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Brunei DCA CPL(A) Instrumentation study materials
Brunei DCA CPL(A) Instrumentation study resources

Brunei DCA CPL(A) Instrumentation practice questions

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Question 1Fundamentals of flight instruments: pressure sensing, gyroscopic principles, and instrument errors

In a light aircraft, the static pressure source becomes partially blocked during a climb. What indication will the airspeed indicator show compared with the true airspeed?

  1. An airspeed lower than the true value Correct answer.
  2. A steady airspeed that does not change
  3. An airspeed equal to the true value
  4. An airspeed higher than the true value

Explanation

The airspeed indicator compares pitot (total) pressure with static pressure. If the static source is blocked while the aircraft climbs, the trapped static pressure remains at the higher value from the lower altitude, so the pressure difference across the capsule is smaller than it should be and the indicated airspeed under-reads.

Question 2Fundamentals of flight instruments: pressure sensing, gyroscopic principles, and instrument errors

Which instrument uses the difference between total pressure and static pressure as its operating principle?

  1. The airspeed indicator Correct answer.
  2. The turn coordinator
  3. The vertical speed indicator
  4. The altimeter

Explanation

The airspeed indicator is the only pitot-static instrument that senses total (pitot) pressure directly. Its capsule expands according to the difference between pitot pressure and static pressure, and this difference is calibrated to display airspeed.

Question 3Fundamentals of flight instruments: pressure sensing, gyroscopic principles, and instrument errors

What is the purpose of the calibrated leak in a vertical speed indicator?

  1. To provide a reference pressure so that a rate of change is displayed Correct answer.
  2. To damp out vibration from the engine
  3. To correct the reading for temperature
  4. To allow the capsule to expand with altitude

Explanation

The VSI capsule is connected to the static source through a calibrated orifice, so the pressure inside the capsule lags behind the changing static pressure in the case. The resulting differential drives the needle, and this differential exists only while altitude is changing, giving a rate indication.

Question 4Fundamentals of flight instruments: pressure sensing, gyroscopic principles, and instrument errors

An aircraft on the ground at an elevation of 1,200 ft has its altimeter subscale set to 1013 hPa while the local QNH is 1003 hPa. What will the altimeter approximately indicate?

  1. 2,000 ft
  2. 1,500 ft Correct answer.
  3. 900 ft
  4. 1,200 ft

Explanation

The subscale is set higher than the actual QNH by 10 hPa. A 1 hPa error corresponds to roughly 30 ft, so the altimeter over-reads by about 300 ft, giving approximately 1,500 ft. Setting the subscale above the true QNH always causes the altimeter to indicate higher than the true elevation.

Question 5Fundamentals of flight instruments: pressure sensing, gyroscopic principles, and instrument errors

What is meant by the term 'rigidity in space' as applied to a gyroscope?

  1. The ability of the rotor to increase its speed when torque is applied
  2. The tendency of the spin axis to remain fixed in direction in inertial space Correct answer.
  3. The tendency of the gyro to precess when the aircraft turns
  4. The property that makes the gyro align with the local vertical

Explanation

Rigidity in space describes the property whereby a spinning rotor resists any change in the orientation of its spin axis. Because the axis stays fixed relative to inertial space, it can be used as a stable reference for attitude or heading.

Question 6Fundamentals of flight instruments: pressure sensing, gyroscopic principles, and instrument errors

A force is applied to the spin axis of a spinning gyroscope. The axis then moves in a direction at right angles to the applied force. What is this behaviour called?

  1. Erection
  2. Drift
  3. Rigidity
  4. Precession Correct answer.

Explanation

Precession is the response of a spinning gyroscope to an applied torque: the spin axis moves at right angles to the direction of the applied force. It is the property used in rate instruments and in the erection systems of gyroscopic instruments.

Question 7Fundamentals of flight instruments: pressure sensing, gyroscopic principles, and instrument errors

Which instrument depends on the gyroscopic property of rigidity in space for its indication?

