce
piloting staff engaged in blind landing research, as instructor in instrument flying for
American Airlines, Mr. Cutrell outlines certain practices which he has found useful in
instrument flight training and radio beam flying, and discusses some of the faults and
difficulties which are commonly encountered.
If you are a pilot and wish to become competent in the type of flying required for
S.A.T. rating, your entire training in instrument and radio navigation should be planned
along lines that will best qualify you to meet all conditions with which you will be faced
in getting through the three hundred and sixty-five different kinds of weather to be found
the year around. With all the facilities, aids and improvements developed since 1922 you
must realize first that there are still very definite limitations as to the weather
conditions that even the most qualified pilots can go through safely. The two most
important limiting factors at this time are "icing conditions" and
"visibility conditions at destination." De-icing or ice-preventing auxiliaries
are still in the development stages, and facilities to approach for landing safely under
conditions of low ceiling and poor visibility must still be classed as experimental. The
technique obtained in your training is only the foundation on which you may build (by long
practice) your knowledge and experience for safety in handling the problems of all-weather
flying.
When first taking the controls under a hood, use the so-called 1-2-3- system, controlling the airplane about its three axes by means of the turn, bank, and rate of climb indicators. The 1-2-3 system, as outlined in Stark’s book on blind flying, constitutes learning to control the airplane by correcting the three instruments one at a time, in the order given, until it becomes natural or mechanical to coordinate them. For example, if the turn indicator hand is off center, correct it with the rudder until you get it centered, regardless of the amount of pressure necessary on the pedal. With the turn indicator in the center, next fix your attention on the ball of the bank indicator and bring it to center with the ailerons, then move your attention to the climb indicator and bring the hand to zero with the elevators. Finally, go back to the turn indicator and repeat the process in rotation as before.
During this practice, rely completely on the indications of the instruments and disregard you sense of balance or feeling as to the position of the airplane. At times, you will suspect that you are leaning to one side or the other and may have some doubts about the correctness of the functioning of the instruments, but remember that you have nothing else to go by and must accept their indications completely.
When it becomes easy to keep all the instruments centered, try the same system for gentle turns. Instead of keeping the turn indicator in the center, keep it off on the right side just the width of the hand. This time you will be making a gentle bank of about 15 deg. You may experience difficulty in keeping the turn indicator from increasing its off-center position. If so, use sufficient opposite pressure on the rudder pedal to return it to the desired position. Sometimes it will seem necessary to use an undue amount of rudder to gain this end. If, at any time, the airplane gets into a position that seems strange and you have trouble centering the instruments, go back to the 1-2-3 system by first centering the turn hand with rudder, the ball with ailerons, then rate of climb with the elevators.
In a short time you will find that by the 1-2-3 system you have learned to coordinate your ailerons and rudder so that in centering the turn indicator and ball you are at times correcting the ball with the rudder and centering the turn with the ailerons. This is perfectly correct and natural and means that you have acquired a natural "feel" with the instruments and are able to co-ordinate your controls by watching them. If you find that you are not co-ordinating the bank and turn indications, practice correcting the ball with the rudder by bearing on the left rudder when the ball is off center to the left, the right rudder when the ball is off to the right, and at the same time hold the turn hand in the center with the ailerons. Bear in mind that it is always necessary to go back to the 1-2-3 system whenever the airplane gets in an abnormal or unknown attitude.
Flying blind by compass
The next step is to learn to fly a compass course. Glance at your compass two or three
times and determine the approximate reading. Turn either to an east or west heading by
moving the turn indicator either to the left or right just the width of the hand. The
compass will oscillate so that when attempting to keep it on an east or west heading it
will be necessary to take the mean of the oscillations as the reading. Practice until you
are able to follow a comparatively straight course.
Next, from either an east or west heading, place the turn indicator hand one width from the center position and hold for one minute. Then return to center position and check your compass heading to determine whether or not the turn had was off center too much or too little to complete a 180-deg. turn in one minute. Continue making these turns until you are able to determine the proper position for the turn hand both to the right and left side to complete 180-deg. turns in one minute within a limit of 15-deg. error.
The next step is to practice flying at various engine speeds to obtain different air speeds in level flight, in glides of different rates of descent, and in climbs. In each of these conditions learn to adjust the stabilizer and throttle so that it will become just as natural to change them while flying by instrument as at any other time.
Practice making steep banks over 45 deg. and recovering to normal flight position. Practice recovering from stalls, spirals, tailspins and unusual maneuvers to feel confident that the airplane can easily be righted from any unknown attitude.
