ILS Approaches

Question 1

Instrument Landing System

Answer 1

● The ILS is a precision final approach.
● It has both horizontal and vertical guidance to the runway.
● The ground equipment for an ILS will consist of the following items:
○ A localizer.
○ A glide path transmitter.
○ An NDB along the approach path.
■ In some locations and approaches, (ILS/DME approach) a DME fix will replace the NDB.

Question 2

ILS Categories

Answer 2

CAT I:
○ This is the “basic” ILS Approach.
○ Operations are permitted down to a minima of 200’ DH and advisory visibility limits are normally ½ SM or RVR 2600’.
○ The actual minima may be higher than 200’ depending on factors like terrain, or whether system components are not installed, or are temporarily unavailable

CAT II:
○ These require special runway, aircraft, and pilot certifications.
○ For exact requirements, see the Manual of All Weather Operations by TC
○ Operations are permitted down to a minima of 100’ DH and an RVR A of 1200’ and RVR B of 600’.
○ CAT II DH is based on Radar Altimeter readings, not barometric readings as are the Category I

CAT III:
○ Require very special runway, aircraft, and pilot certifications.
○ CAT III minima and procedures will be prescribed in the carrier’s operating specifications, in the operator’s operations manual, and CAP.
○ CAT III A (100’ minimum dh, each of RVR A, RVR B and RVR C - not less than 600 feet)
○ CAT III B (50’ minimum, each of RVR A, RVR B and RVR C less than 600 feet but not less than 150 feet)
○ CAT III C - autoland (no DH and no RVR limits).
○ Only Vancouver, Calgary, St. John’s NL and Toronto have CAT III approaches in Canada

Question 3

ILS Identification

Answer 3

● Identification for both the localizer and glide path is transmitted on the localizer frequency in the form of a two-letter or letter-number indicator preceded by the letter “I” (e.g. IOW).
● LOC indicated by “IHV” means the localizer is aligned within 3 degrees of the runway.
● If a localizer is offset by more than this, we will have a designation of “X.” For example, “XHV.”
● When the localizer is used with the glide slope as well as the outer marker (FAF), it is called the “front course.”

Question 4

Localizer

Answer 4

● The localizer operates within the frequency range of 108.1 MHz to 111.95 MHz and provides the pilot with course guidance to the runway centreline left/right.
● The localizer is adjusted to provide an angular width of between 3 ̊ and 6 ̊.
● Normally, the width is 5 ̊, which results in full deflection of the track bar at 2.5 ̊.
● This means that each “dot” or graduation on the Instrument face will be 0.5 ̊ as opposed to 2 ̊ when it is in VOR mode

● The transmitter antenna array is located at the far end of the runway from the approach – typically 1000’ behind the departure end.
● The localizer may be offset up to 3 ̊ from the runway heading; however, the amount of offset will be published as a cautionary note on the approach plate
● If there is a “back course,” then these parameters will stand for both the front course and the back course, except glide path information should be ignored

Question 5

Glide slope

Answer 5

● Provides vertical guidance.
● The glide path transmitter operates within the frequency range of 329.3 to 335.0 MHz.
● This frequency is paired with the associated localizer frequency
● There is no useable back course.
● The antenna array is located approximately 1000’ from the approach end of the runway and offset approximately 400’ from the runway centreline.
● The optimum threshold crossing height of the Glide Slope is 50’.
● The maximum height is 60’
● At some of the larger airports, an ILS is installed at each end of a runway.