Indicated airspeed (IAS)—the airspeed that is shown on the airspeed indicator. See Figure 3-1.

Figure 3-1. Airspeed indicator
Calibrated airspeed (CAS)—the indicated airspeed corrected for position or installation error.
Equivalent airspeed (EAS)—calibrated airspeed corrected for compressibility. EAS will always be lower than CAS.
True airspeed (TAS)—the equivalent airspeed corrected for temperature and pressure altitude. At speeds below 200 knots, TAS can be found by correcting CAS for temperature and pressure altitude. A rule of thumb is that TAS is 2 percent more than CAS per 1,000 feet of altitude above sea level.
Mach number—the ratio of aircraft true airspeed to the speed of sound.
Indicated altitude—the altitude above mean sea level indicated on an altimeter that is set to the current local altimeter setting. Better vertical separation of aircraft in a particular area results when all pilots use the local altimeter setting.
Pressure altitude—the altitude indicated on an altimeter when it is set to the standard sea level pressure of 29.92 inches of mercury ("Hg). Above 18,000 feet MSL, flight levels, which are pressure altitudes, are flown.
Density altitude—the result of a given pressure altitude that is corrected for a nonstandard temperature.
True altitude—the exact height above sea level. The altimeter setting yields true altitude at field elevation.
Pressure decreases with altitude most rapidly in cold air and least rapidly in warm air. However, the standard pressure lapse rate is a decrease of 1 "Hg for each 1,000 feet of increase in altitude. See Figures 3-2 and 3-3.

Figure 3-2

Figure 3-3
Before departure, the pilot should obtain the altimeter setting given for the local airport. En route, the pilot should set the altimeter to the closest station within 100 NM. The pilot will be periodically advised by ATC of the proper altimeter setting.
At or above 18,000 feet, all aircraft use 29.92 "Hg. The change to or from 29.92 "Hg should be made when passing through 18,000 feet. If this change is not made, the altimeter will read erroneously.
Aside from incorrectly setting an altimeter, one of the most common errors is to misread it. The small hand indicates thousand of feet. The long, thin hand indicates hundreds of feet. The very thin hand with the triangular tip indicates tens of thousand of feet. See Figure 3-4.

Figure 3-4. Altimeter
To preflight the altimeter, the current reported altimeter setting should be set in the Kollsman window. Note any variation between the known field elevation and the altimeter indication. If the variation exceeds ±75 feet, the accuracy of the altimeter is questionable and the problem should be referred to an appropriately rated repair station for evaluation and possible correction.
The vertical speed indicator (VSI) is designed to indicate the rate of climb or descent. Although not required by regulation to be on board, it is commonly found on instrument airplanes. A VSI pre-takeoff check is made to check for a “zero” reading. If it is indicating a climb or descent, note the error and apply it to readings in flight. See Figure 3-5.

Figure 3-5. Vertical speed indicator (VSI)
Gyroscopes (gyros) exhibit two important principles: rigidity in space and precession. There are three instruments controlled by gyroscopes: attitude indicator, turn coordinator, and the heading indicator.
The attitude indicator provides an immediate, direct, and corresponding indication of any change of aircraft pitch and bank attitude in relation to the natural horizon. It is the pilot’s primary instrument during transitions of pitch or bank attitudes. See Figure 3-6.

Figure 3-6. Attitude indicator
The attitude indicator exhibits several inherent errors:
An attitude indicator pre-takeoff check verifies that the horizon bar stabilizes within five minutes, and does not dip more than 5° during taxiing turns.
The turn coordinator is a gyroscopically operated instrument that is designed to show roll rate, rate of turn, and quality of turn. It acts as a backup system in case of a failure of the vacuum powered attitude indicator. See Figure 3-7.

Figure 3-7. Turn coordinator
Before starting the engine, the turn needle should be centered and the race full of fluid. During a taxiing turn, the needle will indicate a turn in the proper direction and the ball will show a skid.
An airplane turns because of the horizontal component of lift in a banked attitude. The greater the horizontal lift at any airspeed, the greater the rate of turn. The angle of attack must be increased to maintain altitude during a turn because the vertical component of lift decreases as a result of the bank. When airspeed is decreased in a turn, either a decrease in the bank angle or an increase in the angle of attack is required to maintain level flight. During a constant bank level turn, an increase in airspeed would result in a decrease in rate of turn and an increase in turn radius.
In a coordinated turn, horizontal lift and centrifugal force are equal. In a skid, the rate of turn is too great for the angle of bank, and excessive centrifugal force causes the ball to move to the outside of the turn. To correct to coordinated flight, the pilot should increase the bank or decrease the rate of turn, or a combination of both. In a slip, the rate of turn is too slow for the angle of bank, and the lack of centrifugal force causes the ball to move to the inside of the turn. To return to coordinated flight, the pilot needs to decrease the bank or increase the rate of turn, or a combination of both.
A standard rate turn (3° per second) takes 2 minutes to complete a 360° turn. A half-standard rate turn (1.5° per second) takes 4 minutes to complete a 360° turn.
The heading indicator is a gyroscopically operated instrument. Its purpose is to indicate the aircraft’s heading without the errors that are inherent in the magnetic compass. See Figure 3-8. Due to precessional error, however, the heading indicator should be regularly compared to the magnetic compass in flight.
The heading indicator pre-takeoff check is made by setting it and checking for proper alignment after making taxiing turns.

