Instrument Written Test – Airplane Instruments

When taxiing, the magnetic compass should be checked to make sure that the compass card is swinging freely and indicating known headings.

If you roll into a smooth, coordinated, standard-rate turn to the left or right from an east or west heading, the compass will indicate the approximate correct magnetic heading. There are no turning errors on turns from east or west headings.

If you roll into a smooth, coordinated, standard-rate turn to the left or right from an east or west heading, the compass will normally indicate the approximate correct magnetic heading. Acceleration, not turning, errors are found in east or west headings in the Northern Hemisphere.

In turns from a southerly heading in the Northern Hemisphere, the compass leads the turn. That is, it indicates a turn in the proper direction but at a faster rate than is actually occurring.

In a turn through north or south, the compass indication will usually be incorrect. But in a turn through east or west, the compass indication is usually accurate. Therefore, the compass should be indicating properly when passing through 90° and 270° This holds true for only medium to shallow bank turns, e.g., 15-30°

Magnetic dip causes a compass needle to point both down toward the earth and to the magnetic pole. This characteristic causes turning errors.

In turns from a southerly heading in the Northern Hemisphere, the compass leads the turn. That is, it indicates a turn in the proper direction but at a rate faster than the actual rate.

If you roll into a smooth, coordinated, standard-rate turn to the left or right from an east or west heading, the compass will indicate the approximate correct magnetic heading. There are no turning errors on turns from east or west headings.

In turns from a northerly heading in the Northern Hemisphere, the compass will initially indicate a turn to the opposite direction. Then the compass heading will lag behind the actual heading until the airplane approaches an east or west heading.

If you roll into a smooth, coordinated, standard-rate turn to the left or right from an east or west heading, the compass will indicate the approximate correct magnetic heading. Turning errors appear on turns from north or south headings, not east or west.

In turns from a northerly heading in the Northern Hemisphere, the compass will initially indicate a turn to the opposite direction, and the compass heading will lag behind actual until the airplane approaches an east or west heading.

The pitot-static system is a source of pressure for the altimeter, vertical speed indicator, and airspeed indicator. The pitot tube is connected directly to the airspeed indicator, and the static vents are connected directly to all three. The pressure of air coming into the pitot tube (impact air pressure) is compared with the air pressure at the static system vents to determine airspeed.

When the airspeed indicator pitot tube and drain hole are blocked, the airspeed indicator will react as an altimeter. There will be a constant pressure within the pitot tube, and as the pressure from the static source decreases during a climb, the indicated airspeed on the altimeter will increase.

When the airspeed indicator pitot tube and drain hole are blocked, the airspeed indicator will react as an altimeter. There will be a constant pressure within the pitot tube, and as the pressure from the static source decreases during a climb, the indicated airspeed on the altimeter will increase.

If both the pitot tube input and the drain hole on the pitot system are blocked, the airspeed indication will be constant at any given altitude.

As temperature increases, pressure levels rise farther above sea level and true altitude increases given a constant indicated altitude. As altitude increases with constant power, true airspeed increases.

Most aircraft equipped with a pitot-static system are provided with an alternate source of static pressure for emergency use. This source is usually vented inside the cabin. The pressure within an unpressurized cockpit is slightly lower than the pressure outside the airplane because of the Venturi effect of the air moving past the outside of the cockpit. When the alternate static source is used, the altimeter and airspeed indicator will read higher than actual, and the vertical speed indicator will momentarily show a climb.

Most aircraft equipped with a pitot-static system are provided with an alternate source of static pressure for emergency use. This source is usually vented inside the cabin. The pressure within an unpressurized cockpit is slightly lower than the pressure outside the airplane because of the Venturi effect of the air moving past the outside of the cockpit. When the alternate static source is used, the altimeter will read higher than actual, and the vertical speed indicator will momentarily show a climb.

Most aircraft equipped with a pitot-static system are provided with an alternate source of static pressure for emergency use. This source is usually vented inside the cabin. The pressure within an unpressurized cockpit is slightly lower than the pressure outside the airplane because of the Venturi effect of the air moving past the outside of the cockpit. When the alternate static source is used, the altimeter and airspeed indicator will read higher than actual, and the vertical speed indicator will momentarily show a climb.

The vertical speed indicator operates from the static pressure source and indicates change in pressure. Thus, if the static pressure ports became iced over, there would be no change in the static pressure, and there would be no indication of descent or climb.

The needle of the vertical speed indicator (VSI) should indicate zero when the aircraft is on the ground or is maintaining a constant pressure level in flight. If it does not indicate zero, you must allow for the error when interpreting the indications in flight. Since the VSI is not a required instrument, you may fly when it is out of adjustment.

The Mach meter indicates the ratio of aircraft true airspeed to the speed of sound at flight altitude. It uses the pressure differential between the impact and static air sources and corrects automatically for temperature and altitude.

