Characteristics and General DefinitionsNavigation — Instrumentation — DGCA CPL practice questions

All 8 questions — Characteristics and General Definitions

Navigation — Instrumentation · DGCA CPL. The correct option is marked on each.

1. Q1. Which of the following lists correctly identifies all four fundamental characteristics common to all aviation instrumentation systems?

   • A.Range, resolution, accuracy, reliability✓
   • B.Range, sensitivity, linearity, durability
   • C.Resolution, calibration, linearity, repeatability
   • D.Accuracy, precision, sensitivity, reliability

   Why: Range, resolution, accuracy and reliability are the four general characteristics of every instrumentation system, from a simple dial to a glass-cockpit display. Memorise the four together.

2. Q2. Standard atmospheric pressure is:

   • A.1013.25 hPa = 29.92 mmHg = 14.7 psi
   • B.1013.25 mb = 29.92 inHg = 760 mmHg = 14.7 psi
   • C.1013.25 hPa = 29.92 inHg = 760 mmHg = 14.7 psi✓
   • D.1025 hPa = 29.92 inHg = 760 mmHg = 14.7 psi

   Why: Standard atmosphere = 1013.25 hPa = 1013.25 mb = 29.92 inHg = 760 mmHg = 14.7 psi . Note: hPa and mb are numerically identical. See Section 1 . — The most tested equivalence: 1013.25 hPa = 29.92 inHg. These two are critical for altimeter setting questions throughout the course.

3. Q3. A Vertical Speed Indicator (VSI) uses a non-linear (logarithmic) scale. The reason for this is:

   • A.To allow the instrument to cover a wider total range of vertical speeds
   • B.To show low rates of climb/descent more accurately than high rates✓
   • C.To compensate for the non-linear change in atmospheric pressure with altitude
   • D.To allow a single pointer to make multiple revolutions without confusion

   Why: On a logarithmic (non-linear) scale, the graduations are finer at the low end and coarser at the high end. This is deliberate — accurate reading of small rates of climb/descent is operationally more important (e.g. during cruise altitude capture) than reading a high rate precisely. See Section 3 . — Key phrase: "low rates are more easily read than high rates" — this exactly matches the source text.

4. Q4. On a three-pointer altimeter, the three pointers are geared such that:

   • A.Long pointer = 10 000 ft/rev; middle = 1 000 ft/rev; small = 100 ft/rev
   • B.Long pointer = 1 000 ft/rev; middle = 10 000 ft/rev; small = 100 000 ft/rev✓
   • C.Long pointer = 100 ft/rev; middle = 1 000 ft/rev; small = 10 000 ft/rev
   • D.Long pointer = 1 000 ft/rev; middle = 100 ft/rev; small = 10 000 ft/rev

   Why: The source text states: long pointer covers 1 000 ft per revolution (each division = 100 ft); middle pointer covers 10 000 ft per revolution (each division = 1 000 ft); smallest pointer covers 100 000 ft (each division = 10 000 ft). See Section 3 . — The longest pointer is the most sensitive : 1 rev = 1 000 ft. The shortest pointer covers the most range: 1 rev = 100 000 ft. Think: long = precise = 1 000 ft.

5. Q5. Why is an analogue pointer retained on otherwise digital altimeter displays?

   • A.Because regulations require both analogue and digital displays on transport aircraft
   • B.Because pilots are more familiar with analogue instruments from training
   • C.Because the human eye cannot easily interpret rate of change from moving numbers✓
   • D.Because digital counters are insufficiently accurate for altitude display

   Why: The source text explicitly states that the human eye and brain cannot easily interpret rate information from moving numbers. Pilots derive important secondary information about vertical rate from the angular rate of the altimeter pointer — something digital counters cannot convey effectively. See Section 5 . — This is a human factors principle: rate perception requires a moving pointer, not changing digits. It applies to altimeters, airspeed indicators, and any instrument where trend information matters.

6. Q6. What is parallax error in an instrument?

   • A.The error caused by the instrument being out of calibration
   • B.The error caused by viewing the instrument from an angle other than directly from the front✓
   • C.The lag between a parameter changing and the instrument showing the new value
   • D.The error caused by temperature changes in the instrument mechanism

   Why: Parallax occurs when the eye, the pointer index, and the scale are not aligned — specifically when viewing the instrument from the side instead of head-on. The misalignment of the line of sight causes the pointer to appear to point to a different graduation than it actually does. See Section 6 . — The remedy for parallax error is designing instruments with the pointer as close to the scale as possible, or using a mirror strip on the scale to allow the pilot to align their eye correctly.

7. Q7. On a conventional (non-electronic) instrument, a yellow or amber arc indicates:

   • A.Normal operating range
   • B.Cautionary range✓
   • C.Warning or unsafe operating range
   • D.Flap operating range

   Why: Standard colour coding for conventional instruments: Green = normal; Yellow/Amber = cautionary; Red = warning/unsafe. See Section 7 . — Three colours for conventional instruments: G-Y-R (Green/Yellow/Red = Go/Caution/Stop). CS-25 electronic displays add White (present status) and Blue (temporary situation).

8. Q8. In the CS-25 colour standardisation for electronic (glass cockpit) displays, the colour BLUE indicates:

   • A.Normal operating range
   • B.Warning or unsafe condition
   • C.Present status information
   • D.Temporary situation✓

   Why: CS-25 defines: White = present status; Blue = temporary situation; Green = normal operating range; Yellow/Amber = cautionary; Red = warning/unsafe. See Section 7 . — The two CS-25 additions to the basic colour code that students most commonly confuse are White (present status) and Blue (temporary situation). Remember: White = What's happening NOW; Blue = Brief/temporary.