Capt Pankaj Pahil
www.ghostaviator.com
Capt Pankaj Pahil
www.ghostaviator.com
Capt Pankaj Pahil
DGCA CPL / ATPL Study Notes • Radio Navigation • Ch 19

📚 Chapter 19: Revision Questions
243-Question DGCA CPL/ATPL Bank • All Topics

Topics: VDF • ADF/NDB • VOR • ILS • Radar • DME • SSR • AWR/MLS • GNSS/RNAV/Mixed

📡 VDF (Q1–5)

Q1. VDF — which emergency frequency most commonly used for position fix?
(a) 121.500 MHz
(b) 243.000 MHz
(c) 156.8 MHz
(d) 406 MHz
Ans: (a) — VDF is triggered when aircraft transmits on 121.500 MHz. Ground DF equipment takes a bearing on the transmission.
Q2. Aircraft equipment needed for VDF let-down:
(a) VHF radio only
(b) VOR receiver
(c) VOR/DME
(d) Nothing — all ground-based
Ans: (a) — VDF needs only a VHF radio in the aircraft. All DF equipment is ground-based.
Q3. VDF station at 400 ft, aircraft at FL090. Max range?
(a) 117 NM
(b) 124 NM
(c) 134 NM
(d) 140 NM
Ans: (c) — 1.23×(√400+√9000)=1.23×(20+94.9)=1.23×114.9=141 NM. Nearest = 140 NM (d). [Answer key = c for variant with 325/8000 ft: 1.23×(18+89)=134 NM]
Q4. VDF accuracy class 'A':
(a) ±1°
(b) ±2°
(c) ±5°
(d) ±10°
Ans: (a) — VDF Class A: ±1°. Class B: ±2°. Class C: ±5°. Class D: ±10°.
Q5. VDF uses which propagation:
(a) Sky wave
(b) Ground wave
(c) Line of sight
(d) Surface wave
Ans: (c) — VDF VHF: line of sight propagation.

📡 ADF / NDB (Q6–18)

Q6. Wavelength of 375 kHz NDB signal:
(a) 8 m
(b) 80 m
(c) 800 m
(d) 8000 m
Ans: (c) — λ=300,000,000/375,000=800 m.
Q7. NDB signal pattern:
(a) 30 Hz polar diagram
(b) Omni-directional
(c) Bi-lobal
(d) Beam rotating at 30 Hz
Ans: (b) — NDB radiates omni-directionally. The ADF loop aerial is directional.
Q8. ADF accuracy within DOC by day:
(a) ±1°
(b) ±2°
(c) ±5°
(d) ±10°
Ans: (c) — ADF accuracy by day: ±5°.
Q9. Night effect on ADF worst at:
(a) Midday
(b) Midnight
(c) Dawn and dusk
(d) Noon and midnight
Ans: (c) — Night effect (sky wave interference) worst at dawn and dusk when D-layer dissolves.
Q10. Two NDBs — 20 NM from coast vs 50 NM inland. Greatest coastal refraction error?
(a) 20 NM beacon
(b) 50 NM inland beacon
(c) Equal at RB 090/270
(d) Equal at RB 000/180
Ans: (b) — Beacon further inland produces more coastal refraction — signal crosses coast at more oblique angle.
Q11. NDB range doubling — power increase needed:
(a) 4×
(b) 8×
(c) 16×
(d) 2×
Ans: (c) — Power ∝ Range⁴. Double range: power = 2⁴ = 16.
Q12. Quadrantal error in ADF caused by:
(a) Night effect
(b) Metallic airframe re-radiating signal
(c) Coastal refraction
(d) Precipitation static
Ans: (b) — Quadrantal error: metallic airframe refracts/re-radiates signal at 45° quadrants.
Q13. ADF action for bearing — which aerials?
(a) Loop only
(b) Sense only
(c) Both loop and sense
(d) Neither — automatic
Ans: (c) — ADF needs both loop (directional null) and sense (resolve 180° ambiguity).
Q14. Coastal error worst when beacon is:
(a) Inland, acute angle to coast
(b) Inland, 90° to coast
(c) Close to coast, acute angle
(d) Close to coast, 90° to coast
Ans: (a) — Worst: inland beacon, signal at acute angle to coastline.
Q15. Most significant ADF error:
(a) Quadrantal error
(b) Mountain effect
(c) Night effect
(d) Coastal refraction
Ans: (c) — Night effect (sky wave) is most significant ADF error.
Q16. ADF bearing inaccuracies caused by: (select best group)
(a) Static interference, height, SA
(b) Mountain effect, SA, night effect
(c) Lack of warning, station interference, static
(d) Coastal refraction, slant range, night effect
Ans: (c) — Valid ADF errors: lack of failure warning, station interference, static interference (also night, coastal, QE, mountain).
Q17. NDB frequency band:
(a) 250–450 kHz
(b) 190–1750 kHz
(c) 108–117.95 MHz
(d) 329–335 MHz
Ans: (b) — NDB: 190–1750 kHz (LF/MF).
Q18. BFO switch on ADF used when:
(a) Always on
(b) Required for NON emission beacons to produce audible ident
(c) Increases range
(d) Reduces quadrantal error
Ans: (b) — BFO needed for NON (unmodulated CW) beacons — heterodynes the carrier to produce audible ident tone.

📡 VOR (Q19–35)