Except when intentionally climbing or losing altitude, make all your practice flights at some constant altitude and try to maintain it within plus or minus 100 ft. This practice will develop a habit of using the altimeter mechanically as one of the flight instruments instead of using it merely as a check on your height above the earth. This will become very important when flying near the ground, or for making landing approaches.
Familiarity with radio
Before attempting to fly the radio range beams, thoroughly memorize and fix definitely
in mind the "N" and "A" quadrants of the radio range station in the
vicinity of which you are flying. Learn the magnetic beam courses of this range station
within the nearest five degrees, indicated by graduation marks on the compass or
directional gyro. The quadrants and courses, particularly the courses of the beam on which
an approach to the airport is made, should be so thoroughly memorized that the complete
laye proper tone is meant a
moderate normal signal intensity for your ears. In case your volume control skips from a
loud to low tone so that close adjustment is difficult, advantage can be taken of the
tuning dial to reduce the tone to some extent when necessary although the volume control
method is preferable.
The principal reasons for maintaining a normal volume are:
(out of the range station can be instantly visualized without reference to a chart. Next learn the schedules on which regular weather broadcasts are made so that your radio problems can be worked between broadcast periods.
When flying a beam, the volume of the received signals should be maintained constant by use of the volume control. It should become a habit when following a beam to keep the volume adjusted to the proper tone at all times. By tha) by becoming accustomed to one volume of signal you are able to estimate, by the rate of increase, the approximate distance from the range station;
(b) you are more able to tell, by the strength of the "N" and "A" identification signals in relation to your approximate distance from the station, about how far you are from the on-course of the beam;
(c) you train your ears to detect more certainly the cone of silence and the following build-up of signal;
(d) you can more readily prove that you have crossed the station by the subsequent fading signal;
(e) you can distinguish more easily the increase, fade or twilight zone in working an orientation problem.
Orientation—volume method
One of the most difficult radio problems has been orientation from an unknown position
in the vicinity of a radio range station. In working the volume-of-signal method of
orientation the only beam course or flight courses necessary to remember are the inbound
and outbound courses of the leg which you expect to follow into the radio range station to
make an approach down to the airport. This will be referred to as the approach beam. The
general layout of the beams, however, and their relation to the vicinity of the airport
should be thoroughly memorized. A few simple instructions for practicing orientation by
the volume-of-signal method follow. If your position in relation to the radio range
station is unknown, turn to the outbound gyro or compass course of the approach beam. Turn
the volume control down slightly less than the proper tone for your ears. Be careful not
to adjust the volume again until you are certain that the signal is increasing or fading.
Also avoid touching the earphones or electrical switches for that might vary the intensity
of signal. Continue flying the straight course until the volume of signal becomes quite
noticeably lower. You are then assured that the radio range station is behind you, and by
either the "N" or "A" signal you know in which direction to turn to
pick up the approach beam. If the signal increases, your course can be continued until you
have passed beyond the range station sufficiently far to know that you are in either the
"N" or "A" quadrant that bounds the approach beam. Then you turn in
the direction as indicated by the signal, until arriving at the twilight zone when you
will assume the inbound course of the beam, determine your gyro heading and follow to the
cone of silence over the station.
(figure 1)
A typical radio range station chart showing the first method of approach by volume-of-signal orientation. These courses 150, 330, and 70, 250 are satisfactory for giving a picture of the layout of the Chicago range. The actual true courses are 152, 332, and 68, 248.
Another method
An alternate procedure for solving the volume of signal orientation is illustrated in
Fig. 1. After turning to the outbound course of the approach beam as outlined above, turn
the volume down to a moderate tone and listen for the quadrant signal. If an
"N," turn to a course 30 deg. away from the outbound approach beam course into
the "N" quadrant. If an "A," turn 30 deg. away from this course into
the "A" quadrant. Continue to fly this heading without changing the volume
control until you have a definite indication that the signal is decreasing, increasing or
that you are approaching or crossing a beam. In finding your position by this method there
is no necessity for a quick decision as to whether the signal is increasing or fading
since you are flying in a direction which will not take you far from the beam on which you
wish to return to the radio station. Also, as there is no need to make a quick turn or
change of course, after you are on the proper heading, you may give all your attention to
the signal to which you are listening.
After you have flown the course chosen for sufficient time you will find one of three conditions taking place:
(a) the signal will be fading,
(b) it will be increasing, or
(c) you will be flying in the twilight zone of a beam.