  1. The rate of climb indicator
  2. The airspeed indicator
  3. The turn coordinator
  4. The heading indicator Correct answer.

Explanation

The heading indicator uses a gyroscope whose spin axis remains fixed in space, so the aircraft's heading changes are shown as relative movement between the case and the stable gyro. This is a direct application of rigidity in space.

Question 8Fundamentals of flight instruments: pressure sensing, gyroscopic principles, and instrument errors

What is the source of the suction or vacuum used to drive a typical light aircraft's gyroscopic instruments?

  1. An engine-driven vacuum pump Correct answer.
  2. The pitot pressure line
  3. The aircraft's electrical generator
  4. A ram-air venturi only

Explanation

Most light aircraft use an engine-driven vacuum pump to draw air through the gyro cases, spinning the rotors. Some older installations use a venturi, but the engine-driven pump is the standard source in modern light aircraft.

Question 9Fundamentals of flight instruments: pressure sensing, gyroscopic principles, and instrument errors

What causes apparent wander of a gyroscope's spin axis when the aircraft flies at high latitude?

  1. Earth's rotation combined with the gyro's rigidity in space Correct answer.
  2. Magnetic variation at the aircraft's position
  3. Changes in the vacuum pump output
  4. Friction in the rotor bearings only

Explanation

A gyro whose axis is fixed in inertial space appears to drift relative to the Earth because the Earth rotates beneath it. This apparent wander is greatest near the poles and is zero at the equator for a horizontal spin axis.

Question 10Fundamentals of flight instruments: pressure sensing, gyroscopic principles, and instrument errors

An aircraft flies at 180 kt on a northerly heading. The heading indicator's apparent wander due to Earth's rotation is greatest at which latitude?

  1. The equator
  2. The geographic pole Correct answer.
  3. The magnetic pole
  4. About 45 degrees north

Explanation

Apparent wander of a gyro with a horizontal spin axis is proportional to the sine of the latitude. It is zero at the equator and reaches its maximum at the geographic pole, where the full rate of Earth's rotation appears as drift.

Question 11Fundamentals of flight instruments: pressure sensing, gyroscopic principles, and instrument errors

What is the purpose of the erection system in an artificial horizon?

  1. To correct the indication for airspeed
  2. To spin the rotor up to operating speed
  3. To indicate the rate of turn to the pilot
  4. To keep the gyro axis aligned with the true vertical Correct answer.

Explanation

The erection system uses pendulous vanes or similar devices to sense any tilt of the gyro away from the vertical and to apply small torques that correct it. This keeps the horizon bar aligned with the true horizon during manoeuvres.

Question 12Fundamentals of flight instruments: pressure sensing, gyroscopic principles, and instrument errors

During a prolonged coordinated turn, the erection system of a vacuum-driven artificial horizon may produce what error?

  1. A false descent indication Correct answer.
  2. A false climb indication
  3. A false turn indication
  4. A false pitch-up indication

Explanation

In a sustained coordinated turn, centrifugal force acts on the pendulous vanes so that they sense a false vertical. The erection system then tilts the gyro, causing the instrument to indicate a descent or turn error after the manoeuvre.

Question 13Fundamentals of flight instruments: pressure sensing, gyroscopic principles, and instrument errors

What does the turn coordinator indicate?

  1. Rate of climb and descent
  2. Rate of turn and whether the turn is coordinated Correct answer.
  3. Angle of bank only
  4. Heading relative to magnetic north

Explanation

The turn coordinator displays rate of turn and, through the inclinometer ball, whether the turn is coordinated. It is a rate gyro that responds to yaw and, in some designs, roll.

Question 14Fundamentals of flight instruments: pressure sensing, gyroscopic principles, and instrument errors

Why is a turn coordinator preferred to a turn and slip indicator for showing the quality of a turn in some aircraft?

