ILSRadio Navigation — DGCA CPL practice questions
Question 1 of 14
The coverage of an ILS localizer extends to ___ either side of the on-course line out to a range of ___ NM.
All 14 questions — ILS
Radio Navigation · DGCA CPL. The correct option is marked on each.
Q1. The coverage of an ILS localizer extends to ___ either side of the on-course line out to a range of ___ NM.
- A.10°, 35
- B.35°, 10
- C.35°, 17✓
- D.25°, 25
Why: Localizer: 35° from centreline out to 17 NM ; ±10° out to 25 NM. The coverage narrows to 17 NM within the wider ±35° sector.
Q2. The upper and lower limits of an ILS glide path transmitter having a 3.5° glide slope are:
- A.6.125° – 1.575°✓
- B.7.700° – 1.225°
- C.5.250° – 1.350°
- D.3.850° – 3.150°
Why: Upper = 1.75 × 3.5° = 6.125° ; Lower = 0.45 × 3.5° = 1.575° .
Q3. The minimum angle at which a false glide path is likely to be encountered on a 3° glide path is:
- A.6 degrees✓
- B.5.35 degrees
- C.normal glide slope times 1.75
- D.normal glide slope times 0.70
Why: First false GP ≈ twice the true GP angle = 2 × 3° = 6° . False GPs always occur above the true glide slope.
Q4. The visual and aural indications when overflying an ILS middle marker are:
- A.continuous low pitched dashes with blue light
- B.continuous high pitched dots with amber light
- C.alternating medium pitch dots and dashes with amber light✓
- D.one Morse letter with white light
Why: MM = Amber light + alternating dots and dashes at 3 per second + 1300 Hz medium pitch audio.
Q5. An aircraft on ILS approach is receiving stronger 150 Hz signals than 90 Hz. Correct actions to reach centreline and glide path:
- A.DOWN and LEFT
- B.UP and LEFT✓
- C.UP and RIGHT
- D.DOWN and RIGHT
Why: Stronger 150 Hz on localizer = aircraft in RIGHT (blue) lobe = aircraft is RIGHT of centreline → fly LEFT . Stronger 150 Hz on GP = aircraft BELOW glide slope (lower lobe = 150 Hz) → fly UP . Combined: UP and LEFT .
Q6. Upper and lower limits of ILS glide path with 3.0° glide slope:
- A.0.35° / 0.70°
- B.3.00° / at least 6°
- C.5.25° / 1.35°✓
- D.10.0° / 35.0°
Why: Upper = 1.75 × 3° = 5.25° ; Lower = 0.45 × 3° = 1.35° .
Q7. A category II ILS installation in the UK:
- A.provides accurate guidance down to 50 ft above the horizontal plane containing the runway threshold✓
- B.has a steep glide path, normally 7.5°
- C.provides guidance to and along the runway surface
- D.has a false glide path exactly twice the true GP angle
Why: Cat II ILS ground installation provides guidance to the point where the glide path intersects at 50 ft (15 m) above the threshold horizontal plane.
Q8. Which ILS indicator shows aircraft on final approach left of centreline and at maximum safe deviation below the glide path?
- A.(a) — bar right, GP needle centred
- B.(b) — bar left, GP needle high
- C.(c) — bar centred, GP needle centred
- D.(d) — bar right, GP needle high (fly up) at 2.5 dots✓
Why: Aircraft LEFT of centreline → localizer bar deflects RIGHT . Below glide path at maximum safe deviation (2.5 dots fly up) → GP needle shows fly up, 2.5 dots . This is option (d).
Q9. An aircraft tracking to intercept the ILS localizer inbound but outside the published coverage angle:
- A.will receive false on-course or reverse sense signals✓
- B.will not normally receive signals
- C.will receive signals without coding
- D.can expect correct indications
Why: Outside the coverage sectors, the ILS may give false on-course or reverse sense signals . The signal exists outside the protected coverage area but cannot be guaranteed to give correct guidance.
Q10. The outer marker of an ILS has visual identification of:
- A.alternating dots and dashes on a blue light
- B.continuous dots at 3 per second, blue light
- C.continuous dashes at 2 per second, amber light
- D.continuous dashes at 2 per second, blue light✓
Why: OM = Blue light + 2 dashes per second (400 Hz, low pitch).
Q11. The specified maximum safe fly-up indication on a 5-dot CDI is:
- A.half full scale deflection above centreline
- B.2.5 dots fly up✓
- C.just before full scale deflection
- D.1.3 dots fly up
Why: Maximum safe deviation below glide slope = 2.5 dots fly up (half the 5-dot full scale). Beyond this, initiate immediate go-around as terrain clearance may be compromised.
Q12. An aircraft using ILS outside coverage sectors — which is correct?
- A.Glide slope false course, localizer intermittent
- B.No transmissions, OFF flags visible
- C.Localizer false course, glide slope reverse sense
- D.Localizer false course/reverse sense; glide slope intermittent/incorrect✓
Why: Outside coverage: localizer may give false on-course and reverse sense indications ; glide slope may give intermittent and incorrect indications . Answer (d) correctly states this combination.
Q13. Coverage of ILS glide slope in azimuth:
- A.±8° out to 10 NM✓
- B.±10° out to 8 NM
- C.±12° out to 17 NM
- D.±35° out to 25 NM
Why: GP horizontal coverage: ±8° azimuth out to at least 10 NM .
Q14. ILS receivers showing predominant 90 Hz on both localizer and glide slope; runway QDM 264°. Aircraft is:
- A.north of localizer, below glide slope
- B.south of localizer, above glide slope✓
- C.north of localizer, above glide slope
- D.south of localizer, below glide slope
Why: Runway QDM 264° (westward). Standing at the runway facing approach (264°), LEFT is to the south, RIGHT is north. 90 Hz on localizer = aircraft in LEFT (yellow) sector = aircraft is south of centreline (left of runway facing west, looking east). 90 Hz on GP = upper lobe = aircraft is above glide slope. Answer: south, above glide slope .