NOTE: The instrument maneuvers presented in Chapter V are based on an airplane equipped with a turn coordinator. If the airplane flown has a turn needle, the descriptions apply if "turn needle" is substituted for "miniature aircraft of the turn coordinator."
Attitude instrument flying may be defined in general terms as the control of an airplane's spatial position by the use of instruments rather than by outside visual reference.
Any flight, regardless of the airplane used or route flown, consists of basic maneuvers. In visual flight, you control airplane attitude with relation to the natural horizon by using certain reference points on the airplane. In instrument flight, you control airplane attitude by reference to the flight instruments. A proper interpretation of the flight instruments will give you essentially the same information that outside references do in visual flight. Once you learn the role of all instruments in establishing and maintaining a desired airplane attitude, you are better equipped to control the airplane in emergency situations involving failure of one or more key instruments.
There are at least two basic methods in use for learning attitude instrument flying. Both methods involve the use of the same instruments, and both use the same responses for attitude control. They differ in their reliance on the attitude indicator and consequently on the use and interpretation of other instruments.
One method presents the problem of attitude control essentially from this standpoint: airplane performance depends upon how you control the attitude and thrust relationship of the airplane. The first group of instruments presents existing performance information. The altimeter, for example, shows the altitude, or altitude changes, resulting from power and attitude control. The airspeed indicator, vertical-speed indicator, heading indicator, and turn coordinator likewise tell you what the airplane is doing with respect to speed, vertical movement, direction, rate of direction change and trim. This group of instruments is therefore referred to as the performance instruments.
The second group of instruments presents information necessary to determine the power and attitude necessary for maintaining or changing airplane performance. The attitude indicator and tachometer (or manifold pressure gauge and tachometer in combination) show you what pitch, bank, and power combination is controlling the performance shown on the other instruments. These are called control instruments.
The third group shows you where your flight path is with respect to the earth's surface, and therefore these are called navigation instruments.
Another basic method for presenting attitude instrument flying, groups the instruments as they relate to control function as well as airplane performance. All maneuvers involve some degree of motion about the lateral (pitch), longitudinal (bank/roll), and vertical (yaw) axes. Attitude control is accordingly stressed in this handbook in terms of pitch control, bank control, power control, and trim control (Fig. 5-1). Instruments are therefore grouped as they relate to control function and airplane performance as follows:
Pitch Instruments
Attitude Indicator
Altimeter
Airspeed Indicator
Vertical-Speed Indicator
Bank Instruments
Attitude Indicator
Heading Indicator
Turn Coordinator
Power Instruments
Manifold Pressure Gauge (MP)
Tachometer/RPM
Airspeed Indicator
Engine Pressure Ratio (EPR) - Jet
Figure 5-1. Attitude control.
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For any maneuver or condition of flight, the pitch, bank, and power control requirements are most clearly indicated by certain key instruments. Those instrument which provide the most pertinent and essential information will be referred to as primary instruments. Supporting instruments back up and supplement the information shown on the primary instruments. Straight-and-level flight at a constant airspeed, for example, means that an exact altitude is to be maintained with zero bank (constant heading) at a constant airspeed. The pitch instrument, bank instrument, and power instrument which tell you whether you are maintaining this flight condition are the:
1. Altimeter - which supplies the most pertinent altitude information
and is therefore primary for pitch.
2. Heading Indicator - which supplies the most pertinent bank
or heading information ("banking" means turning) and is therefore primary
for bank.
3. Airspeed Indicator - which supplies the most pertinent information
concerning performance in level flight in terms of power output, and is
therefore primary for power.
This concept of primary and supporting instruments in no way lessens the value of any particular flight instrument. The attitude indicator is the basic attitude reference. It is the only instrument which portrays instantly and directly the actual flight attitude. It should always be used, when available, in establishing and maintaining pitch and bank attitudes. The specific use of primary and supporting instruments will be better understood as the basic instrument maneuvers are presented in detail.
You will find the terms "direct indicating instrument" and "indirect indicating instrument" used in the following pages. A "direct" indication is the true and instantaneous reflection of airplane pitch and bank attitude by the miniature aircraft relative to the horizon bar of the attitude indicator. The altimeter, airspeed indicator, and vertical-speed indicator give "indirect" indications of pitch attitude at a given power setting. The heading indicator and turn needle give "indirect" indications of bank attitude.
Included in the appendix of this handbook is a reproduction of the Instrument Flight Instructor Lesson Guide (Airplanes) which is correlated with the material which follows.
Fundamental Skills
During attitude instrument training, you must develop three fundamental skills involved in all instrument flight maneuvers: instrument cross-check, instrument interpretation, and aircraft control. Although you learn these skills separately and in deliberate sequence, a measure of your proficiency in precision flying will be your ability to integrate these skills into unified, smooth, positive control responses to maintain any prescribed flight path.
Cross-Check.
The first fundamental skill is cross-checking (also called "scanning" or "instrument coverage"). Cross-checking is the continuous and logical observation of instruments for attitude and performance information. In attitude instrument flying, the pilot maintains an attitude by reference to instruments that will produce the desired result in performance. Due to human error, instrument error, and airplane performance differences in various atmospheric and loading conditions, it is impossible to establish an attitude and have performance remain constant for a long period of time. These variables make it necessary for the pilot to constantly check the instruments and make appropriate changes in airplane attitude.
As a beginner, you may cross-check rapidly, looking at the instruments without knowing exactly what you are looking for. With increasing experience in basic instrument maneuvers and familiarity with the instrument indications associated with them, you will learn what to look for, when to look for it, and what response to make. As proficiency increases, you scan primarily from habit, suiting your scanning rate and sequence to the demands of the flight situation. You can expect to make many of the common scanning errors, both during training and at any subsequent time, if you fail to maintain basic instrument proficiency through practice.
The following cross-check faults are frequent problems:
1. Fixation, or staring at a single instrument, usually occurs for a good reason, but with poor results. For instance, you may find yourself staring at your altimeter which reads 200 feet below assigned altitude, wondering how the needle got there. While you gaze at the instrument, perhaps with increasing tension on the controls, a heading change occurs unnoticed, and more errors accumulate.
Another common fixation is likely when you initiate an attitude change. For example, you establish a shallow bank for a 90° turn and stare at the heading indicator throughout the turn, instead of maintaining your cross-check of other pertinent instruments. You know that the aircraft is turning and that you need not recheck the heading indicator for approximately 25 seconds after turn entry, yet you can't take your eyes off the instrument. The problem here may not be entirely due to cross-check error. It may be related to difficulties with one or both of the other fundamental skills. You may be fixating because of uncertainty about reading the heading indicator (interpretation ) or because of inconsistency in rolling out of turns (control).
2. Omission of an instrument from your cross-check is another likely fault. It may be caused by failure to anticipate significant instrument indications following attitude changes. For example, on your roll out from a 180° steep turn, you establish straight and level flight with reference to the attitude indicator alone, neglecting to check the heading indicator for constant heading information. Because of precession error, the attitude indicator will temporarily show a slight error, correctable by quick reference to the other flight instruments.
3. Emphasis on a single instrument, instead of on the combination of instruments necessary for attitude information, is an understandable fault during initial stages of training. You naturally tend to rely on the instrument that you understand most readily, even when it provides erroneous or inadequate information. Until completely accurate and infallible instruments are devised, reliance on a single instrument is poor technique. For example, you can maintain reasonably close altitude control with the attitude indicator, but you cannot hold altitude with precision without including the altimeter in your cross-check.