CPL Aircraft General Knowledge 3 — Questions and Answers
Question 1: The primary cause of the lag experienced with a vertical speed indicator (VSI) is:
- Gyroscopic precession in the instrument mechanism
- The time required for pressure changes to pass through the calibrated leak (Correct answer)
- Friction in the mechanical indicator linkage
- The inertia of the diaphragm capsule assembly
Correct answer: The time required for pressure changes to pass through the calibrated leak
VSI lag of 6–9 seconds results from the time required for pressure differences to equalize through the instrument's calibrated metering orifice.
Question 2: When an altimeter is set to 29.92 in. Hg, the altitude displayed is:
- True altitude above mean sea level
- Density altitude corrected for temperature
- Pressure altitude (Correct answer)
- Field elevation above sea level
Correct answer: Pressure altitude
Setting 29.92 in. Hg (standard sea-level pressure) into the altimeter causes it to read pressure altitude, the basis for flight level operations.
Question 3: If the pitot tube becomes completely blocked (with static port open), the airspeed indicator will:
- Drop immediately to zero
- Act like an altimeter, increasing with climb and decreasing with descent (Correct answer)
- Remain fixed at the airspeed when blockage occurred
- Fluctuate in proportion to turbulence
Correct answer: Act like an altimeter, increasing with climb and decreasing with descent
A blocked pitot tube traps ram pressure; as altitude changes, only static pressure varies, making the ASI behave like an altimeter.
Question 4: The attitude indicator (artificial horizon) uses which gyroscopic principle to maintain its reference?
- Gyroscopic precession
- Rigidity in space (Correct answer)
- Coriolis effect
- Tumbling tendency
Correct answer: Rigidity in space
The attitude indicator's gyroscope relies on rigidity in space — a spinning gyro resists changes to its orientation, maintaining a fixed attitude reference.
Question 5: A heading indicator must be periodically synchronized with the magnetic compass because:
- Magnetic variation changes with aircraft heading
- Gyroscopic precession and bearing friction cause gradual drift (Correct answer)
- Airspeed changes affect gyro rotation speed
- The Earth's magnetic field induces torque on the gyro
Correct answer: Gyroscopic precession and bearing friction cause gradual drift
Gyroscopic precession and mechanical bearing friction cause the heading indicator to drift from its true heading, requiring resynchronization approximately every 15 minutes.
Question 6: The turn coordinator differs from the older turn-and-slip indicator in that it detects:
- Rate of yaw only, providing more accurate turn rate
- Rate of roll only, providing earlier turn indication
- Both rate of roll and rate of yaw (Correct answer)
- Slip and skid without indicating turn rate
Correct answer: Both rate of roll and rate of yaw
The turn coordinator's gyro is canted 30° from horizontal, making it sensitive to both roll rate and yaw rate inputs, providing an earlier turn indication.
Question 7: With the static port completely blocked, what happens to the airspeed indicator as the aircraft climbs?
- ASI reads higher than actual because frozen static is relatively high pressure (Correct answer)
- ASI reads lower than actual because pitot drops but static is frozen
- ASI is unaffected since pitot pressure dominates the reading
- ASI reads zero because no differential pressure is measurable
Correct answer: ASI reads higher than actual because frozen static is relatively high pressure
A frozen static port holds a relatively high pressure; as the aircraft climbs, ambient (and pitot) pressure drops but static stays high, so the ASI overreads.
CPL Aircraft General Knowledge 3
The primary cause of the lag experienced with a vertical speed indicator (VSI) is: