ILS, Radio Altimeter & Landing Aids

C. self-contained on-board aid used to measure the true height of the aircraft

A radio altimeter is a self-contained on-board aid that measures true height above the terrain.

A. Height above terrain

A radio altimeter gives true height above the terrain directly below the aircraft, not altitude.

C. 0 to 2500ft

A low-range radio altimeter measures true height above the terrain from 0 to about 2,500 ft.

A. Frequency modulated carrier wave.

A radio altimeter transmits a frequency-modulated carrier and measures the frequency difference of the echo.

C. SHF

Radio altimeters operate in the SHF band (about 4.3 GHz).

A. 7 cm

A radio altimeter works near 4.3 GHz (SHF): wavelength = 300 / 4300 = about 7 cm.

A. 400 Hz; dashes

Outer marker 400 Hz, continuous dashes, blue light; middle 1300 Hz dot-dash, amber; inner 3000 Hz dots, white. All on 75 MHz.

The question was recalled without its options; these options were written to it.

C. radio conversations

A CVR records voice communications by radio and interphone and the flight-deck sounds; it does not record cabin-crew intercom or PA announcements that were not selected on the flight deck.

A. magenta

Magenta is used for the ILS deviation pointer, active route and selected heading; cyan for selected/sky items; amber for cautions.

The question was recalled without its options; these options were written to it.

A. Magenta

On an EFIS display the selected heading and the ILS deviation are magenta.

A. 660 ft

The bar shows where the glide path is: below centre means the aircraft is above it by 2 x 0.14 = 0.28 deg. Height = 1.9 x 6076 x tan(3.28) = 660 ft (on the path it would be about 605 ft).

C. Height of the main wheel above the ground.

In the landing configuration the radio altimeter is calibrated to indicate the height of the main wheels above the ground.

B. up and left

150 Hz dominates to the right of the localiser and below the glide path; so fly left and up. (More 90 Hz: fly right and down.)

The question was recalled without its options; these options were written to it.

B. the radio altimeter

CAT II/III minima are true heights above the touchdown zone, so the DH is set and read on the radio altimeter. CAT I normally uses a barometric decision altitude.

C. 1 km, 1300 Hz, amber

The middle marker is about 1 km out, 1300 Hz, amber.

B. frequency modulated waves, where the difference between the transmitted wave and the received wave is measured

A modern radio altimeter transmits a frequency-modulated (FMCW) signal and measures the frequency difference between the transmitted and returned waves to get height.

B. 1236 ft in the landing attitude

Typical radio altimeter accuracy is about +/- 3 % (+/- 5 ft): 1280 - 38 - 5 = 1236 ft. It is calibrated (installation delay) to be correct in the landing attitude.

The question was recalled without its options; these options were written to it.

A. 6°

The first false glide path appears at about twice the true glide angle, so 6 deg for a 3 deg glide path (the usable path lies between 0.45 and 1.75 times the glide angle).

B. red over white (far bar red, near bar white)

Near (lower) bar white and far (upper) bar red = on slope. Both white = too high; both red = too low. (On a 3-bar VASI, long-bodied aircraft use the middle and far bars.)

Our independent check could not confirm this answer from the official sources we hold; treat it with care and confirm with your instructor.

C. 1.35 deg (0.45 theta) to 5.25 deg (1.75 theta)

ICAO glide path coverage: from 0.45 theta to 1.75 theta above the horizontal: 0.45 x 3 = 1.35 deg, 1.75 x 3 = 5.25 deg.

The question was recalled without its options; these options were written to it.

A. 1550 ft

The correct answer is: 1550 ft.

A. Fly right and fly down

More 90 Hz: the aircraft is to the left of the localiser (fly right) and above the glide path (fly down).

A. UHF

Glide path 329.15-335 MHz (UHF), paired automatically with the VHF localiser (108.10-111.95 MHz).

The question was recalled without its options; these options were written to it.

A. 550 m

CAT I: DH not below 200 ft with visibility 800 m or RVR not less than 550 m.

The question was recalled without its options; these options were written to it.