  1. It is unaffected by turbulence
  2. It displays the magnetic heading directly
  3. It indicates rate of roll as well as rate of yaw Correct answer.
  4. It requires no electrical power

Explanation

The turn coordinator's gyro is canted so that it responds to roll as well as yaw, allowing it to indicate the rate of turn during the roll-in and roll-out of a turn. A turn and slip indicator responds mainly to yaw rate.

Question 15Fundamentals of flight instruments: pressure sensing, gyroscopic principles, and instrument errors

What is the purpose of the inclinometer (the ball) in a turn coordinator?

  1. To indicate the angle of attack
  2. To measure the rate of turn
  3. To show whether the turn is coordinated Correct answer.
  4. To display the slipstream direction

Explanation

The inclinometer shows the resultant of gravity and centrifugal force, so the ball moves to the inside of an uncoordinated turn. Centring the ball with rudder produces a coordinated turn.

Question 16Fundamentals of flight instruments: pressure sensing, gyroscopic principles, and instrument errors

Which error of the magnetic compass occurs when the aircraft accelerates or decelerates on an easterly or westerly heading?

  1. Deviation
  2. Acceleration error Correct answer.
  3. Turning error
  4. Variation

Explanation

Acceleration error occurs on east or west headings because the compass pivot and the centre of gravity of the magnet system are not coincident. The compass indicates a turn toward north when accelerating and toward south when decelerating on those headings.

Question 17Fundamentals of flight instruments: pressure sensing, gyroscopic principles, and instrument errors

The magnetic compass is most reliable for straight flight on which headings?

  1. Any heading in level flight
  2. North and south Correct answer.
  3. East and west
  4. Northeast and southwest

Explanation

On north and south headings the compass is least affected by acceleration error, because the magnet system is aligned with the magnetic meridian and the dip effect is minimal. Turning error, however, is greatest on these headings during turns.

Question 18Fundamentals of flight instruments: pressure sensing, gyroscopic principles, and instrument errors

What is compass deviation?

  1. The error caused by the aircraft's own magnetic fields Correct answer.
  2. The angular difference between true north and magnetic north
  3. The error caused by the Earth's magnetic field
  4. The error caused by acceleration of the aircraft

Explanation

Deviation is the angular difference between the magnetic heading and the compass heading, caused by magnetic fields generated by the aircraft's structure and electrical equipment. It is determined by a compass swing and recorded on a deviation card.

Question 19Fundamentals of flight instruments: pressure sensing, gyroscopic principles, and instrument errors

A pilot wishes to fly a magnetic heading of 090 degrees. The deviation card shows a deviation of +4 degrees on that heading. What compass heading should be flown?

  1. 090 degrees
  2. 098 degrees
  3. 094 degrees
  4. 086 degrees Correct answer.

Explanation

Deviation is applied in the opposite sense to obtain compass heading from magnetic heading. With a deviation of +4 degrees, the compass heading is 090 minus 4, which is 086 degrees.

Question 20Fundamentals of flight instruments: pressure sensing, gyroscopic principles, and instrument errors

What is indicated airspeed (IAS)?

  1. The true speed of the aircraft relative to the air
  2. The airspeed corrected for temperature and density
  3. The airspeed read directly from the instrument without correction Correct answer.
  4. The airspeed corrected for position and instrument error

Explanation

Indicated airspeed is the value shown on the airspeed indicator dial, uncorrected for any error. Applying position and instrument corrections gives calibrated airspeed, which is the next step in the correction chain.

Question 21Fundamentals of flight instruments: pressure sensing, gyroscopic principles, and instrument errors

What is the relationship between true airspeed and indicated airspeed at a constant indicated airspeed as altitude increases?

  1. True airspeed decreases as altitude increases
  2. True airspeed remains constant with altitude
  3. True airspeed is always less than indicated airspeed
  4. True airspeed increases as altitude increases Correct answer.

Explanation

As altitude increases, air density falls, so a given dynamic pressure corresponds to a higher true airspeed. For a constant indicated airspeed, the true airspeed rises by roughly 2 per cent per 1,000 ft at lower altitudes.

