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TECH GENERAL — CH.17

Induction Icing and Ignition SystemsAircraft & Engines — DGCA CPL practice questions

Question 1 of 6

Carburettor icing can occur at outside air temperatures as high as:

A.0°C
B.+10°C
C.+22°C
D.+35°C

All 6 questions — Induction Icing and Ignition Systems

Aircraft & Engines · DGCA CPL. The correct option is marked on each.

  1. Q1. Carburettor icing can occur at outside air temperatures as high as:

    • A.0°C
    • B.+10°C
    • C.+22°C✓
    • D.+35°C

    Why: Fuel vaporisation plus the venturi pressure drop can cool moist air far below freezing even on a warm day — up to about +22°C OAT.

  2. Q2. With a fixed-pitch propeller, carburettor icing is indicated by:

    • A.A gradual drop in RPM✓
    • B.A gradual drop in manifold pressure
    • C.Rising CHT
    • D.Falling oil pressure

    Why: Fixed-pitch: gradual RPM drop. Constant-speed propeller: gradual manifold pressure drop.

  3. Q3. When carburettor heat is first applied with ice present, the engine will:

    • A.Immediately run smoothly
    • B.Show a further drop in power before recovering as the ice melts✓
    • C.Overspeed
    • D.Backfire continuously

    Why: Hot air is less dense so power drops first; recovery to normal (or above) confirms ice was present.

  4. Q4. With the ignition switch OFF, the magneto primary circuit is:

    • A.Open
    • B.Grounded✓
    • C.Connected to the battery
    • D.Reversed

    Why: OFF grounds the primary winding, preventing a spark. A broken ground wire gives a 'hot mag' — live even when switched off.

  5. Q5. Each cylinder has two spark plugs fed by independent magnetos in order to:

    • A.Double the engine RPM
    • B.Provide redundancy and more complete, even combustion✓
    • C.Allow the battery to be removed
    • D.Reduce plug fouling only

    Why: Dual ignition is for safety (one magneto can fail) and performance (two flame fronts burn the charge more completely).

  6. Q6. An impulse coupling:

    • A.Boosts magneto output at high RPM
    • B.Momentarily spins the magneto fast and retards timing for starting✓
    • C.Connects the two magnetos
    • D.Drives the fuel pump

    Why: At cranking speed the magneto spark is weak; the spring-loaded impulse coupling flicks it over fast and retards the spark for starting.