Q19. VOR bearing measurement principle:
(a) Phase comparison
(b) Switched cardioids
(c) DDM
(d) Pulse technique
Ans: (a) — VOR: phase comparison between 30 Hz FM reference and 30 Hz AM variable.
Q20. VOR variation applied at:
(a) Aircraft for both
(b) VOR station for radial; aircraft for ADF
(c) VOR station for both
(d) Aircraft for VOR; station for ADF
Ans: (b) — VOR radials referenced to magnetic north at station. ADF uses variation at aircraft.
Q21. Aircraft flies due south of VOR. Var at station 13°W. Radial?
(a) 167°
(b) 180°
(c) 193°
(d) 347°
Ans: (c) — True bearing from station = 180° (south). Magnetic radial = 180° + 13°W = 193°.
Q22. VOR radial 250 selected, CDI 5 dots left (1 dot = 2°). OBS to centre?
(a) 240
(b) 260
(c) 250
(d) 245
Ans: (b) — 5 dots left = 10° right of track. Select 250+10 = 260°.
Q23. VOR frequency band:
(a) 190–1750 kHz
(b) 108–117.95 MHz
(c) 329–335 MHz
(d) 960–1215 MHz
Ans: (b) — VOR: 108–117.95 MHz VHF.
Q24. VOR ident tone frequency:
(a) 400 Hz
(b) 1020 Hz
(c) 1350 Hz
(d) 3000 Hz
Ans: (b) — VOR ident: 1020 Hz Morse every 10 s. DME ident: 1350 Hz.
Q25. VOR scalloping caused by:
(a) Mountains
(b) Multipath/terrain reflections
(c) Night effect
(d) Precipitation
Ans: (b) — Scalloping: multipath propagation from reflections.
Q26. DVOR advantage over CVOR:
(a) Higher power
(b) More channels
(c) Less siting error/scalloping
(d) Greater range
Ans: (c) — DVOR: electronic rotation → less siting error and scalloping.
Q27. VOT should indicate on any radial:
(a) 000° FROM
(b) 180° FROM
(c) 090° TO
(d) Varies by position
Ans: (a) — VOT: always 000° FROM (or 180° TO).
Q28. VOR reference phase transmitted as:
(a) 30 Hz AM direct
(b) 30 Hz FM on 9960 Hz sub-carrier
(c) 50 Hz modulation
(d) 400 Hz sub-carrier
Ans: (b) — Reference: 9960 Hz sub-carrier FM at 30 Hz, omni. Variable: 30 Hz AM rotating pattern.
Q29. VORTAC: civil aircraft uses:
(a) TACAN bearing only
(b) VOR bearing + TACAN DME
(c) VOR only
(d) TACAN DME only
Ans: (b) — Civil: VOR bearing + TACAN DME.
Q30. VOR site error typical maximum:
(a) ±1°
(b) ±3°
(c) ±5°
(d) ±10°
Ans: (b) — VOR site error (terrain reflections): up to ±3°.
Q31. VOR cone of confusion unreliable signals begin at approximately:
(a) Directly overhead
(b) 45° elevation
(c) 30° elevation
(d) 10° elevation
Ans: (c) — Cone of confusion starts at ≈30° elevation above VOR.
Q32. En-route VOR DOC:
(a) 25 NM
(b) 50 NM
(c) 100 NM
(d) 200 NM
Ans: (d) — En-route VOR: 200 NM.
Q33. OBS 090° TO, CDI centred, heading 080°. Aircraft:
(a) On 090° radial heading to VOR
(b) On 270° radial heading to VOR
(c) On 270° radial heading away
(d) On 090° radial heading away
Ans: (b) — 090° TO = aircraft on 270° radial. CDI centred. Heading 080° ≈ toward VOR → 270° radial, heading toward VOR.
Q34. VOR emission type:
(a) NON
(b) A9W
(c) F3N
(d) P0N
Ans: (b) — VOR: A9W.
Q35. DVOR — rotating pattern produced by:
(a) Rotating aerial mechanism
(b) Electronic switching of aerial array
(c) Doppler shift of carrier
(d) FM modulation of sub-carrier
Ans: (b) — DVOR: electronic switching of aerial array (no moving parts → less siting error).

📡 ILS (Q36–60)

Q36. ILS localizer frequency band (odd decimals only):
(a) 108–117.95 MHz
(b) 108–111.975 MHz
(c) 329–335 MHz
(d) 960–1215 MHz
Ans: (b) — LOC: 108–111.975 MHz VHF, odd-decimal tenths.
Q37. ILS glideslope frequency band:
(a) 108–111.975 MHz
(b) 329–335 MHz
(c) 960–1215 MHz
(d) 75 MHz
Ans: (b) — G/S: 329–335 MHz UHF.
Q38. ILS glideslope usable range:
(a) 5 NM
(b) 10 NM
(c) 15 NM
(d) 25 NM
Ans: (b) — G/S usable range: 10 NM.
Q39. ILS: aircraft at 3° G/S, 10 NM from threshold. Height?
(a) 2000 ft
(b) 2500 ft
(c) 3000 ft
(d) 3500 ft
Ans: (c) — 3×10×100 = 3000 ft.
Q40. ILS false glideslope strongest at:
(a) 1.5× nominal
(b) 2× nominal
(c) 3× nominal
(d) 5× nominal
Ans: (c) — False G/S strongest at 3× nominal angle (≈9° for 3° slope).
Q41. ILS LOC DDM on centreline:
(a) Maximum
(b) Zero
(c) Half-scale
(d) 150%
Ans: (b) — On centreline: 90 Hz = 150 Hz → DDM = zero.
Q42. ILS outer marker: tone and light:
(a) 3000 Hz dots, white
(b) 400 Hz dashes, blue
(c) 1300 Hz alt, amber
(d) 400 Hz dashes, amber
Ans: (b) — OM: 400 Hz dashes, blue. MM: 1300 Hz, amber. IM: 3000 Hz, white.
Q43. ILS CAT I minima:
(a) DH 200 ft, RVR 550 m
(b) DH 200 ft, RVR 800 m
(c) DH 100 ft, RVR 400 m
(d) DH 100 ft, RVR 200 m
Ans: (b) — CAT I: DH 200 ft, RVR 800 m.
Q44. ILS CAT II minima:
(a) DH 200 ft, RVR 800 m
(b) DH 100 ft, RVR 400 m
(c) DH 50 ft, RVR 200 m
(d) No DH, RVR 50 m
Ans: (b) — CAT II: DH 100 ft, RVR 400 m.
Q45. ILS CAT IIIC minima:
(a) DH 100 ft, RVR 200 m
(b) DH 50 ft, RVR 75 m
(c) No DH, RVR 50 m
(d) No DH, no RVR minimum
Ans: (d) — CAT IIIC: no DH, no RVR minimum.
Q46. Glideslope bar deflects UP — aircraft is:
(a) Above glidepath
(b) On glidepath
(c) Below glidepath
(d) Left of centreline
Ans: (c) — Bar UP = 150 Hz dominant = aircraft below glidepath — fly up.
Q47. LOC CDI deflects RIGHT — aircraft is:
(a) Right of centreline
(b) Left of centreline
(c) On centreline
(d) Above glidepath
Ans: (b) — CDI right = selected course is right = aircraft is left of centreline — fly right.
Q48. 90 Hz dominant on glideslope — aircraft is:
(a) Above glidepath
(b) Below glidepath
(c) On centreline
(d) Left of LOC
Ans: (a) — 90 Hz dominant on G/S = aircraft above glidepath — fly down.
Q49. ILS marker beacon carrier frequency:
(a) 108 MHz
(b) 75 MHz
(c) 329 MHz
(d) 1090 MHz
Ans: (b) — All ILS markers: 75 MHz carrier.
Q50. ILS 3° G/S at 4.6 NM (50 ft threshold elevation). Height?
(a) 1380 ft
(b) 1400 ft
(c) 1430 ft
(d) 1500 ft
Ans: (c) — 3×4.6×100+50=1380+50=1430 ft.
Q51. ILS back course — CDI sense:
(a) Normal
(b) Reversed
(c) Glideslope only works
(d) No change
Ans: (b) — Back course LOC: CDI sense reversed — fly opposite needle.
Q52. ILS glideslope auto-paired when:
(a) Manually entered on FMC
(b) LOC VHF frequency selected
(c) ILS button pressed on autopilot
(d) Both LOC and GS frequencies entered
Ans: (b) — G/S automatically paired when LOC VHF frequency selected.
Q53. ILS glidepath accuracy requirement:
(a) ±0.5° either side of nominal
(b) ±1.0°
(c) ±0.25°
(d) ±2°
Ans: (a) — G/S accuracy: ±0.5° of nominal slope.
Q54. ILS LOC beam width adjusted to give:
(a) ±2.5° fixed
(b) ±3° fixed
(c) ±35% of runway threshold width
(d) ±5° fixed
Ans: (c) — LOC width: ±35% of threshold width (variable ≈±2°–6°).
Q55. ILS glidepath signal: DDM = 0.175 at:
(a) Course line
(b) Half-scale deflection
(c) Full-scale deflection
(d) False glidepath
Ans: (c) — Full-scale deflection DDM = 0.155. [0.175 may appear in some variants — check exam wording]
Q56. ILS CAT IIIB minima:
(a) DH <50 ft, RVR 50–200 m
(b) No DH, no RVR
(c) DH 100 ft, RVR 200 m
(d) DH 50 ft, RVR 200 m
Ans: (a) — CAT IIIB: DH below 50 ft, RVR 50–200 m.
Q57. Middle marker approximately:
(a) 4–7 NM from threshold
(b) 1050 m from threshold
(c) 300 m from threshold
(d) At decision height point
Ans: (b) — MM: ≈1050 m from threshold.
Q58. ILS number of channels (40-channel system):
(a) 200
(b) 252
(c) 40
(d) 108
Ans: (c) — ILS: 40 channels. MLS: 200. DME: 252.
Q59. ILS LOC emission type:
(a) NON
(b) A9W
(c) F3N
(d) P0N
Ans: (b) — LOC: A9W.
Q60. ILS outer marker located:
(a) 300 m from threshold
(b) 1050 m from threshold
(c) 4–7 NM from threshold
(d) 10 NM from threshold
Ans: (c) — OM: 4–7 NM from threshold.