Question 22Fundamentals of flight instruments: pressure sensing, gyroscopic principles, and instrument errors

What causes position error in a pitot-static system?

  1. Errors due to the compressibility of air at high speed
  2. Errors due to the temperature of the instrument
  3. Errors due to the lag of the instrument mechanism
  4. Errors due to the location of the static ports and the airflow around the aircraft Correct answer.

Explanation

Position error arises because the static pressure at the actual static port location differs from the true ambient static pressure, owing to airflow and angle of attack effects. It is determined during flight testing and corrected to give calibrated airspeed.

Question 23Fundamentals of flight instruments: pressure sensing, gyroscopic principles, and instrument errors

What is the purpose of the alternate static source in a light aircraft?

  1. To provide a static pressure source if the normal static ports become blocked Correct answer.
  2. To supply vacuum to the gyroscopic instruments
  3. To provide pitot pressure if the pitot tube becomes blocked
  4. To measure the outside air temperature

Explanation

The alternate static source allows the pilot to select a different static pressure source, usually inside the cabin, if the normal static ports become blocked. The resulting indications will differ slightly from normal because the cabin pressure differs from ambient.

Question 24Fundamentals of flight instruments: pressure sensing, gyroscopic principles, and instrument errors

If the pitot tube becomes completely blocked while the aircraft is in level flight, what will the airspeed indicator do?

  1. It will indicate zero
  2. It will continue to indicate the airspeed at the time of blockage Correct answer.
  3. It will indicate an increasing airspeed in a climb
  4. It will indicate the true airspeed accurately

Explanation

With the pitot tube blocked, the pressure trapped in the capsule is fixed. In level flight at constant altitude the static pressure also stays constant, so the pressure difference does not change and the indicator remains at the value at the moment of blockage.

Question 25Fundamentals of flight instruments: pressure sensing, gyroscopic principles, and instrument errors

Why is the static pressure source used by the altimeter, airspeed indicator and vertical speed indicator shared in a typical installation?

  1. To reduce weight and complexity while providing a common reference Correct answer.
  2. To allow the airspeed indicator to use pitot pressure directly
  3. To ensure the gyros receive vacuum pressure
  4. To eliminate the need for a pitot tube

Explanation

A single static source supplies all three pressure instruments, reducing weight and plumbing complexity and ensuring they share a common reference pressure. If that source becomes blocked, all three instruments are affected simultaneously.

Question 26Fundamentals of flight instruments: pressure sensing, gyroscopic principles, and instrument errors

A light aircraft climbs at a constant indicated airspeed while the pilot maintains a steady rate of climb. What happens to the pressure inside the case of the vertical speed indicator during the climb?

  1. It stays exactly equal to static pressure at all times, so the needle remains at zero
  2. It oscillates rapidly around static pressure, producing a vibration of the needle
  3. It rises above static pressure, which drives the needle downwards into a descent indication
  4. It falls slowly towards the static pressure, so the instrument shows a steady climb rate Correct answer.

Explanation

The vertical speed indicator compares the pressure inside its case with the pressure inside a calibrated capsule connected to the static source. A restrictor or calibrated leak lets case pressure lag behind the changing static pressure, so in a climb the case pressure remains momentarily higher than the capsule pressure and the linkage shows a climb. Once the rate of climb becomes constant the lag closes and the needle settles at the corresponding rate.

Question 27Fundamentals of flight instruments: pressure sensing, gyroscopic principles, and instrument errors

Which property of a gyroscope explains why the rotor of a heading indicator tends to maintain its orientation in space?

  1. Precession
  2. Gimballing freedom
  3. Rigidity in space Correct answer.
  4. Centrifugal relief

Explanation

Rigidity in space, also called gyroscopic inertia, is the tendency of a spinning rotor to keep its spin axis fixed in inertial space provided no external torque acts on it. This property is what allows the heading indicator and artificial horizon to provide a stable reference. Precession is a separate property describing the response of the spin axis to an applied torque.