Set the altimeter to the local altimeter setting before taking off, and verify that the indication is within 75 ft. of the actual elevation. If the difference is greater than 75 ft., you should consult an instrument repair shop.

Set the altimeter to the local altimeter setting before taking off, and verify that the indication is within 75 ft. of the actual elevation. If the difference is greater than 75 ft., you should consult an instrument repair shop.

Pressure altitude is the altitude read on your altimeter when the instrument is adjusted to indicate height above the standard datum plane, i.e., an altimeter setting of 29.92 in. The standard datum plane is a theoretical level where the weight of the atmosphere is 29.92 in. of Hg.

Because the altimeter in each airplane is equally affected by temperature and pressure variation errors, use of the local altimeter setting in a given area provides for better vertical separation of aircraft.

When indicating 8,000 ft., an altimeter has the short hand (1,000-ft. intervals) on 8, the long hand (100-ft. intervals) on zero, and the thin hand with flared tip (10,000-ft. intervals) just below 1, as shown in altimeter 2.

When indicating 12,000 ft., an altimeter has the long hand (100-ft. intervals) on 0, the short hand (1,000-ft. intervals) on 2, and the thin hand with flared tip (10,000-ft. intervals) just over 1, as shown in altimeter 4.

The altimeter setting is the value which permits the altimeter to indicate the true altitude at field elevation. Within the vicinity of a particular airport, the altimeter setting provides an accurate means of separating traffic vertically and also provides obstruction clearance. Note that the use of the word "true" here is not completely accurate because the altimeter setting does not correct for nonstandard temperature.

The altimeter setting is the value which permits the altimeter to indicate the true altitude at field elevation. Within the vicinity of a particular airport, the altimeter setting provides an accurate means of separating traffic vertically and also provides obstruction clearance. Note that the use of the word "true" here is not completely accurate because the altimeter setting does not correct for nonstandard temperature.

If you cannot obtain an altimeter setting at an airport, adjust your altimeter so it reads the current airport elevation.

Pressure altitude is indicated when the altimeter is set to 29.92.

Pressure altitude by definition is indicated altitude when the altimeter setting is 29.92. This is true regardless of area or true altitude.

The pressure altitude is determined by setting your altimeter to 29.92 and reading the altitude indicated. No matter what altitude or location, the altimeter reads pressure altitude when the barometric window is set to 29.92" Hg.

Pressure altitude can be determined anywhere by setting the altimeter to 29.92.

Rotating the altimeter's setting knob to a higher (or lower) barometric setting moves the hands to higher (or lower) indicated altitude at the rate of 1" Hg to 1,000 ft. of altitude. Given the current altimeter setting of 30.42 and the indicated altitude of 6,500 ft., resetting the window to 29.92 would lower indicated altitude by 500 ft. (30.42 - 29.92 = 0.5" Hg = 500 ft.). The new indicated altitude would be 6,000 ft. MSL, which would be pressure altitude.

During IFR flight in Class E airspace below 18,000 ft. MSL, ATC periodically provides altimeter settings. Thus, you will continually hear the altimeter settings given to other pilots as you monitor ATC.

Above 18,000 ft. MSL (FL 180), pressure altitude is used to separate traffic. Pressure altitude is the altitude indicated on an altimeter when it is set to 29.92.

When you are at an altitude of 18,000 ft. MSL (FL 180) or higher, the altimeter should be set to 29.92, which is pressure altitude. It does not matter whether you are on an airway.

The pressure altitude is 25,000 ft. in your area because at FL 250 your altimeter should be set at 29.92. A flight level (FL) by definition means a pressure altitude.

One in. of pressure equals approximately 1,000 ft. of altitude. If an altimeter should be set to 30.57 but is set to 29.92, it is set .65" Hg too low and thus will indicate 650 ft. (1,000 ft. x .65) less than actual altitude. Thus, if the airplane lands at an airport with a field elevation of 650 ft., the altimeter will indicate sea level, i.e., 650 ft. elevation minus the 650 ft. altimeter setting error.

One in. of pressure equals approximately 1,000 ft. of altitude. If an altimeter should be set to 30.26 but is set to 29.92, it is set .34 in. Hg too low and thus will indicate 340 ft. (1,000 ft. x .34) less than actual altitude. Thus, if the airplane lands at an airport with a field elevation of 134 ft., the altimeter will indicate 206 ft. below sea level (134 ft. airport elevation - 340 ft. altimeter setting error).

Pressure altitude will equal true altitude when standard atmospheric conditions exist at the current altitude, i.e, 29.92" Hg and 15°C at sea level.

Density altitude, by definition, is pressure altitude adjusted for nonstandard temperature. Accordingly, pressure altitude will equal density altitude at standard temperature.

When temperature lowers en route, you are lower than your altimeter indicates. Similarly, when you are in colder-than-standard air temperatures, true altitude is lower than pressure altitude.