Figure 3-8. Heading indicator
The magnetic compass is the only self-contained directional instrument in the aircraft. It is influenced by magnetic dip which causes northerly turning error and acceleration/deceleration error.
When northerly turning error occurs, the compass will lag behind the actual aircraft heading while turning through headings in the northern half of the compass rose, and lead the aircraft’s actual heading in the southern half. The error is most pronounced when turning through north or south, and is approximately equal in degrees to the latitude. See Figure 3-9.

Figure 3-9
The acceleration/deceleration error is most pronounced on headings of east and west. When accelerating, the compass indicates a turn toward the north, and when decelerating it indicates a turn toward the south. The acronym ANDS is a good memory aid:
A magnetic compass pre-takeoff check verifies that:
Electronic flight instrument systems integrate many individual instruments into a single presentation called a primary flight display (PFD). Flight instrument presentations on a PFD differ from conventional instrumentation not only in format, but sometimes in location as well. For example, the attitude indicator on the PFD is often larger than conventional round-dial presentations of an artificial horizon. Airspeed and altitude indications are presented on vertical tape displays that appear on the left and right sides of the primary flight display. The vertical speed indicator is depicted using conventional analog presentation. Turn coordination is shown using a segmented triangle near the top of the attitude indicator. The rate-of-turn indicator appears as a curved line display at the top of the heading/navigation instrument in the lower half of the PFD.
Automatic Dependent Surveillance – Broadcast Out (ADS-B Out) is a function of an aircraft’s onboard electronic equipment (avionics) that periodically broadcasts the aircraft’s three-dimensional position and velocity along with additional identifying information prescribed by 14 CFR §91.227. If the aircraft is equipped with ADS-B Out, it must be in transmit mode at all times.

Figure 3-10. A typical primary flight display (PFD)
The pitot-static system provides the source of air pressure for the operation of the altimeter, airspeed indicator, and vertical speed indicator. See Figure 3-11. Pitot-static system failures will present indications as shown in Figure 3-12.

Figure 3-11. Pitot-static system

Figure 3-12. Pitot-static system failures
During attitude instrument training, the pilot must develop three fundamental skills involved in all instrument flight maneuvers:
When executing an ILS approach, the pilot must keep the aircraft on an electronic glide slope. This requires the ability to establish the proper rate of descent for the ground speed. As ground speed increases, the rate of descent required to maintain the glide slope must be increased; as ground speed decreases, the rate of descent required to maintain the glide slope also decreases. By first cross-checking the instruments and then interpreting them, the pilot is able to precisely control the aircraft to a successful landing.
The attitude of an aircraft is controlled by movement around its lateral (pitch), longitudinal (roll), and vertical (yaw) axes. In instrument flying, attitude requirements are determined by correctly interpreting the flight instruments. Instruments are grouped as to how they relate to control, function, and aircraft performance. Attitude control is discussed in terms of pitch, bank, and power control. The three pitot-static instruments, the three gyroscopic instruments, and the tachometer or manifold pressure gauge are grouped into the following categories:
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Pitch Instruments:
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Bank Instruments:
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Power Instruments:
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When climbing and descending, it is necessary to begin level-off in enough time to avoid overshooting the desired altitude. The amount of lead to level-off from a climb varies with the rate of climb and pilot technique. If the aircraft is climbing at 1,000 feet per minute, it will continue to climb at a descending rate throughout the transition to level flight. An effective practice is to lead the altitude by 10 percent of the vertical speed (500 fpm would have a 50 foot lead; 1,000 fpm would have a 100 foot lead).
The amount of lead to level-off from a descent also depends upon the rate of descent and control technique. To level-off from a descent at descent airspeed, lead the desired altitude by approximately 10 percent. For level-off at an airspeed higher than descending airspeed, lead the level-off by approximately 25 percent.
When making initial pitch attitude corrections to maintain altitude during straight-and-level flight, the changes of attitude should be small and smoothly applied. As a rule-of-thumb for airplanes, use a half-bar-width correction for errors of less than 100 feet and a full-bar-width correction for errors in excess of 100 feet.
When recovering from an unusual attitude without the aid of the attitude indicator, approximate level pitch attitude is reached when the airspeed indicator and altimeter stop moving and the vertical speed indicator reverses its trend.
The following procedures are accomplished to recover from a nose-low attitude:
The following procedures are accomplished to recover from a nose-high attitude:
[10-2024]