Question 28Fundamentals of flight instruments: pressure sensing, gyroscopic principles, and instrument errors

An aircraft flies at 45 degrees north latitude at a groundspeed of 240 kt on a heading of 360 degrees (north). Using the approximation that apparent wander due to Earth's rotation equals 15 degrees per hour multiplied by the sine of the latitude, what is the approximate apparent wander rate of an uncompensated directional gyro?

  1. About 11 degrees per hour, drifting to the right Correct answer.
  2. About 21 degrees per hour, drifting to the left
  3. About 15 degrees per hour, drifting to the left
  4. About 4 degrees per hour, drifting to the right

Explanation

The horizontal component of Earth's rotation seen by the gyro is proportional to the sine of the latitude, so at 45 degrees the rate is 15 x sin 45, which is about 10.6 degrees per hour. Because the aircraft is heading north in the northern hemisphere, the apparent wander appears as a drift of the indicated heading to the right, requiring periodic correction by the pilot. Transport wander is a separate effect and is not included in this figure.

Question 29Fundamentals of flight instruments: pressure sensing, gyroscopic principles, and instrument errors

An aircraft with a suction-driven artificial horizon is accelerating in level flight. What indication error does the erection mechanism produce, and why?

  1. A false descent indication, because the rotor speed falls during acceleration
  2. A false climb indication, because the pendulous vanes sense the apparent vertical created by the acceleration Correct answer.
  3. A false turn indication, because the gyro precesses about the vertical axis
  4. No error, because the erection system responds only to gravity

Explanation

The erection system uses pendulous vanes or a similar gravity-sensing device that aligns the gyro with the apparent vertical. During acceleration the apparent vertical tilts rearwards relative to the true vertical, so the mechanism erects the horizon towards a nose-up attitude. The result is a false climb indication while the aircraft is accelerating, with the opposite error during deceleration.

Question 30Fundamentals of flight instruments: pressure sensing, gyroscopic principles, and instrument errors

A pilot suspects that the static port is partially blocked. Which combination of indications is most consistent with this condition?

  1. All three pressure instruments read steadily higher than actual values at all altitudes
  2. Airspeed under-reads in the climb and over-reads in the descent, while the altimeter and vertical speed indicator lag
  3. The airspeed indicator reads zero while the altimeter and vertical speed indicator remain accurate
  4. Airspeed over-reads in the climb and under-reads in the descent, while the altimeter and vertical speed indicator lag Correct answer.

Explanation

If the static port is blocked, trapped static pressure stays at the value present when the blockage occurred. In a climb the true static pressure falls below the trapped value, so the airspeed indicator senses an excessive pressure difference and over-reads; in a descent the true pressure rises above the trapped value and the instrument under-reads. The altimeter and vertical speed indicator also respond only to the trapped pressure and therefore lag or freeze.

Question 31Pitot-static system: airspeed indicator, altimeter, vertical speed indicator - construction, operation, and errors

Which two pressures are compared by the airspeed indicator to produce an indicated airspeed?

  1. Total pressure and cabin pressure
  2. Impact pressure and pitot pressure
  3. Dynamic pressure and static pressure Correct answer.
  4. Static pressure and total pressure

Explanation

The airspeed indicator responds to the difference between pitot (total) pressure and static pressure. This difference is dynamic pressure, and the instrument is calibrated so that dynamic pressure is displayed as a speed. Total pressure alone cannot give speed because the static component must be subtracted.

Question 32Pitot-static system: airspeed indicator, altimeter, vertical speed indicator - construction, operation, and errors

An aircraft climbs at a constant true airspeed while the static source remains normal. What happens to the indicated airspeed?

  1. It remains constant at the same TAS
  2. It increases as altitude rises
  3. It fluctuates with the vertical speed
  4. It decreases as altitude rises Correct answer.

