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Sunday 12th October 2008
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Brainteasers Interactive Quiz #37:
ILS Components

When the ceiling is low and the visibility is poor and the wind is howling, pilots need all the help they can get in order to navigate to the runway and make a successful landing. The most common precision instrument approach is the ILS (Instrument Landing System), and instrument students spend many hours practicing and honing their skills at flying a stable and accurate ILS approach. Keeping the needles centered is a pilot's first priority, but it's also important to have a good working knowledge of the entire ILS system, and how each of its components contributes to the pilot's positional awareness. Irv Siegel's latest quiz will test your knowledge of those components and the tolerances involved in the design and execution of an ILS approach.

by Irv Siegel

NOTE: This quiz is based on information found in the Aeronautical Information Manual (AIM) and FAA Handbook 8260.3 "Terminal Instrument Procedures (TERPS)."

1. The localizer provides course guidance throughout the descent path to the
a. 5 NM
b. 10 NM
c. 18 NM
d. 25 NM
e. 33 NM
many miles from the antenna?


runway threshold to 10 degrees either side of the course along a radius of how
2. The localizer provides course guidance throughout the descent path to the
a. 5 NM
b. 10 NM
c. 18 NM
d. 25 NM
e. 33 NM
many miles from the antenna?


runway threshold to 35 degrees either side of the course along a radius of how
3. What is the width of the localizer (full-scale fly-left to full-scale
a. 700'
b. 800'
c. 900'
d. 1,000'
fly-right) at the runway threshold?

4. The term "glide path" means that portion of the glide slope that
a. 1.2 degrees
b. 1.4 degrees
c. 2.8 degrees
d. 3.0 degrees
e. 3.5 degrees
intersects the localizer. What is the vertical width of the glide path beam?

5. Select the correct statement concerning the threshold crossing height (TCH):
a. The published TCH represents the height of the actual glide path on-course
b. The TCH is used as a reference for planning purposes which represents the
be, if that aircraft remains on a trajectory formed by the four-mile-to-middle
c. Pilots must be aware of the vertical height between the aircraft's glide
comfortable wheel crossing height is approximately 10 to 15 feet, depending on
height above the runway threshold that an aircraft's glide slope antenna should
indication above the runway threshold.


marker glidepath segment.


slope antenna and the main gear in the landing configuration. Tests indicate a
the type of aircraft.

6. When installed with the ILS and specified in the approach procedure, DME
a. in lieu of the outer marker (OM).
b. as a back course (BC) final approach fix (FAF).
c. to establish other fixes on the localizer course.
d. all of the above
e. a and b only
f. a and c only
g. b and c only
may be used

7. In some cases DME from a separate facility may be used within terminal
a. to provide arc initial approach segments.
b. as a final approach fix (FAF) for back course (BC) approaches.
c. as a substitute for the outer marker (OM).
d. all of the above
e. a and b only
f. a and c only
g. b and c only
instrument procedures (TERPS) limitations

8. The middle marker (MM) indicates a position where an aircraft on the glide
a. 2,000 feet
b. 2,500 feet
c. 3,000 feet
d. 3,500 feet
distance from the MM to the landing threshold?


path will be at an altitude of approximately 200' above the elevation of the
touchdown zone (TDZ). For the typical ILS approach, what is the approximate
9. Compass locator transmitters are often situated at the MM and OM sites.
The transmitters have a power of less than 25 watts and operate between 190 and
535 kHz. These transmitters have a range of at least


a. 15 miles.
b. 20 miles.
c. 25 miles.
d. 30 miles.
10. At some locations, higher-powered radio beacons are used as OM compass
a. 100 watts.
b. 200 watts.
c. 300 watts.
d. 400 watts.
information. These higher-powered radio beacons may have output power as high as


locators. These generally carry Transcribed Weather Broadcast (TWEB)
11. Bonus question: The ATIS for your arrival airport states that the glide
a. clearly a mistake on the controller's part. ATC should not clear you for
an ILS approach if the glide slope is out of service.


b. an indication that the glide slope is back in service, and you must report
c. normal procedure. When the glide slope fails, the ILS reverts to a
nonprecision localizer approach.


shows non-precision localizer approach minimums. The approach controller clears
slope for the only ILS approach at that airport is out of service, and indeed
the failure of your glide slope receiver.


you for that ILS approach. This is