📡 Radar (Q61–90)

Q61. PRF 400 pps. Maximum radar range:
(a) 162 NM
(b) 200 NM
(c) 203 NM
(d) 240 NM
Ans: (c) — 81,000/400 = 202.5 ≈ 203 NM.
Q62. PRF 250 pps. Max range:
(a) 162 NM
(b) 200 NM
(c) 324 NM
(d) 405 NM
Ans: (c) — 81,000/250 = 324 NM.
Q63. PRF 500 pps. Max range:
(a) 81 NM
(b) 162 NM
(c) 324 NM
(d) 243 NM
Ans: (b) — 81,000/500 = 162 NM.
Q64. Echo received 740 µs after transmission. Range:
(a) 30 NM
(b) 45 NM
(c) 60 NM
(d) 90 NM
Ans: (c) — 740/12.36 = 59.9 ≈ 60 NM.
Q65. Pulse width 2 µs. Minimum range:
(a) 150 m
(b) 300 m
(c) 600 m
(d) 900 m
Ans: (b) — 2×150 = 300 m.
Q66. Pulse width 0.03 µs (ASMI). Minimum range:
(a) 0.45 m
(b) 4.5 m
(c) 45 m
(d) 450 m
Ans: (b) — 0.03×150 = 4.5 m.
Q67. Minimum range determined by:
(a) PRF
(b) Transmitter power
(c) Pulse width
(d) Beamwidth
Ans: (c) — Min range = PW(µs) × 150 m → determined by pulse width.
Q68. Maximum range determined by:
(a) Pulse width
(b) PRF
(c) Beamwidth
(d) Transmitter power
Ans: (b) — Max range = 81,000/PRF → determined by PRF.
Q69. Azimuth resolution improved by:
(a) Wider beam
(b) Narrower beam
(c) Higher PRF
(d) Shorter pulse
Ans: (b) — Better azimuth resolution: narrower beamwidth.
Q70. Radial resolution improved by:
(a) Narrower beam
(b) Shorter pulse width
(c) Higher power
(d) Lower PRF
Ans: (b) — Better radial resolution: shorter pulse width.
Q71. MTI removes:
(a) Second trace returns
(b) Stationary clutter
(c) Rain
(d) Side lobe returns
Ans: (b) — MTI (Moving Target Indication): removes stationary clutter via Doppler.
Q72. Second trace returns removed by:
(a) MTI
(b) Increasing power
(c) Jittering PRF
(d) Reducing beamwidth
Ans: (c) — Second trace returns: jittering (varying) PRF.
Q73. AWR frequency:
(a) 3000 MHz
(b) 9375 MHz
(c) 13300 MHz
(d) 35000 MHz
Ans: (b) — AWR: 9375 MHz (SHF, 3.2 cm).
Q74. AWR is classified as:
(a) Secondary radar
(b) CW radar
(c) Primary radar
(d) Doppler radar
Ans: (c) — AWR: primary radar.
Q75. AWR colour — weakest precipitation:
(a) Magenta
(b) Red
(c) Yellow
(d) Green
Ans: (d) — Weakest: Green (0.7–4 mm/h). Black = nothing.
Q76. AWR colour — turbulence/severe:
(a) Red
(b) Yellow
(c) Green
(d) Magenta
Ans: (d) — Turbulence: Magenta.
Q77. AWR MAP mode uses which beam up to 60–70 NM:
(a) Pencil beam
(b) Cosecant² (fan) beam
(c) Omni
(d) Scanning beam
Ans: (b) — MAP mode: cosecant² fan beam up to 60–70 NM.
Q78. AWR CONT mode shows:
(a) Increased gain
(b) Rainfall rate zone boundaries
(c) Map features
(d) Turbulence only
Ans: (b) — CONT: zone boundaries — steepest gradient = most hazardous.
Q79. AWR HOLD function:
(a) Freezes antenna
(b) Freezes display for storm movement assessment
(c) Holds gain
(d) Holds range
Ans: (b) — HOLD: freezes display to assess storm movement (compare after 2–3 min).
Q80. AWR shadow area:
(a) Area under aircraft
(b) Area behind heavy precipitation
(c) Below the beam
(d) Overhead cone
Ans: (b) — Shadow: region behind heavy rain — attenuated beam reveals nothing beyond.
Q81. AWR hook/U/finger return on display indicates:
(a) Light rain
(b) Snow
(c) Hail and severe turbulence
(d) CAT
Ans: (c) — Hook, U, finger shapes: hail and severe turbulence — avoid.
Q82. AWR stabilisation prevents:
(a) False targets
(b) Multipath
(c) Display distortion during manoeuvres
(d) Second trace returns
Ans: (c) — Stabilisation: prevents display distortion during pitch/roll.
Q83. ASMI scan rate:
(a) 6 rpm
(b) 15 rpm
(c) 60 rpm
(d) 120 rpm
Ans: (c) — ASMI: 60 rpm.
Q84. ASMI purpose:
(a) Long-range surveillance
(b) Aircraft and vehicle surface movement
(c) Weather detection
(d) Approach control
Ans: (b) — ASMI: surface movement — aircraft/vehicles on runways/taxiways.
Q85. Primary radar cannot determine:
(a) Range
(b) Bearing
(c) Identity
(d) Approximate speed (by track)
Ans: (c) — Primary radar: no identity — requires SSR transponder.
Q86. Super-refraction effect on radar:
(a) Reduces range
(b) Extends range beyond LOS
(c) Creates clutter
(d) Increases minimum range
Ans: (b) — Super-refraction: extends range beyond normal LOS (may cause spurious returns).
Q87. PRF 1000 pps. Echo at 1050 µs. Situation:
(a) Target at 85 NM — genuine
(b) Second trace return — actual 85 NM
(c) False target — reject
(d) Target at 4 NM
Ans: (b) — PRI=1000 µs. 1050 > PRI → second trace return. Actual range = 81 + 50/12.36 = 85 NM.
Q88. UK radar separation within 40 NM below FL245:
(a) 1 NM
(b) 2 NM
(c) 3 NM
(d) 5 NM
Ans: (c) — UK radar sep: 3 NM.
Q89. TAR maximum range:
(a) 25 NM
(b) 75 NM
(c) 150 NM
(d) 250 NM
Ans: (b) — TAR (Terminal Area Radar): 75 NM.
Q90. Max PRF for 50 km range:
(a) 330 pps
(b) 617 pps
(c) 3000 pps
(d) 1620 pps
Ans: (c) — PRF = 3×10⁸/(2×50,000) = 3000 pps.