Explanation

Indicated airspeed depends on dynamic pressure, which falls as air density decreases with altitude for a given true airspeed. Therefore, holding TAS constant in a climb causes the ASI reading to decrease. The relationship is the basis of the TAS greater than IAS rule at altitude.

Question 33Pitot-static system: airspeed indicator, altimeter, vertical speed indicator - construction, operation, and errors

The altimeter is essentially a barometer that measures which quantity?

  1. Total pressure minus static pressure
  2. Dynamic pressure from the pitot tube
  3. Absolute static pressure from the static source Correct answer.
  4. The rate of change of static pressure

Explanation

The altimeter is a pressure instrument that senses static pressure and displays it as an altitude using a standard pressure-height relationship. It does not use pitot pressure at all. The subscale setting allows the pilot to reference the display to a chosen pressure datum.

Question 34Pitot-static system: airspeed indicator, altimeter, vertical speed indicator - construction, operation, and errors

What does the vertical speed indicator display?

  1. The difference between pitot and static pressure
  2. The rate of change of static pressure Correct answer.
  3. The rate of change of true airspeed
  4. The absolute altitude above the pressure datum

Explanation

The VSI is connected only to the static source and responds to the rate at which static pressure changes. A climb produces decreasing static pressure, which the instrument converts into a positive rate of climb. It gives no information about speed or absolute altitude.

Question 35Pitot-static system: airspeed indicator, altimeter, vertical speed indicator - construction, operation, and errors

The pressure inside the VSI case is deliberately made to lag behind the pressure inside the capsule by means of a calibrated leak. What is the purpose of this design?

  1. To damp out turbulence-induced needle vibration
  2. To produce a usable deflection that indicates the rate of change Correct answer.
  3. To compensate for temperature changes in the capsule
  4. To allow the instrument to indicate altitude as well

Explanation

Because the case pressure lags the capsule pressure through the calibrated leak, a pressure difference exists whenever static pressure is changing. That difference deflects the capsule and drives the needle, so the deflection is proportional to the rate of change. When the pressure stabilises, the leak equalises the pressures and the needle returns to zero.

Question 36Pitot-static system: airspeed indicator, altimeter, vertical speed indicator - construction, operation, and errors

With the VSI in level flight at constant altitude, the needle shows zero. What does this indicate about static pressure?

  1. Static pressure is decreasing steadily
  2. Static pressure is equal to pitot pressure
  3. Static pressure is below the standard datum
  4. Static pressure is constant Correct answer.

Explanation

The VSI indicates the rate of change of static pressure, so a zero reading means the static pressure is not changing. Constant static pressure corresponds to level flight at a steady altitude. It says nothing about the actual value of static pressure or about pitot pressure.

Question 37Pitot-static system: airspeed indicator, altimeter, vertical speed indicator - construction, operation, and errors

What is the purpose of the barometric subscale (pressure setting) on an altimeter?

  1. To set the datum pressure to which the indicated altitude is referenced Correct answer.
  2. To compensate the capsule for temperature at high altitude
  3. To correct the instrument for airspeed-related position error
  4. To zero the needle after maintenance adjustments

Explanation

The subscale allows the pilot to set the reference pressure in the altimeter's aneroid mechanism. Changing the setting shifts the whole altitude scale so that indicated altitude is measured from the chosen pressure datum, such as QNH, QFE or standard pressure. This is essential for terrain clearance and for flight levels.

Question 38Pitot-static system: airspeed indicator, altimeter, vertical speed indicator - construction, operation, and errors

An aircraft flies from an area of high pressure to an area of low pressure without the altimeter subscale being changed. If the aircraft maintains a constant indicated altitude, what happens to its true altitude?

  1. It changes only if temperature also changes
  2. It increases above the indicated value
  3. It stays equal to the indicated value
  4. It decreases below the indicated value Correct answer.

Explanation

The altimeter interprets static pressure as altitude using the datum set on the subscale. When the aircraft enters lower-pressure air, the pressure at a given true altitude is lower, so the altimeter over-reads altitude and the aircraft is actually lower than indicated. The rule is high to low, look out below.

