Flight InstrumentsAir Navigation — DGCA CPL practice questions
Question 1 of 10
The altimeter measures altitude by sensing:
All 10 questions — Flight Instruments
Air Navigation · DGCA CPL. The correct option is marked on each.
Q1. The altimeter measures altitude by sensing:
- A.Total air pressure
- B.Static atmospheric pressure✓
- C.Dynamic pressure (pitot minus static)
- D.Air temperature and density
Why: The altimeter is an aneroid barometer that measures static atmospheric pressure. As altitude increases, static pressure decreases — the instrument converts this pressure to an altitude readout.
Q2. Setting 1013.25 hPa on the altimeter sub-scale gives:
- A.Altitude above aerodrome level (AAL)
- B.Height above MSL (QNH)
- C.Pressure altitude✓
- D.True altitude
Why: With 1013.25 hPa (standard pressure) set, the altimeter reads pressure altitude — used above the transition altitude for vertical separation in the flight levels.
Q3. The Airspeed Indicator (ASI) measures:
- A.Static pressure
- B.Dynamic pressure (pitot minus static)✓
- C.Total pressure only
- D.Wind velocity relative to ground
Why: The ASI measures dynamic (impact) pressure = Pitot total pressure − static pressure. It converts this to an airspeed readout. It indicates IAS; TAS requires density correction.
Q4. The Vertical Speed Indicator (VSI) operates by:
- A.Measuring pitot pressure change rate
- B.Comparing static pressure through a calibrated leak to a reference capsule✓
- C.Gyroscopic precession sensing vertical velocity
- D.GPS altitude rate of change
Why: The VSI (or variometer) measures the rate of change of static pressure. Static pressure feeds into a capsule directly and through a calibrated metered leak to a case — the pressure difference indicates climb/descent rate.
Q5. A blocked pitot tube (but open static) will cause the ASI to:
- A.Read zero
- B.Stick at last speed in level flight; indicate climb if climbing, descent if descending✓
- C.Over-read in a climb
- D.Under-read in a descent
Why: With a blocked pitot, the trapped pressure acts like an altimeter. If altitude stays the same, IAS appears fixed. In a climb, static pressure falls → ASI over-reads (shows increase). In descent, under-reads.
Q6. The Attitude Indicator (Artificial Horizon) uses:
- A.A pendulum to detect gravity
- B.A gyroscope with its spin axis vertical (Earth gyro)✓
- C.Accelerometers only
- D.GPS attitude data
Why: The AI uses a gyroscope spinning with its axis vertical (tied to gravity through pendulous vanes or erection mechanism), maintaining a stable horizon reference regardless of aircraft manoeuvre.
Q7. The Directional Gyro (Heading Indicator) requires periodic realignment because:
- A.It is affected by compass deviation
- B.Gyroscopic rigidity causes apparent drift due to Earth's rotation and real precession✓
- C.It aligns to magnetic north automatically
- D.Temperature causes calibration error
Why: The HI/DG is subject to apparent drift (Earth's rotation makes the gyro appear to drift) and real precession (friction). It must be realigned to the magnetic compass every 10–15 minutes.
Q8. A turn coordinator (TC) indicates:
- A.Rate of turn and bank angle only
- B.Rate of turn and slip/skid via ball✓
- C.Attitude in pitch and roll
- D.Heading and rate of heading change
Why: The turn coordinator uses a gyro to sense rate of roll and yaw, displaying the rate of turn. The ball (inclinometer) indicates slip (too much rudder away from turn) or skid (too little rudder).
Q9. A standard rate turn is:
- A.1°/sec (360° in 6 min)
- B.3°/sec (360° in 2 min)✓
- C.6°/sec (360° in 1 min)
- D.2°/sec (360° in 3 min)
Why: Standard rate (Rate 1) turn = 3°/second = 180° in 1 minute = 360° in 2 minutes. Used in IFR holds and procedure turns. Bank angle for Std Rate ≈ TAS/10 + 7°.
Q10. The static vent is blocked in flight. Which instruments are most directly affected?
- A.Attitude indicator and heading indicator
- B.Altimeter, VSI, and ASI✓
- C.Turn coordinator only
- D.Magnetic compass only
Why: A blocked static vent deprives the altimeter, VSI, and ASI of updated static pressure reference — all three will freeze at the values when the blockage occurred (altimeter and VSI freeze; ASI may over/under read).