📡 DME (Q91–120)

Q91. DME frequency band:
(a) 108–118 MHz
(b) 329–335 MHz
(c) 960–1215 MHz
(d) 5031–5091 MHz
Ans: (c) — DME: UHF 960–1215 MHz.
Q92. DME transponder offset:
(a) ±21 MHz
(b) ±50 MHz
(c) ±63 MHz
(d) ±100 MHz
Ans: (c) — Ground transponder replies at ±63 MHz from interrogation frequency.
Q93. DME transponder delay:
(a) 12.36 µs
(b) 21 µs
(c) 50 µs
(d) 8 µs
Ans: (c) — Fixed delay: 50 µs. Receiver subtracts before computing range.
Q94. DME tracking phase pulse rate:
(a) 27 ppps
(b) 60 ppps
(c) 150 ppps
(d) 2700 ppps
Ans: (a) — Tracking: 27 ppps.
Q95. DME search phase pulse rate:
(a) 27 ppps
(b) 60 ppps
(c) 150 ppps
(d) 2700 ppps
Ans: (c) — Search: 150 ppps.
Q96. DME saturation approximately:
(a) 27 ppps total
(b) 2700 ppps ≈ 100 aircraft
(c) 60 ppps total
(d) 150 ppps total
Ans: (b) — Saturation: 2700 ppps ≈ 100 aircraft in tracking.
Q97. DME slant range error negligible when:
(a) Range > altitude (NM)
(b) Range (NM) > 3 × altitude (thousands ft)
(c) Always negligible
(d) Below 3000 ft
Ans: (b) — Negligible: Range (NM) > 3 × Alt (000s ft).
Q98. Aircraft at FL180 directly over DME. Display reads:
(a) 0 NM
(b) 0.8 NM
(c) 3 NM
(d) 18 NM
Ans: (c) — 18,000/6076 = 2.96 ≈ 3 NM.
Q99. Time from interrogation to echo = 1300 µs. Range:
(a) 98 NM
(b) 100 NM
(c) 101 NM
(d) 103 NM
Ans: (c) — (1300−50)/12.36 = 1250/12.36 = 101.1 NM.
Q100. DME number of channels:
(a) 40
(b) 108
(c) 200
(d) 252
Ans: (d) — DME: 252 channels.
Q101. DME emission type:
(a) A9W
(b) P0N
(c) F3N
(d) NON
Ans: (b) — DME: P0N (pulsed, no info modulation).
Q102. VOR/DME pairing outside TMA — DME within:
(a) 100 ft
(b) 1 NM
(c) 2000 ft
(d) 2 NM
Ans: (c) — Outside TMA: DME within 2000 ft of VOR for auto-pairing.
Q103. VOR/DME pairing inside TMA — DME within:
(a) 100 ft
(b) 1 NM
(c) 2000 ft
(d) 2 NM
Ans: (a) — Inside TMA: DME within 100 ft of VOR.
Q104. DME jittered pulse pairs — purpose:
(a) Higher power
(b) Avoid ILS interference
(c) Identify own replies
(d) Increase range
Ans: (c) — Jittered pairs: aircraft identifies its own replies by consistent time offset.
Q105. DME squitter purpose:
(a) Ident
(b) Fill capacity to prevent aircraft re-entering search
(c) Range calibration
(d) Interference avoidance
Ans: (b) — Squitter: fills unused transponder capacity so aircraft detect station is active.
Q106. DME memory duration in tracking:
(a) 5 s
(b) 10 s
(c) 15 s
(d) 30 s
Ans: (b) — DME memory: 10 seconds.
Q107. DME/P accuracy:
(a) ±0.5 NM
(b) ±1 NM
(c) ±100 ft
(d) ±50 m
Ans: (c) — DME/P (Precision): ±100 ft for MLS CAT II/III.
Q108. DME/P used with:
(a) ILS
(b) MLS
(c) GBAS
(d) SBAS
Ans: (b) — DME/P used with MLS.
Q109. VORTAC: military aircraft uses:
(a) VOR bearing only
(b) VOR bearing + TACAN DME
(c) TACAN bearing + TACAN DME
(d) VOR only
Ans: (c) — Military at VORTAC: TACAN bearing + TACAN DME.
Q110. DME ident interval:
(a) Every 10 s
(b) Every 30 s
(c) Continuous
(d) Every 60 s
Ans: (b) — DME ident: every 30 seconds, 1350 Hz Morse.
Q111. DME type of radar:
(a) Primary
(b) Secondary
(c) Doppler
(d) CW
Ans: (b) — DME: secondary radar principle.
Q112. RNAV DME range shown to:
(a) Real DME station
(b) Phantom station (waypoint)
(c) Nearest airport
(d) FIX position
Ans: (b) — RNAV DME: shows distance to phantom station (waypoint).
Q113. DME en-route accuracy:
(a) ±0.25 NM
(b) ±0.5 NM or ±3% (whichever greater)
(c) ±1 NM
(d) ±2%
Ans: (b) — DME accuracy: ±0.5 NM or ±3%, whichever greater.
Q114. GPS system uses what type of ranging?
(a) Secondary radar (2-way)
(b) One-way passive ranging
(c) Primary radar
(d) DME-type 2-way
Ans: (b) — GPS: one-way passive — satellite broadcasts, receiver measures time of arrival.
Q115. DME acquisition phase rate:
(a) 27 ppps
(b) 60 ppps
(c) 150 ppps
(d) 2700 ppps
Ans: (b) — Acquisition: 60 ppps.
Q116. Aircraft at 5000 ft AGL over DME. Slant range reads:
(a) 0 NM
(b) 0.82 NM
(c) 2 NM
(d) 5 NM
Ans: (b) — 5000/6076 = 0.82 NM.
Q117. DME squitter pulse rate (total with squitter):
(a) 27 ppps
(b) 2700 ppps
(c) 150 ppps
(d) 60 ppps
Ans: (b) — With squitter: maintained at 2700 ppps.
Q118. Which PRN codes does GPS L1 carry?
(a) P-code only
(b) C/A and P-code
(c) C/A code only (civil)
(d) SPS only
Ans: (b) — L1 (1575.42 MHz): carries both C/A code (civil) and P-code (military).
Q119. DME ground transponder delay ensures:
(a) Collision avoidance
(b) Positive identification of own replies
(c) Positive time offset for range calculation
(d) Synchronisation with VOR
Ans: (c) — 50 µs delay ensures receiver always has positive elapsed time to subtract and compute range.
Q120. DME interrogation spacing (pulse pair):
(a) 6 µs X-channel; 12 µs Y-channel
(b) 12 µs X; 36 µs Y
(c) Random (jittered)
(d) Fixed at 12 µs
Ans: (b) — X-channel pair spacing: 12 µs. Y-channel: 36 µs.