B. the height indication is removed and a failure flag appears

A detected system failure removes the reading and shows a warning flag (with an alert), so the crew never uses a false height near the ground.

C. multiple lobes of radiation patterns

False glide paths arise from the multiple lobes in the glide path antenna radiation pattern.

B. 4200 MHz to 4400 MHz

Low-range radio altimeters use 4200-4400 MHz.

A. 150 m

ICAO Annex 14: touchdown zone markings are pairs of rectangular marks spaced 150 m apart, starting 150 m from the threshold.

The question was recalled without its options; these options were written to it.

C. 1.96 NM

Distance = 670 / tan 3.2 deg = 11,970 ft = 1.97 NM.

B. 5.29 deg

The angle is set by height and ground distance only: 18,000 ft over 32 x 6076 = 194,400 ft: tan = 0.0926, angle 5.29 deg. The wind changes the TAS needed, not the angle.

The question was recalled without its options; these options were written to it.

A. increase by about 85 ft/min

Less headwind = 17 kt more groundspeed. ROD for 3 deg is about 5 x GS, so it must increase by about 5 x 17 = 85 ft/min.

The question was recalled without its options; these options were written to it.

C. only permitted with certain precautions, to safeguard the health of personnel and to protect equipment

Airborne weather radar may be operated on the ground only with precautions to protect people (radiation hazard) and equipment.

B. 7.8 nm

Distance = height / tan 3 deg = 2500 / 0.0524 = 47,700 ft = 7.85 NM.

A. 8.3Nm

A 3 deg glide path descends about 300 ft per NM, so 2,500 / 300 = 8.3 NM. Exact trigonometry gives 2,500 / tan 3 = 7.9 NM; 8.3 NM is the expected answer among the options offered.

B. Loss of true height data

A radio altimeter supplies true height above the terrain; if it fails, that height data is lost.

C. 112.20 MHz

Between 108 and 112 MHz, localisers use ODD tenths (108.10, 109.90, 111.95) and VORs EVEN tenths; above 112 MHz everything is VOR.

C. 0 to 2500 ft

A radio altimeter reads true height from 0 to about 2,500 ft.

A. 109.15MHz

ILS localiser frequencies are 108.10-111.95 MHz with an odd tenth (109.15).

A. +/- 10 deg to 25 NM and +/- 35 deg to 17 NM

Localiser: 25 NM within 10 deg of the centreline, 17 NM between 10 and 35 deg.

The question was recalled without its options; these options were written to it.

B. south of the localiser, above the glide path

90 Hz dominant = left of the localiser (looking along the approach) and above the glide path. Approaching on 264 (westwards), left is south.

The question was recalled without its options; these options were written to it.

A. +/- 8 deg out to 10 NM

Glide path: 8 deg either side of the localiser centreline to 10 NM.

The question was recalled without its options; these options were written to it.

B. 2.5 dots fly up

Below 2.5 dots fly-up obstacle clearance is no longer guaranteed by the glide path coverage.

Our independent check found that more than one option can be argued for, as worded in the recall. The key gives the answer most references support.

The question was recalled without its options; these options were written to it.

A. 600 ft/min

Rule of thumb for 3 deg: ROD = GS x 5 = 600 ft/min (exactly 120 x 101 x tan 3 = 637).

The question was recalled without its options; these options were written to it.

C. decision height equal to at least 200 ft

A Category I precision approach has a decision height of not less than 200 ft.

A. 2.5 deg or more

The localiser is much more sensitive than a VOR: full scale is about 2.5 deg (course width about 5 deg), so a pinned needle means 2.5 deg or more.

The question was recalled without its options; these options were written to it.

B. the received signal is absent or too weak (or the receiver fails)

The flag monitors signal strength and receiver health, not position: deviation is shown by the needle, loss of a usable signal by the flag.

A. 0.7 deg above or below the glide path

The glide path indicator is very sensitive: full scale about 0.7 deg (0.14 deg per dot on a 5-dot scale).

B. lower than 100 ft, or no decision height

CAT I: DH not below 200 ft. CAT II: 100-200 ft. CAT IIIA: below 100 ft or none, with an RVR minimum of a few hundred metres.