The Airspeed Indicator (ASI)Navigation — Instrumentation — DGCA CPL practice questions
Question 1 of 9
A leak in the pitot total pressure line of a non-pressurized aircraft to an airspeed indicator would cause it to:
All 9 questions — The Airspeed Indicator (ASI)
Navigation — Instrumentation · DGCA CPL. The correct option is marked on each.
Q1. A leak in the pitot total pressure line of a non-pressurized aircraft to an airspeed indicator would cause it to:
- A.Over-read in a climb and under-read in a descent
- B.Over-read
- C.Under-read in a climb and over-read in a descent
- D.Under-read✓
Why: A leak in the pitot line causes loss of dynamic pressure reaching the capsule. With lower pressure on the inside of the capsule, the differential (pitot − static) is reduced. The capsule expands less → ASI under-reads regardless of flight phase. See Section 8 . — Distinction: Pitot BLOCKAGE → no change in level flight, under-reads in descent. Pitot LEAK → always under-reads.
Q2. A pitot blockage of both the ram air input and the drain hole with the static port open causes the airspeed indicator to:
- A.Read a little low
- B.Read a little high
- C.React like an altimeter✓
- D.Freeze at zero
Why: If both the ram air input AND the drain hole are blocked, pitot pressure is completely trapped (no air in or out of the pitot side). The capsule has fixed pitot pressure on one side and variable static pressure on the other. As altitude changes, only the static pressure changes — exactly as in an altimeter. The ASI needle rises in a climb and falls in a descent. See Section 7 . — The key is that both the input AND the drain hole are blocked. If only the ram air input is blocked but the drain hole is open, pressure in the pitot side gradually equalises to static, and the ASI would tend towar…
Q3. If the static line to the ASI becomes blocked during a long descent, a dangerous situation could arise due to the ASI:
- A.Over-reading, this indicated speed falsely showing the aircraft to be further from the stalling speed than it actually is✓
- B.Under-reading, this indicated speed falsely showing the aircraft to be closer to the stalling speed than it actually is
- C.Under-reading, this indicated speed possibly leading to the operation of flaps and/or landing gear at speeds in excess of safety speeds
- D.Over-reading, this indicated speed possibly leading to the operation of flaps and/or landing gear at speeds in excess of safety speeds
Why: With a blocked static during a descent, the frozen static pressure (from a higher altitude) is lower than the actual external static pressure. The differential (pitot − frozen lower static) is larger than reality → ASI over-reads. The pilot sees a higher speed than actual → believes they are safely above stall when they may not be. This is the "Static Over-reads in Descent" part of PUDSOD. See Section 7 . — PUDSOD: Pitot Under-reads in Descent; Static Over-reads in Descent. Over-reading ASI on approach is the most dangerous scenario — the pilot may fly too slowly.
Q4. An aircraft maintaining a constant CAS and altitude is flying from a cold airmass into warmer air. The effect of the change of temperature on the speed will be:
- A.CAS will decrease
- B.EAS will increase
- C.TAS will increase✓
- D.TAS will decrease
Why: At constant altitude and CAS, the dynamic pressure is constant. Moving into warmer air at the same pressure altitude reduces air density (warm air is less dense). Since TAS = EAS × (density correction), and density has decreased, a higher TAS is needed to maintain the same dynamic pressure and therefore the same CAS. See Section 4 . — Rule: Constant CAS + higher temperature (lower density) = higher TAS. Warm air = less dense = faster true speed for same dynamic pressure.
Q5. The airspeed indicator is calibrated to:
- A.Conditions of the International Standard Atmosphere at all heights
- B.Conditions of the International Standard Atmosphere at MSL✓
- C.An air density of 1013.25 g/m³
- D.Indicate correctly in any atmosphere
Why: The ASI is calibrated to read true airspeed only at ISA MSL conditions: density 1225 g/m³ , pressure 1013.25 hPa , temperature +15°C . No allowance is made for density change with altitude. See Section 3 . — Common trap: confusing 1013.25 (the pressure in hPa) with the calibration density (1225 g/m³). These are completely different values.
Q6. Dynamic pressure is equal to:
- A.½ ρV²✓
- B.½ Vρ²
- C.(½ ρV)²
- D.½ (ρV)²
Why: Dynamic pressure Q = ½ρV², where ρ is air density and V is True Airspeed. This is the fundamental formula from fluid mechanics. Only V is squared, not ρ. See Section 1 . — Only V is squared. The factor ½ and the squaring of V are both essential parts of the formula. Many candidates incorrectly square ρ or the entire expression.
Q7. Excluding blockages, the full list of errors of the ASI is:
- A.Instrument error, position error, density error, manoeuvre induced error
- B.Instrument error, position error, temperature error, compressibility error, manoeuvre induced error
- C.Instrument error, position error, barometric error, temperature error, lag, manoeuvre induced error
- D.Instrument error, position error, density error, compressibility error, manoeuvre induced error✓
Why: The five ASI errors are: instrument error (manufacturing), position/pressure error (static sensing), density error (altitude effect on density), compressibility error (air compressibility at speed), and manoeuvre-induced error (pitch changes). See Section 4 . — 5 ASI errors: I-P-D-C-M — Instrument, Position, Density, Compressibility, Manoeuvre-induced.
Q8. Some ASIs have coloured arcs and lines marked on their dials. A yellow arc and a white arc indicate:
- A.Cautionary range and normal operating range
- B.Flap operating speed range and normal operating range
- C.Cautionary range and flap operating speed range✓
- D.Flap operating speed range and cautionary range
Why: Yellow arc = caution range (V NO to V NE ); White arc = flap operating range (V S0 to V FE ). Green arc is the normal operating range. See Section 6 . — Arc colour memory aid: White = Wings (flaps are wing devices); Green = Go (safe normal ops); Yellow = Yield (caution); Red = Stop (never exceed).
Q9. If the static line to the ASI becomes blocked during a climb, the ASI reading will:
- A.Increase, no matter what the actual airspeed is
- B.Progressively under indicate the value of airspeed✓
- C.Progressively over indicate the value of airspeed
- D.Stick at the airspeed showing at the moment of blockage
Why: During a climb, outside static pressure decreases with altitude. With a blocked static line, the frozen static pressure (from the lower altitude at blockage) is higher than the actual external pressure. The differential (pitot − frozen higher static) is less than actual dynamic pressure → ASI under-reads. The further the climb continues, the greater the error becomes (progressively). See Section 7 . — PUDSOD covers descent effects. For climb: Pitot blocked → over-reads; Static blocked → under-reads. Both effects worsen progressively as the aircraft moves further from the blockage altitude.