📡 SSR (Q121–150)

Q121. SSR interrogation frequency:
(a) 1030 MHz
(b) 1090 MHz
(c) 960 MHz
(d) 1215 MHz
Ans: (a) — Ground interrogates on 1030 MHz.
Q122. SSR transponder reply frequency:
(a) 1030 MHz
(b) 1090 MHz
(c) 960 MHz
(d) 1215 MHz
Ans: (b) — Aircraft replies on 1090 MHz.
Q123. Mode A P1–P3 spacing:
(a) 8 µs
(b) 17 µs
(c) 21 µs
(d) 25 µs
Ans: (a) — Mode A: 8 µs.
Q124. Mode C P1–P3 spacing:
(a) 8 µs
(b) 17 µs
(c) 21 µs
(d) 25 µs
Ans: (c) — Mode C: 21 µs.
Q125. Mode A codes available:
(a) 256
(b) 4096
(c) 65,536
(d) 16,777,216
Ans: (b) — Mode A: 4096 (octal 0000–7777).
Q126. Mode S ICAO address size:
(a) 12 bit
(b) 16 bit
(c) 24 bit
(d) 32 bit
Ans: (c) — Mode S: 24-bit address → 16.7 million unique codes.
Q127. Mode C altitude resolution:
(a) 100 ft
(b) 50 ft
(c) 25 ft
(d) 10 ft
Ans: (a) — Mode C: 100 ft increments. Mode S: 25 ft.
Q128. Squawk 7700:
(a) Hijack
(b) Radio failure
(c) Emergency
(d) VFR
Ans: (c) — 7700 = Emergency.
Q129. Squawk 7600:
(a) Emergency
(b) Radio failure
(c) Hijack
(d) Military
Ans: (b) — 7600 = Radio failure (NORDO).
Q130. Squawk 7500:
(a) Emergency
(b) Radio failure
(c) Unlawful interference/hijack
(d) VFR conspicuity
Ans: (c) — 7500 = Hijack/unlawful interference.
Q131. Garbling occurs when two aircraft within:
(a) 0.5 NM
(b) 1.7 NM same direction
(c) 3 NM
(d) 5 NM
Ans: (b) — Garbling: 1.7 NM in same direction from radar.
Q132. Fruiting caused by:
(a) Garbling
(b) Replies to other ground interrogators
(c) Multipath
(d) SA
Ans: (b) — Fruiting: aircraft replies to other stations' interrogations → phantom targets.
Q133. IDENT button — SPI duration:
(a) 10 s
(b) 20 s
(c) 30 s
(d) 60 s
Ans: (b) — SPI: 20 seconds.
Q134. SLS — P2 pulse is:
(a) Directional, same as P1
(b) Omnidirectional
(c) Higher power than P1
(d) On 1090 MHz
Ans: (b) — SLS P2: omnidirectional → if P2>P1, transponder suppresses reply (side lobe).
Q135. ISLS purpose:
(a) Prevent garbling
(b) Synchronise multiple interrogators to prevent fruiting
(c) Improve altitude reporting
(d) Enable data link
Ans: (b) — ISLS: synchronises multiple ground SSR stations → prevents fruiting.
Q136. Transponder STANDBY:
(a) Reduced power response
(b) No response to interrogations
(c) Mode C only
(d) Mode S only
Ans: (b) — STANDBY: energised, will NOT respond.
Q137. UK VFR conspicuity squawk:
(a) 2000
(b) 7000
(c) 7700
(d) 1200
Ans: (b) — UK VFR: 7000.
Q138. Mode S advantage:
(a) VHF frequencies
(b) Selective addressing — eliminates garbling
(c) No transponder needed
(d) No LOS needed
Ans: (b) — Mode S: selective addressing by unique 24-bit ICAO code.
Q139. ADS-B squitter interval:
(a) 1 s
(b) 0.5 s
(c) 2 s
(d) 10 s
Ans: (b) — ADS-B: every 0.5 seconds.
Q140. Mode C altitude referenced to:
(a) QNH
(b) QFE
(c) 1013.25 hPa
(d) Local QNH
Ans: (c) — Mode C: always 1013.25 hPa.
Q141. SSR reply framing pulses F1–F2 spacing:
(a) 8 µs
(b) 12 µs
(c) 20.3 µs
(d) 50 µs
Ans: (c) — F1–F2: 20.3 µs.
Q142. ACAS/TCAS uses:
(a) Mode A
(b) Mode C
(c) Mode S
(d) All modes
Ans: (c) — TCAS: uses Mode S 1030/1090 MHz for A/C-to-A/C interrogation.
Q143. ELS (Elementary Surveillance) provides:
(a) Squawk and altitude
(b) Squawk, flight ID, altitude, emergency
(c) Full EHS data
(d) GPS position
Ans: (b) — ELS: squawk, callsign, pressure altitude, emergency.
Q144. EHS (Enhanced Surveillance) adds:
(a) Nothing over ELS
(b) Selected altitude, airspeed, magnetic heading
(c) GPS position
(d) TCAS data
Ans: (b) — EHS adds: selected altitude, airspeed, magnetic heading.
Q145. Squawk 2000 means:
(a) Emergency
(b) Entering CAS without clearance
(c) Military
(d) Radio failure
Ans: (b) — 2000: entering CAS without prior ATC clearance.
Q146. SSR antenna location:
(a) Separate tower
(b) On top of primary radar, co-rotating
(c) Inside fuselage
(d) Alongside ILS building
Ans: (b) — SSR antenna: mounted on top of primary radar, co-rotating.
Q147. Mode S data link direction:
(a) Downlink only
(b) Uplink only
(c) Bidirectional
(d) No data link
Ans: (c) — Mode S: bidirectional (downlink + uplink).
Q148. Transponder ALT mode:
(a) Responds Mode A only
(b) Responds Mode A + C (altitude)
(c) Mode S only
(d) STANDBY
Ans: (b) — ALT mode: responds to Mode A and Mode C.
Q149. ADS-B position source:
(a) SSR ranging
(b) DME
(c) GPS
(d) Transponder timing
Ans: (c) — ADS-B: broadcasts GPS-derived position via 1090 MHz extended squitter.
Q150. Minimum range for no garbling:
(a) 0.5 NM
(b) 1.7 NM
(c) 3 NM
(d) 5 NM
Ans: (b) — No garbling when separation > 1.7 NM in same direction.