Question 39Pitot-static system: airspeed indicator, altimeter, vertical speed indicator - construction, operation, and errors

What is the effect of extremely cold temperature on the true altitude of an aircraft flying at a constant indicated altitude?

  1. True altitude equals indicated altitude
  2. True altitude is higher than indicated altitude
  3. True altitude is unaffected by temperature
  4. True altitude is lower than indicated altitude Correct answer.

Explanation

In cold air the pressure levels are compressed toward the surface, so a given static pressure occurs at a lower true altitude than the altimeter assumes. The altimeter therefore over-reads and the aircraft is lower than indicated. This is why cold-temperature altitude corrections are applied on approach.

Question 40Pitot-static system: airspeed indicator, altimeter, vertical speed indicator - construction, operation, and errors

The static ports become completely blocked during a climb, while the pitot tube remains clear. What does the airspeed indicator do?

  1. It reads a constant value regardless of speed changes
  2. It drops immediately to zero
  3. It behaves like an altimeter, increasing as the aircraft climbs Correct answer.
  4. It continues to indicate correctly

Explanation

With the static port blocked, the pressure trapped in the static line stays at the value present at the moment of blockage. The ASI then responds only to changes in pitot pressure, so it acts like an altimeter: climbing raises pitot pressure relative to the trapped static and the reading increases. Descending produces the opposite effect.

Question 41Pitot-static system: airspeed indicator, altimeter, vertical speed indicator - construction, operation, and errors

During a descent the pitot tube becomes blocked while the drain hole remains clear. What happens to the indicated airspeed?

  1. It freezes at the value at the moment of blockage
  2. It remains correct because the static source is open
  3. It decreases toward zero as the aircraft descends Correct answer.
  4. It increases steadily as the aircraft descends

Explanation

A blocked pitot tube with a clear drain hole allows the trapped pitot pressure to vent to static pressure. As the aircraft descends, static pressure rises and the trapped pitot pressure follows it, so the pressure difference falls and the ASI indicates a decreasing speed. The indication eventually reaches zero even though the aircraft is flying.

Question 42Pitot-static system: airspeed indicator, altimeter, vertical speed indicator - construction, operation, and errors

Which statement best describes the effect of position error on the pitot-static system?

  1. It is the difference between indicated and calibrated airspeed due to instrument friction
  2. It results from the altimeter subscale being set to the wrong pressure
  3. It arises from incorrect pressure sensed at the static ports because of airflow around the aircraft Correct answer.
  4. It is caused by leakage in the static line

Explanation

Position error, also called pressure error, occurs because the static ports do not sense true ambient static pressure at all attitudes and speeds. Local airflow and angle of attack alter the pressure at the port, so the ASI, altimeter and VSI all receive a slightly erroneous static pressure. The error varies with configuration and speed and is usually tabulated by the manufacturer.

Question 43Pitot-static system: airspeed indicator, altimeter, vertical speed indicator - construction, operation, and errors

What is meant by the term instrument error in the context of pitot-static instruments?

  1. The error caused by the static ports sensing disturbed airflow
  2. The error introduced by a leaking pitot line
  3. The error caused by flying in air that is not standard
  4. The error inherent in the manufacture and adjustment of the instrument Correct answer.

Explanation

Instrument error is the residual error resulting from manufacturing tolerances, friction and calibration imperfections within the instrument itself. It is normally small and is checked during periodic instrument inspections. It should be distinguished from position error, density error and installation errors.

Question 44Pitot-static system: airspeed indicator, altimeter, vertical speed indicator - construction, operation, and errors

Which of the following describes the effect of a leaking static line on the pitot-static instruments?

