The Direct Indicating CompassNavigation — Instrumentation — DGCA CPL practice questions
Question 1 of 9
In a standby direct reading compass there is:
All 9 questions — The Direct Indicating Compass
Navigation — Instrumentation · DGCA CPL. The correct option is marked on each.
Q1. In a standby direct reading compass there is:
- A.a non-pendulously mounted magnet system
- B.a single pendulously mounted bar magnet
- C.a circular magnet or pair of bar magnets pendulously mounted✓
- D.a low magnetic moment system, either of circular or bar configuration
Why: The vertical card compass (standby DRC) uses either a circular magnet or two, four, or six short bar magnets to increase pole strength while minimising moment of inertia. All configurations are pendulously mounted to achieve horizontality. See Section 3 . — The design uses multiple short magnets rather than one long one — this keeps mass near the centre, reduces moment of inertia, and improves damping. More magnets = higher pole strength without longer length.
Q2. The main requirements of a direct reading magnetic compass are that it should be:
- A.horizontal, sensitive, periodic
- B.easily read, floating in a transparent liquid, quick to react to change in aircraft heading
- C.positioned directly in front of the pilot, easily corrected for magnetic deviation, aperiodic
- D.aperiodic, horizontal, sensitive✓
Why: The three key requirements are Horizontal, Sensitive, and Aperiodic — these must all be met for the compass to work reliably in all phases of flight. See Section 3 . — The three requirements — Horizontal, Sensitive, Aperiodic — are always examined together. Learn them in any order.
Q3. For a position in the southern hemisphere, the effect of acceleration errors are greatest on headings:
- A.180° and 360°
- B.045° and 225°
- C.135° and 315°
- D.090° and 270°✓
Why: Acceleration errors are maximum on East and West headings (090° and 270°) in both hemispheres. The rule does not change between hemispheres — only the direction of the apparent turn changes (towards the nearer pole, which is south in the SH). See Section 8 . — Maximum acceleration error = E/W in BOTH hemispheres. This applies regardless of which hemisphere you're in — only the direction of the apparent turn changes.
Q4. An aircraft in the southern hemisphere is turning from a heading of 090°C to 360°C using a DGI. At the end of the turn the compass will read ....... than 360° and liquid swirl will ....... this effect.
- A.more; increase
- B.less; increase
- C.more; decrease
- D.less; decrease✓
Why: The aircraft is turning left (from 090 to 360°) through north in the Southern Hemisphere. North is the FURTHER pole in the SH (south is nearer). Turning through the further pole, the magnet assembly is thrown out in the OPPOSITE direction to the turn (clockwise here, while the aircraft turns anticlockwise), so at the end of the turn the compass reads LESS than 360°. Liquid swirl acts in the direction of the aircraft's turn, which opposes that displacement, so the swirl REDUCES the error. Answer: less; decrease
Q5. In a standby compass the magnet system is immersed in a transparent liquid. The purpose of this liquid is to:
- A.increase sensitivity, increase aperiodicity✓
- B.increase sensitivity, decrease aperiodicity
- C.increase sensitivity at high latitudes, lubricate bearings
- D.increase sensitivity, reduce liquid swirl
Why: The liquid serves two main functions: (1) it lubricates the pivot and provides buoyancy, reducing effective weight → lower friction → increased sensitivity; (2) it acts as a damping medium → increased aperiodicity (faster settling). See Section 4 . — Liquid = sensitivity (buoyancy/lubrication) + aperiodicity (damping). Liquid swirl is a downside of the liquid, not a benefit. Low viscosity helps minimise swirl.
Q6. To improve the horizontality of a compass, the magnet assembly is suspended from a point:
- A.on the centre line of the magnet
- B.below the centre of gravity
- C.above the centre of gravity✓
- D.varying with magnetic latitude
Why: Pendulous suspension requires the pivot to be above the CG. With the CG below the pivot, the weight of the assembly acts to oppose the dip-induced tilt caused by Z, keeping the magnets near horizontal. See Section 3.1 . — Pivot ABOVE CG = pendulous = stable = horizontal. This is the same principle as a pendulum. The weight of the assembly always acts to restore horizontal when pivoted from above the CG.
Q7. The magnitude, and sense, of turning error shown by a direct reading compass varies with: [6 statements listed] — Of these statements:
- A.only 1, 2, 5 and 6 are correct
- B.only 1, 3, 5 and 6 are correct
- C.only 2, 4 and 5 are correct
- D.all are correct✓
Why: All six factors affect turning error: (1) design of compass, (2) direction of turn, (3) rate of turn, (4) hemisphere, (5) heading, (6) dip at the aircraft's latitude. Each of these directly influences the magnitude and/or sense (clockwise/anticlockwise) of the magnet assembly displacement during a turn. See Section 9 and Section 11 . — Turning error factors: DRAT-HLC → Design, Rate of turn, Heading, Dip (latitude), direction of turn (Hemisphere), Compass design, Latitude. When the answer is "all", eliminate distractors by confirming each factor is genuine.
Q8. During a sustained turn ....... the nearer magnetic pole, the effect of liquid swirl will ....... compass turning error.
- A.away from; increase
- B.towards; not affect
- C.away from; not affect
- D.towards; increase✓
Why: When turning towards the nearer pole (through north in NH, through south in SH), the magnet assembly and liquid both rotate in the same direction as the aircraft. Liquid swirl reinforces the magnet's rotation, increasing the turning error. See Section 10 . — Towards nearer pole → sluggish → swirl increases. Away from nearer pole (= towards further) → lively → swirl decreases. Simple rule: swirl always acts in the direction of turn = same direction as the nearer-pole error = adds to nearer-pole error.
Q9. When carrying out a turn at the magnetic equator there will be:
- A.no turning error
- B.a tendency to under-read turns through south and over-read turns through north
- C.a tendency to under-read turns due to liquid swirl✓
- D.no turning error when turning through east or west
Why: At the magnetic equator Z = 0 → no dip-based turning error. However, liquid swirl still exists as a small residual error. Swirl turns the magnet in the direction of the aircraft's turn — for a right turn this is clockwise → compass under-reads. So there IS a small turning error due to liquid swirl alone. See Section 10 . — At equator: Z=0, no dip, no main turning error — but liquid swirl still exists. Swirl acts in direction of turn = clockwise turn = compass under-reads slightly. This is a subtle but testable distinction.