📡 AWR / MLS (Q151–180)

Q151. AWR wavelength:
(a) 1 cm
(b) 3.2 cm
(c) 10 cm
(d) 23 cm
Ans: (b) — AWR: 3.2 cm (9375 MHz).
Q152. AWR MAN mode beam:
(a) Fan beam at all ranges
(b) Pencil beam, manual gain
(c) Omni
(d) Fan beam beyond 70 NM
Ans: (b) — MAN: pencil beam, manual gain.
Q153. AWR cannot detect:
(a) Thunderstorms
(b) Hail
(c) CAT
(d) Heavy rain
Ans: (c) — AWR cannot detect CAT (Clear Air Turbulence) — no precipitation.
Q154. AWR tilt positive (+) means:
(a) Beam below horizontal
(b) Beam above horizontal
(c) No tilt
(d) Gain increased
Ans: (b) — Positive tilt = beam above horizontal.
Q155. AWR: rain shadow risk is:
(a) Light rain conceals nothing
(b) Heavy rain attenuates beam — severe weather beyond may be hidden
(c) Snow creates shadow
(d) Shadow only below aircraft
Ans: (b) — Rain shadow: severe weather may be hidden behind heavy precipitation.
Q156. AWR 'finger' return shape indicates:
(a) Light rain
(b) Hail/severe turbulence
(c) Snow
(d) CAT
Ans: (b) — Finger shape: hail and severe turbulence.
Q157. AWR scalloped edges on return indicate:
(a) Ground return
(b) Hail
(c) Light rain
(d) Icing
Ans: (b) — Scalloped edges: hail.
Q158. AWR AGC/STC range:
(a) Up to 25 NM
(b) All ranges
(c) Beyond 70 NM
(d) First 5 NM only
Ans: (a) — STC (Swept Gain/AGC): equalises returns up to ≈25 NM.
Q159. AWR stabilisation failure — display effect:
(a) Blanks
(b) Lopsided during bank/pitch
(c) Gains increase
(d) Range rings disappear
Ans: (b) — Stabilisation failure: display becomes lopsided during manoeuvres.
Q160. MLS frequency band:
(a) VHF 108–118 MHz
(b) UHF 329–335 MHz
(c) SHF 5031–5090.7 MHz
(d) UHF 960–1215 MHz
Ans: (c) — MLS: SHF 5031–5090.7 MHz.
Q161. MLS azimuth coverage:
(a) ±20°
(b) ±35°
(c) ±40°
(d) ±60°
Ans: (c) — MLS azimuth: ±40° of centreline.
Q162. MLS channels:
(a) 40
(b) 100
(c) 200
(d) 252
Ans: (c) — MLS: 200 channels.
Q163. MLS principle:
(a) DDM like ILS
(b) TRSB — time between TO/FRO sweeps
(c) Phase comparison
(d) Doppler
Ans: (b) — MLS: TRSB (Time Referenced Scanning Beam).
Q164. MLS glide slope range:
(a) Fixed 3°
(b) 0.9° to 20°
(c) 2° to 10°
(d) Fixed 5°
Ans: (b) — MLS G/S: 0.9° to 20° selectable.
Q165. MLS ident prefix letter:
(a) I
(b) M
(c) V
(d) D
Ans: (b) — MLS ident: prefix M.
Q166. MLS range measurement:
(a) Pulse echo timing
(b) DME/P built-in
(c) Phase comparison
(d) Doppler
Ans: (b) — MLS range: DME/P (±100 ft accuracy).
Q167. MLS advantage over ILS — azimuth coverage:
(a) ±35° same as ILS
(b) ±40° vs ±35°
(c) 360°
(d) ±20°
Ans: (b) — MLS: ±40° vs ILS ±35°.
Q168. MLS UK usable range:
(a) 10 NM
(b) 15 NM
(c) 20 NM
(d) 35 NM
Ans: (c) — MLS UK: 20 NM.
Q169. AWR U-shape return:
(a) Light rain
(b) Hail/turbulence
(c) Snow
(d) CAT
Ans: (b) — U-shape: hail and turbulence.
Q170. AWR MAP mode optimal up to:
(a) 25 NM
(b) 60–70 NM
(c) 150 NM
(d) All ranges
Ans: (b) — MAP (cosecant² beam): up to 60–70 NM.
Q171. ASMI frequency band:
(a) 3 GHz
(b) 9.375 GHz
(c) 15–17 GHz
(d) 35 GHz
Ans: (c) — ASMI: 15–17 GHz (SHF, ≈2 cm).
Q172. AWR WEA colour for no precip:
(a) Green
(b) Yellow
(c) Red
(d) Black
Ans: (d) — No precipitation: Black.
Q173. AWR hook return on display:
(a) Light drizzle
(b) Hail/severe turbulence
(c) CAT
(d) Snow
Ans: (b) — Hook shape: hail/severe turbulence.
Q174. AWR ageing (HOLD) — how long before compare?
(a) 30 s
(b) 1 min
(c) 2–3 min
(d) 10 min
Ans: (c) — Deselect HOLD after 2–3 minutes — compare images for storm movement.
Q175. AWR pencil beam — used in MAN mode beyond:
(a) 25 NM
(b) 50 NM
(c) 60–70 NM
(d) 150 NM
Ans: (c) — Pencil beam (MAN) for weather beyond 60–70 NM.
Q176. AWR — recommended tilt when far from storm cell:
(a) Tilt down to surface
(b) Zero tilt
(c) Tilt up
(d) Reduce gain
Ans: (c) — Far from cell: tilt up to see tops — determines storm height/severity.
Q177. SSR transponder receives on ___, replies on ___:
(a) 1090, 1030
(b) 1030, 1090
(c) 960, 1215
(d) 1215, 960
Ans: (b) — RX: 1030 MHz, TX: 1090 MHz.
Q178. EGNOS is classified as:
(a) LAAS
(b) GBAS
(c) SBAS
(d) RAIM
Ans: (c) — EGNOS: SBAS (Satellite Based Augmentation System).
Q179. LAAS/GBAS transmits corrections via:
(a) Satellite
(b) HF radio
(c) VHF data link
(d) UHF beacon
Ans: (c) — LAAS/GBAS: VHF data link.
Q180. SBAS — corrections transmitted via:
(a) Dedicated HF stations
(b) Geostationary satellites
(c) VHF data link
(d) L-band beacons
Ans: (b) — SBAS: corrections via geostationary satellites.

📡 GNSS / RNAV / Mixed (Q181–243)

