Navigation AidsRadio Telephony — DGCA CPL practice questions

Question 1 of 20

The ADF resolves the 180° ambiguity of the loop antenna by:

A.Using a higher frequency

B.Adding a sense antenna to form a cardioid with a single null

C.Rotating the aircraft

D.Comparing 90 and 150 Hz tones

All 20 questions — Navigation Aids

Radio Telephony · DGCA CPL. The correct option is marked on each.

Q1. The ADF resolves the 180° ambiguity of the loop antenna by:
- A.Using a higher frequency
- B.Adding a sense antenna to form a cardioid with a single null✓
- C.Rotating the aircraft
- D.Comparing 90 and 150 Hz tones
Why: dding a sense antenna to form a cardioid with a single null. The omnidirectional sense antenna combines with the figure-of-eight loop to give a cardioid with one null.
Q2. Heading 350°(M), ADF relative bearing 040°. The QDM is:
- A.310°
- B.030°✓
- C.050°
- D.210°
Why: QDM = RB + HDG = 040 + 350 = 390 − 360 = 030°.
Q3. A VOR's reference and variable 30 Hz signals are in phase when the aircraft is:
- A.Overhead the station
- B.Due magnetic north of the station✓
- C.On the 180° radial
- D.At the cone of confusion
Why: ue magnetic north of the station. By design the phase difference is zero on the 360° (north) radial; it then equals the radial.
Q4. In a conventional VOR, the reference phase signal is carried as:
- A.30 Hz AM
- B.30 Hz FM on a 9960 Hz sub-carrier✓
- C.A 90 Hz tone
- D.A Morse code
Why: CVOR: reference = FM on 9960 Hz sub-carrier (same in all directions); variable = AM from the rotating pattern.
Q5. The ILS localizer indicates centreline when:
- A.90 Hz dominates
- B.150 Hz dominates
- C.The depth of modulation of 90 and 150 Hz is equal (DDM = 0)✓
- D.The DME reads zero
Why: On the centreline the two tones are received equally — zero difference in depth of modulation.
Q6. ILS marker beacons all transmit on:
- A.329–335 MHz
- B.108.10–111.95 MHz
- C.75 MHz✓
- D.1030 MHz
Why: Outer/middle/inner markers share a 75 MHz carrier, differing in tone and code.
Q7. A false glide slope is typically encountered:
- A.Below the true 3° path
- B.Above the true path (e.g. ~6°), if intercepted from above✓
- C.On the localizer back course
- D.Only at night
Why: bove the true path (e.g. ~6°), if intercepted from above. Antenna side-lobes create false slopes at higher angles; intercept the GP from below to avoid them.
Q8. DME measures distance by:
- A.Comparing two 30 Hz phases
- B.Timing the round trip of pulse pairs, less a 50 µs ground delay✓
- C.Measuring received signal strength
- D.Counting satellites
Why: The interrogator times the reply (minus the fixed 50 µs transponder delay) to derive slant range.
Q9. At 12,000 ft (2 NM) directly overhead a DME, the indicator reads approximately:
- A.0 NM
- B.2 NM✓
- C.6 NM
- D.12 NM
Why: Overhead, ground range is zero so slant range equals height: 12,000 ft ≈ 2 NM.
Q10. An SSR transponder is interrogated on, and replies on, respectively:
- A.1090 / 1030 MHz
- B.1030 / 1090 MHz✓
- C.329 / 335 MHz
- D.75 / 75 MHz
Why: Ground interrogates on 1030 MHz; aircraft replies on 1090 MHz.
Q11. Side-Lobe Suppression in SSR prevents:
- A.Garbling
- B.FRUIT
- C.Replies to the antenna's side lobes giving false bearings✓
- D.Altitude errors
Why: A P2 control pulse stops the transponder replying when interrogated via a side lobe.
Q12. The transponder code for radio communications failure is:
- A.7500
- B.7600✓
- C.7700
- D.7000
Why: 7500 hijack, 7600 radio failure, 7700 emergency.
Q13. Which radar requires equipment carried aboard the aircraft to function?
- A.Primary radar
- B.Secondary radar✓
- C.Both
- D.Neither
Why: SSR needs a transponder; primary radar works on the passive echo from any target.
Q14. A 3-D GNSS position fix requires a minimum of how many satellites?
- A.2
- B.3
- C.4✓
- D.6
Why: Three for position plus one to solve the receiver clock error = four.
Q15. The GPS L1 carrier frequency is:
- A.1227.60 MHz
- B.1575.42 MHz✓
- C.1090 MHz
- D.1176.45 MHz
Why: L1 = 1575.42 MHz (L2 = 1227.6, L5 = 1176.45).
Q16. GAGAN is best described as:
- A.A ground-based primary radar
- B.A satellite-based augmentation system (SBAS) for the Indian region✓
- C.India's own satellite constellation for global coverage
- D.An inertial system
Why: satellite-based augmentation system (SBAS) for the Indian region. GAGAN broadcasts corrections + integrity over India via GEO satellites. (NavIC/IRNSS is the regional constellation.)
Q17. The essential difference between RNAV and RNP is that RNP adds:
- A.A higher cruising altitude
- B.On-board performance monitoring and alerting✓
- C.A second VOR
- D.Mode S
Why: RNP = RNAV plus the requirement that the system monitors its own accuracy and alerts the crew.
Q18. A TCAS Resolution Advisory commands a manoeuvre in:
- A.The horizontal plane (turn)
- B.The vertical plane (climb/descend)✓
- C.Any plane
- D.Speed only
Why: RAs are vertical-only; never turn in response to an RA.
Q19. The radio altimeter operates around 4200–4400 MHz and indicates:
- A.Pressure altitude
- B.True height above the surface directly below (AGL)✓
- C.Altitude above mean sea level
- D.Slant range to a beacon
Why: FM-CW radio altimeter gives AGL, typically 0–2500 ft.
Q20. A characteristic of INS used alone is that its position error:
- A.Is constant regardless of time
- B.Grows with time (drift), typically a few NM per hour✓
- C.Depends on satellite geometry
- D.Only occurs over the sea
Why: Integration accumulates error, so unaided INS drifts (~2 NM/hr); GNSS is used to bound it.