If the signal is unmistakably fading you have positively identified the quadrant, therefore turn directly to the beam, assuming its course as you approach the on-course signal. Establish the gyro course of the beam and complete your approach to the station (Fig. 1 B B’ B"). If the signal is unmistakably increasing, continue on your course until you cross a beam whereupon turn to the outbound course of the approach beam (Fig. 1 A A’). When there is an indication that the signal is then decreasing, turn in the proper direction to get on the beam. It is then advisable to follow the beam going away from the station until far enough out to make the proper reverse turn to come back in. If you are approaching or crossing a beam after first starting the problem, turn immediately to the course of the approach beam as outlined above (Fig. 1 A"). This method of orientation is positive and requires but little remembering of courses or solving of problems to determine quadrants or beams. Important points to bear in mind: The course (within nearest 5 deg. of beam) on which you wish to fly to range station; the proper setting of volume control; the continuing straight course; how to distinguish increase, fade, or twilight zone of beam.
(figure 2)
The second volume-of-signal method of approach showing flight paths for the three different sets of conditions outlined.
Except in orientation, always follow the beam going away from the range if you are to make an approach over the station rather than to fly out in the quadrant and then turn back and get on the beam. Check your gyro course going out (Fig. 2). Ordinarily the distance should be at least 8 miles. To come back, turn from the on-course signal 30 deg. to the leeward of the outbound gyro course of the beam and hold for 45 seconds. A normal 210-deg. turn toward the beam will then put you back approximately on the beam. The wind direction and velocity should be kept in mind at all times. Always check your clock for the next broadcast before turning to come in on a beam.
Following a beam
A beam should be flown as a gyro or compass course with the radio signals used to
determine the course. Many pilots in preliminary attempts to fly a beam by the turn
indicator and compass endeavored to follow the on-course signal by a succession of abrupt
corrections, first from the "N" side then to the "A." The gyro course
of the beam should be determined by making corrections smoothly and deliberately but at
the same time in a positive manner. It is good technique to fly the beam with too few
rather than too many corrections. The first correction as shown in Fig. 3 should be not
less than 20 deg. Each correction should be definitely held until an on-course signal is
received and then the gyro returned to the course of the beam. The second correction
should be 10 deg. and additional corrections 5 deg. Practice will enable you to limit
corrections to 2 ½ deg. upon reaching the last 2 or 3 miles from the range station. The
most common mistake in flying a beam is to over-correct the course, particularly nearing
the station (Fig. 3).
(figure 3)
Method of establishing gyro compass course from radio range beam showing how to make final corrections during the last 2 or 3 miles of the approach.
Crossing the silence cone
Whenever you use the cone of silence as a fix to begin to let down, always prove that
you have crossed the range station by listening for the fade away of the built-up signal.
Due to mountains, swinging of the beam, or a faulty receiver, the radio signals sometimes
fade, producing an effect somewhat similar to a cone of silence. It is therefore always
important to check the signal volume immediately after crossing the station. This may be
done after the glide is started before losing altitude below a safe limit. This decrease
of signal will usually be very definite in a glide within 4,000 ft. after passing the
station.
The safest approach to an airport from the range station is in a glide on a straight course ahead. Knowing the gyro course following the beam to the station you can lose the necessary altitude by continuing on the same heading after crossing the station. The opposite beam can be checked by making the same gentle corrections as when approaching the station (where the beam crosses the airport).
The glide should be made under power, with wheels and flaps down at the normal gliding speed and rate of descent of not over 500 ft. a minute. The proper throttle positions should be set after crossing the station so that they need not be changed until the minimum safe altitude is reached.
Navigation notes
When flying blind, or over the top, obtain all available information regarding weather
conditions, wind directions and velocities before departure and while en route. If
practicable, after taking off check compass against known ground courses by land marks. En
route, take advantage of every possible check of your course and location. It is important
(due to characteristics of radio range stations) that a log of your compass course be kept
when flying without visible reference to the ground between any two radio range stations
or other points where your definite position can be determined. Even when flying the beam
between two stations, a positive compass course, or a series of compass courses averaged,
should be noted while checking on the radio range signals. Do not pass up any range
station, beam intersection from an off-course station, marker, or ground station, that
might identify your position. Check on each. Compare your speed vs. distance against those
calculated. In approaching a range station from an open quadrant, or if checking in on the
leg of a beam where there may be a possibility of intercepting either of two beams, always
make a check by turning to the course of one beam and follow it far enough to positively
identify it.