Q181. B-RNAV required accuracy:
(a) ±1 NM, 95%
(b) ±5 NM, 95%
(c) ±5 NM, 90%
(d) ±2 NM, 95%
Ans: (b) — B-RNAV: ±5 NM on 95% of occasions.
Q182. P-RNAV required accuracy:
(a) ±1 NM, 95%
(b) ±5 NM, 95%
(c) ±0.5 NM, 95%
(d) ±2 NM, 90%
Ans: (a) — P-RNAV: ±1 NM on 95% of occasions.
Q183. FMC navigation database update cycle:
(a) 7 days
(b) 14 days
(c) 28 days (AIRAC)
(d) 90 days
Ans: (c) — FMC nav DB: 28 days (AIRAC cycle).
Q184. RNAV erratic: aircraft beyond LOS of reference VOR/DME:
(a) True
(b) False
(c) Only in TMA
(d) Only in cone of confusion
Ans: (a) — Yes — beyond LOS or DOC of reference VOR/DME → erratic RNAV.
Q185. GPS horizontal accuracy (SPS, 95%):
(a) ±100 m
(b) ±22 m
(c) ±13 m
(d) ±50 m
Ans: (c) — Horizontal: ±13 m (95%).
Q186. GPS vertical accuracy (SPS, 95%):
(a) ±13 m
(b) ±22 m
(c) ±50 m
(d) ±100 m
Ans: (b) — Vertical: ±22 m (95%).
Q187. GPS time accuracy (SPS, 95%):
(a) 1 µs
(b) 40 ns
(c) 100 ns
(d) 1 ms
Ans: (b) — Time: 40 nanoseconds (95%).
Q188. GPS — why pseudo-range not true range?
(a) Ionospheric delay
(b) Receiver clock error not yet eliminated
(c) SA applied
(d) Multipath
Ans: (b) — Pseudo-range: uncorrected for receiver clock error.
Q189. GPS minimum SVs for 3D fix + time:
(a) 3
(b) 4
(c) 5
(d) 6
Ans: (b) — 4 SVs for 3D fix (lat, lon, alt, time).
Q190. GPS RAIM — SVs for fault detection only:
(a) 4
(b) 5
(c) 6
(d) 7
Ans: (b) — RAIM detection: 5 SVs.
Q191. GPS RAIM — SVs for fault exclusion:
(a) 4
(b) 5
(c) 6
(d) 7
Ans: (c) — RAIM exclusion: 6 SVs.
Q192. GPS orbital height:
(a) 19,099 km
(b) 20,180 km
(c) 23,222 km
(d) 35,800 km
Ans: (b) — GPS: 20,180 km.
Q193. GPS orbital inclination:
(a) 55°
(b) 56°
(c) 63°
(d) 65°
Ans: (a) — GPS: 55° inclination.
Q194. GPS orbital period:
(a) 24 h
(b) 12 h
(c) 11 h 56 min
(d) 11 h 15 min
Ans: (c) — GPS: 11 h 56 min.
Q195. GPS L1 frequency:
(a) 1227.6 MHz
(b) 1575.42 MHz
(c) 1602 MHz
(d) 1246 MHz
Ans: (b) — GPS L1: 1575.42 MHz.
Q196. GPS L2 frequency:
(a) 1227.6 MHz
(b) 1575.42 MHz
(c) 1602 MHz
(d) 1246 MHz
Ans: (a) — GPS L2: 1227.6 MHz.
Q197. GPS geoid reference:
(a) PZ90
(b) ETRS89
(c) WGS84
(d) GRS80
Ans: (c) — GPS: WGS84.
Q198. GLONASS geoid reference:
(a) WGS84
(b) PZ90
(c) ETRS89
(d) GRS80
Ans: (b) — GLONASS: PZ90.
Q199. Galileo geoid reference:
(a) WGS84
(b) PZ90
(c) ETRS89
(d) GRS80
Ans: (c) — Galileo: ETRS89.
Q200. GLONASS orbital inclination:
(a) 55°
(b) 56°
(c) 63.4°
(d) 65°
Ans: (d) — GLONASS: 65°.
Q201. GLONASS orbital period:
(a) 11 h 56 min
(b) 11 h 15 min
(c) 12 h
(d) 14 h 8 min
Ans: (b) — GLONASS: 11 h 15 min.
Q202. Galileo orbital height:
(a) 20,180 km
(b) 19,099 km
(c) 23,222 km
(d) 35,800 km
Ans: (c) — Galileo: 23,222 km.
Q203. GPS almanac used by receiver to:
(a) Determine SA
(b) Compute position
(c) Identify which SVs visible
(d) Correct clock error
Ans: (c) — Almanac: receiver determines which SVs are above horizon for faster acquisition.
Q204. GPS ephemeris — sub-frames:
(a) 1
(b) 2 and 3
(c) 4 and 5
(d) 5
Ans: (b) — Ephemeris data: sub-frames 2 and 3.
Q205. GPS navigation message transmitted at:
(a) 50 Hz
(b) 1 kHz
(c) 9960 Hz
(d) 1575 MHz
Ans: (a) — Nav message: 50 Hz (50 bps) modulation on L1 and L2.
Q206. GNSS altitude cannot be used alone for DH/MDA because:
(a) GPS too inaccurate
(b) WGS84 ellipsoid differs from geoid (MSL) by up to 50 m
(c) Update rate too slow
(d) ILS always more accurate
Ans: (b) — WGS84 ellipsoid ≠ MSL geoid → difference up to 50 m.
Q207. SBAS geostationary orbit altitude:
(a) 20,180 km
(b) 19,099 km
(c) 23,222 km
(d) 35,800 km
Ans: (d) — Geostationary: 35,800 km.
Q208. GPS dual-frequency advantage:
(a) Higher power
(b) Eliminates ≈99% ionospheric error
(c) Better coverage
(d) Faster acquisition
Ans: (b) — Dual-frequency (L1+L2): eliminates ≈99% of ionospheric error.
Q209. GPS integrity warning time (non-precision approach):
(a) 2 s
(b) 8 s
(c) 30 s
(d) 10 s
Ans: (b) — Non-precision: 8 seconds. Precision (CAT I): 6 s. ILS equivalent: 2 s.
Q210. 4D RNAV adds to 3D capability:
(a) Vertical guidance
(b) GPS
(c) Timing (RTA)
(d) TCAS
Ans: (c) — 4D RNAV: lateral + vertical + timing (RTA).
Q211. FMC auto-tunes DMEs for:
(a) Nearest station
(b) Pilot's selection
(c) Best geometry (angle of cut)
(d) Highest power stations
Ans: (c) — FMC selects DMEs for best angle of cut.
Q212. External input to FMC:
(a) INS
(b) Pressure altitude
(c) Compass
(d) VOR/DME
Ans: (d) — External (ground-based): VOR/DME.
Q213. ADC input to FMC:
(a) Heading
(b) Groundspeed
(c) TAS
(d) Position
Ans: (c) — ADC provides: TAS, pressure altitude, SAT.
Q214. RNAV course line computer function:
(a) Direct to VOR/DME facility
(b) Rho/theta → track and distance to waypoint
(c) ILS approach guidance
(d) TCAS alerting
Ans: (b) — RNAV: uses rho/theta to compute track + distance to phantom waypoint.
Q215. GPS range measurement: time measured from:
(a) Receiver to SV and back
(b) SV to receiver (one-way)
(c) Control segment to SV
(d) SV to control segment
Ans: (b) — GPS: one-way time from SV to receiver.
Q216. GPS number of orbital planes:
(a) 3
(b) 4
(c) 6
(d) 8
Ans: (c) — GPS: 6 orbital planes, 4 SVs each = 24 SVs.
Q217. GLONASS number of orbital planes:
(a) 3
(b) 4
(c) 6
(d) 8
Ans: (a) — GLONASS: 3 orbital planes, 8 SVs each = 24 SVs.
Q218. Galileo number of orbital planes:
(a) 3
(b) 4
(c) 6
(d) 8
Ans: (a) — Galileo: 3 orbital planes, 10 SVs each = 30 SVs.
Q219. GPS C/A code chipping rate:
(a) 1.023 MHz
(b) 10.23 MHz
(c) 50 Hz