  1. The instruments indicate higher than actual speed and altitude
  2. The VSI shows a steady climb in level flight
  3. The ASI under-reads and the altimeter over-reads at altitude Correct answer.
  4. The ASI over-reads while the altimeter under-reads

Explanation

A leak in the static line lets cabin or higher-pressure air enter the system, so the static pressure sensed is higher than true ambient static pressure at altitude. The greater pressure difference drives the ASI to over-read, while the altimeter interprets the higher pressure as a lower altitude and therefore under-reads. This is a potentially dangerous combination.

Question 45Pitot-static system: airspeed indicator, altimeter, vertical speed indicator - construction, operation, and errors

Which colour marking on the airspeed indicator identifies the speed that must not be exceeded in any operation?

  1. The lower end of the green arc
  2. The middle of the green arc
  3. The upper end of the yellow arc, marked by a red line Correct answer.
  4. The start of the white arc

Explanation

The red radial line at the top of the yellow arc marks VNE, the never-exceed speed. The yellow arc itself represents the caution range, which may be used only in smooth air. The white arc marks the flap operating range and the green arc the normal operating range.

Question 46Pitot-static system: airspeed indicator, altimeter, vertical speed indicator - construction, operation, and errors

The white arc on an airspeed indicator represents which speed range?

  1. The normal operating range
  2. The caution range for smooth air only
  3. The flap operating range Correct answer.
  4. The never-exceed range

Explanation

The white arc extends from the stalling speed with flaps extended to the maximum speed at which flaps may be extended. It defines the permitted flap operating range. The green arc defines the normal range and the yellow arc the caution range.

Question 47Pitot-static system: airspeed indicator, altimeter, vertical speed indicator - construction, operation, and errors

An aircraft is on the ground at an airfield where the altimeter reads the aerodrome elevation with QNH set. The pilot then sets QFE. What should the altimeter read?

  1. Zero, or close to zero Correct answer.
  2. The standard pressure altitude
  3. A negative value below the scale
  4. The aerodrome elevation

Explanation

QFE is the pressure at the aerodrome reference point, so setting QFE on the subscale makes the altimeter read height above that point rather than altitude above mean sea level. On the ground at the reference point this is zero. Setting QNH instead makes the instrument read aerodrome elevation.

Question 48Pitot-static system: airspeed indicator, altimeter, vertical speed indicator - construction, operation, and errors

What is pressure altitude?

  1. The altitude indicated when the subscale is set to 1013.25 hPa Correct answer.
  2. The altitude indicated with QNH set
  3. The altitude above the aerodrome reference point
  4. The true altitude corrected for temperature

Explanation

Pressure altitude is the altitude displayed when the altimeter subscale is set to the standard pressure of 1013.25 hPa. It is used for flight levels and for performance calculations. It differs from indicated altitude, which uses the local or regional pressure setting.

Question 49Pitot-static system: airspeed indicator, altimeter, vertical speed indicator - construction, operation, and errors

Why is the airspeed indicator calibrated in terms of dynamic pressure rather than true airspeed?

  1. Because the instrument responds physically to pressure difference, which varies with density Correct answer.
  2. Because dynamic pressure depends only on the aircraft's mass
  3. Because static pressure is constant at all altitudes
  4. Because true airspeed cannot be measured by any instrument

Explanation

The ASI is a pressure gauge that measures the difference between pitot and static pressure. Dynamic pressure depends on both true airspeed and air density, so the same pressure difference corresponds to different true airspeeds at different densities. The instrument is therefore calibrated to a standard density, giving indicated airspeed.

Question 50Pitot-static system: airspeed indicator, altimeter, vertical speed indicator - construction, operation, and errors

At a given true airspeed, how does indicated airspeed compare with true airspeed at high altitude?

  1. Indicated airspeed equals true airspeed
  2. Indicated airspeed is less than true airspeed Correct answer.
  3. Indicated airspeed is independent of altitude
  4. Indicated airspeed is greater than true airspeed

Explanation

At high altitude the air density is lower, so a given true airspeed produces less dynamic pressure. The ASI therefore indicates a lower speed than the actual true airspeed. The difference grows with altitude and is the reason for using a navigation computer or TAS formula.