Altimeter settings vary approximately 1" Hg for each 1,000 ft. of altitude. When the altimeter setting is changed from 30.11 to 29.96, it is lower by .15" Hg. Thus, the altimeter will indicate 150 ft. lower (1,000 ft. x .15). Remember that the indicated altitude and altimeter setting vary directly; i.e., when the altimeter setting is adjusted up, indicated altitude increases and vice versa.

When temperatures are warmer than standard, the pressure levels are raised. That is, the altimeter will indicate an altitude lower than that at which the aircraft is actually flying.

Electric gyro instruments can be checked for irregular noises by listening to them after the battery is turned on but before the engine is started. You should notice any bearing clatters, clicks, or other unusual noises. Additionally, you can look at the instruments to see if they are in their expected positions. There are additional tests to pursue after the engine is started.

Newton's second law of motion states that the deflection of a moving body is proportional to the deflective force applied and is inversely proportional to its weight and speed. For a gyro, the resistance to deflection is proportional to the deflective force. This property is used by the attitude indicator.

Vacuum-driven gyros take several minutes to get up to speed. After about 5 min., set the heading indicator to the correct magnetic heading. After taxiing to the runup area, verify that the heading indicator still indicates the correct magnetic heading.

Some remote indicating compasses (RIC) have a separate slaving control and compensator unit with a deviation meter. The instrument shows any difference between the displayed heading and the magnetic heading. It also provides the controls shown in Fig. 143 to correct any errors. To correct from 120° indicated on the RIC to the magnetic heading of 110° select the free gyro mode and depress the clockwise heading drive button until 110° heading on RIC is indicated and the deviation meter is centered.

A left compass card error means that the card has rotated too far to the left; i.e., it reads too high a heading. The clockwise adjustment rotates the indicating compass card to the right to eliminate left compass card error. For example, this would change a 120° heading to 110°

If the heading on the compass is left of that desired, the compass has rotated too far to the right, which is a right compass error. Thus, the slaving control must be placed in the free mode, and the counterclockwise drive button must be depressed.

The pretakeoff check for attitude indicators is that, within the 5-min. warm-up, the horizon bar should erect to the horizontal position and remain at the correct position. It should remain stable during straight taxiing and taxi turns.

The horizon bar in an attitude indicator should not tilt more than 5° during a taxi turn. If it does, it is unreliable and should not be used for IFR flight.

The attitude indicator normally erects itself by discharging air equally through four exhaust ports, each of which is partially covered by a pendulous vane. During coordinated (and skidding) turns, centrifugal force moves the vanes from their vertical position, precessing the gyro toward the inside of the turn.
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In 180° coordinated steep turns, when the airplane is rolled out to straight-and-level flight, the attitude indicator will indicate a turn to the opposite direction along with a slight climb.

In 180° coordinated steep turns, when the airplane is rolled out to straight-and-level flight, the attitude indicator will indicate a turn to the opposite direction along with a slight climb. Thus, the indicated turn would be to the left if the steep turn were made to the right.

Similarly to coordinated turns, the attitude indicator will show a bank in the opposite direction when the aircraft is rolled out of a skidding turn. However, there will be no nose-up indication.

Errors for both pitch and bank indication on an attitude indicator are greatest when rolling out of a 180° turn. This precession error, normally between 3° and 5° is self-correcting by the part of the heading indicator called the erecting mechanism.

Deceleration affects some attitude indicators through precession to incorrectly indicate a descent.

Acceleration affects some attitude indicators through precession to incorrectly indicate a climb.

Prior to starting an engine, you should determine that the needle of the turn-and-slip indicator is approximately centered and that the tube is full of fluid with the ball also approximately centered if the airplane is on a level surface.

During taxi, the turn-and-slip indicator ball should move freely opposite the direction of any turn since centrifugal force forces the ball to the outside. Also, the rate of turn indicator should indicate a turn in the proper direction.

The turn coordinator indicates rate of roll and rate of turn. When the bank is constant, the rate of turn is indicated. When the bank is changing, the rate of roll is also indicated.

The turn coordinator indicates rate of roll and rate of turn. When the bank is constant, the rate of turn is indicated. When the bank is changing, the rate of roll is also indicated.

The miniature aircraft of the turn coordinator indicates the rate of roll when bank is changing. When the rotation around the longitudinal axis is zero, the instrument indicates the rate of turn. Thus, it provides only an indirect indication of the angle of bank.

The displacement of a turn coordinator increases as angle of bank (in coordinated flight) increases because the turn coordinator shows rate of turn, which increases as angle of bank increases.

On a taxiing turn to the left, the turn coordinator shows a turn to the left, and the ball moves to the right. The centrifugal force of the turn, which is not offset by bank when taxiing, forces the ball opposite to the turn.