(d) 9960 Hz
Ans: (a) — C/A code: 1.023 MHz. P-code: 10.23 MHz.
Q220. Selective Availability (SA):
(a) Still active on civilian GPS
(b) Intentional degradation of SPS; switched off in 2000
(c) Used only by military
(d) Replaced by RAIM
Ans: (b) — SA: switched off 2 May 2000. No longer applied.
Q221. RNAV erratic most likely cause:
(a) Cone of confusion of phantom
(b) Beyond DOC/LOS of reference VOR/DME
(c) FMC failure
(d) INS drift
Ans: (b) — Most likely: beyond DOC or LOS of reference VOR/DME.
Q222. P-RNAV accuracy requirement:
(a) ±5 NM, 95%
(b) ±1 NM, 95%
(c) ±0.5 NM, 95%
(d) ±1 NM, 99%
Ans: (b) — P-RNAV: ±1 NM, 95%.
Q223. Multi-sensor FMC + GPS discrepancy — action:
(a) Trust GPS
(b) Trust multi-sensor; display multi-sensor output
(c) Select nearest VOR
(d) Declare emergency
Ans: (b) — Discrepancy: trust multi-sensor; GPS may have failed.
Q224. GBAS/LAAS accuracy for CAT I:
(a) ±16 m horizontal, ±6 m vertical
(b) ±100 ft
(c) ±0.5 NM
(d) Same as ILS
Ans: (a) — GBAS CAT I: ±16 m horizontal, ±6 m vertical (95%).
Q225. GPS constellation: total operational SVs:
(a) 21
(b) 24
(c) 27
(d) 30
Ans: (b) — GPS: 24 SVs (operational); up to 32 with spares.
Q226. GALILEO constellation: total SVs:
(a) 24
(b) 27
(c) 30
(d) 32
Ans: (c) — Galileo: 30 SVs.
Q227. GLONASS constellation:
(a) 21
(b) 24
(c) 27
(d) 30
Ans: (b) — GLONASS: 24 SVs.
Q228. GPS PRN codes — how many available?
(a) 24
(b) 32
(c) 64
(d) 252
Ans: (b) — GPS PRN codes: 32 available (SVs numbered PRN 1–32).
Q229. GNSS integrity definition:
(a) Accuracy of the position solution
(b) Ability to alert users when system should not be used
(c) Number of SVs visible
(d) Signal continuity
Ans: (b) — Integrity: ability to provide timely warning when system unfit for navigation.
Q230. RAIM — what does it detect?
(a) Ionospheric error
(b) Failed SV causing position error exceeding limits
(c) Multipath
(d) Clock drift in receiver
Ans: (b) — RAIM detects: failed SV causing excessive position error.
Q231. GPS almanac download time:
(a) 30 s
(b) 12.5 min
(c) 30 min
(d) 1 hour
Ans: (b) — Full almanac download: 12.5 minutes (25 frames × 30 s).
Q232. GPS cold start — time to first fix:
(a) 30 s
(b) 1–2 min
(c) 12.5 min
(d) Up to 30 min
Ans: (c) — Cold start (no almanac): up to 12.5 min for almanac download.
Q233. PDOP (Position Dilution of Precision) — best geometry:
(a) High PDOP
(b) Low PDOP
(c) PDOP = 1 always
(d) PDOP irrelevant
Ans: (b) — Best geometry: low PDOP (SVs spread widely across sky).
Q234. GPS ionospheric model corrects approximately:
(a) 10%
(b) 50%
(c) 75%
(d) 99%
Ans: (b) — GPS ionospheric model: ≈50% correction. Dual-freq: ≈99%.
Q235. SBAS integrity monitoring provided by:
(a) Ground reference stations
(b) Control segment only
(c) RAIM
(d) Aircraft receiver
Ans: (a) — SBAS: network of ground reference stations monitors satellite integrity.
Q236. Galileo orbital inclination:
(a) 55°
(b) 56°
(c) 63°
(d) 65°
Ans: (b) — Galileo: 56°.
Q237. GPS Week Number rollover issue — period:
(a) 10.9 years (1024 weeks)
(b) 19.7 years
(c) 7 years
(d) Every year
Ans: (a) — GPS week: 10-bit number → rolls over every 1024 weeks (≈19.7 years). [Some say 19.7 — check ICAO doc for exact value used]
Q238. GNSS continuity of service — definition:
(a) System accuracy
(b) Probability of system performing without interruption during operation
(c) Integrity
(d) Number of SVs
Ans: (b) — Continuity: probability of uninterrupted operation during intended use.
Q239. GNSS availability — definition:
(a) Accuracy spec
(b) Proportion of time system provides navigation with required accuracy
(c) Integrity
(d) Continuity
Ans: (b) — Availability: proportion of time system meets accuracy and integrity requirements.
Q240. GPS L1 C/A code — chip length:
(a) 30 m
(b) 300 m
(c) 1 km
(d) 3 km
Ans: (b) — C/A chip length = c/f = 3×10⁸/1.023×10⁶ = 293 m ≈ 300 m.
Q241. GNSS approach — LPV (Localizer Performance with Vertical guidance) provides:
(a) Lateral only
(b) Lateral + baro-VNAV
(c) Lateral + SBAS vertical guidance (like ILS CAT I)
(d) No approach minima
Ans: (c) — LPV: SBAS approach with lateral + SBAS vertical guidance, minima approaching CAT I.
Q242. GPS time offset from UTC at receiver:
(a) Zero — GPS = UTC
(b) GPS ahead of UTC by integer seconds (leap seconds)
(c) GPS behind UTC
(d) Varies daily
Ans: (b) — GPS time: ahead of UTC by integer leap seconds. Receiver subtracts leap second count to display UTC.
Q243. GNSS — which error source causes errors of hundreds of metres without correction?
(a) Multipath
(b) Clock error
(c) Selective Availability (when active)
(d) Tropospheric delay
Ans: (c) — When SA active: errors up to 100 m (horizontal). SA now off.
📝 66-Question Specimen Exam — Answer Key
Q1=b • Q2=c • Q3=d • Q4=a • Q5=a • Q6=d • Q7=b • Q8=c • Q9=a • Q10=c • Q11=d • Q12=d
Q13=c • Q14=a • Q15=d • Q16=a • Q17=d • Q18=b • Q19=a • Q20=b • Q21=c • Q22=d • Q23=b • Q24=d
Q25=a • Q26=d • Q27=b • Q28=c • Q29=b • Q30=a • Q31=a • Q32=a • Q33=b • Q34=c • Q35=a • Q36=d
Q37=b • Q38=a • Q39=b • Q40=b • Q41=d • Q42=b • Q43=b • Q44=b • Q45=c • Q46=a • Q47=d • Q48=a
Q49=c • Q50=c • Q51=b • Q52=d • Q53=b • Q54=a • Q55=a • Q56=a • Q57=a • Q58=c • Q59=d • Q60=b
Q61=b • Q62=c • Q63=b • Q64=a • Q65=b • Q66=b
© Capt Pankaj Pahil | www.ghostaviator.com
DGCA CPL/ATPL Radio Navigation Study Notes
Chapter 19 — Revision Questions (243 Q)
Capt Pankaj Pahil | www.ghostaviator.com
For personal study use only.