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6/17/21 

AIM 

course and runway. Circling minimums only are 
published where this alignment exceeds 30 degrees. 

3. 

A very limited number of LDA approaches 

also incorporate a glideslope. These are annotated in 
the plan view of the instrument approach chart with 
a note, “LDA/Glideslope.” These procedures fall 
under a newly defined category of approaches called 
Approach with Vertical Guidance (APV) described in 
paragraph 5

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5, Instrument Approach Procedure 

Charts, subparagraph a7(b), Approach with Vertical 
Guidance (APV). LDA minima for with and without 
glideslope is provided and annotated on the minima 
lines of the approach chart as S

LDA/GS and 

S

LDA. Because the final approach course is not 

aligned with the runway centerline, additional 
maneuvering will be required compared to an ILS 
approach. 

d.  Glide Slope/Glide Path 

1. 

The UHF glide slope transmitter, operating 

on one of the 40 ILS channels within the frequency 
range 329.15 MHz, to 335.00 MHz radiates its signals 
in the direction of the localizer front course. The term 
“glide path” means that portion of the glide slope that 
intersects the localizer. 

CAUTION

 

False glide slope signals may exist in the area of the 
localizer back course approach which can cause the glide 
slope flag alarm to disappear and present unreliable glide 
slope information. Disregard all glide slope signal 
indications when making a localizer back course 
approach unless a glide slope is specified on the approach 
and landing chart. 

2. 

The glide slope transmitter is located between 

750 feet and 1,250 feet from the approach end of the 
runway (down the runway) and offset 250 to 650 feet 
from the runway centerline. It transmits a glide path 
beam 1.4 degrees wide (vertically). The signal 
provides descent information for navigation down to 
the lowest authorized decision height (DH) specified 
in the approved ILS approach procedure. The 
glidepath may not be suitable for navigation below 
the lowest authorized DH and any reference to 
glidepath indications below that height must be 
supplemented by visual reference to the runway 
environment. Glidepaths with no published DH are 
usable to runway threshold. 

3. 

The glide path projection angle is normally 

adjusted to 3 degrees above horizontal so that it 

intersects the MM at about 200 feet and the OM at 
about 1,400 feet above the runway elevation. The 
glide slope is normally usable to the distance of 
10 NM. However, at some locations, the glide slope 
has been certified for an extended service volume 
which exceeds 10 NM. 

4. 

Pilots must be alert when approaching the 

glidepath interception. False courses and reverse 
sensing will occur at angles considerably greater than 
the published path. 

5. 

Make every effort to remain on the indicated 

glide path. 

CAUTION

 

Avoid flying below the glide path to assure 
obstacle/terrain clearance is maintained. 

6. 

The published glide slope threshold crossing 

height (TCH) DOES NOT represent the height of the 
actual glide path on

course indication above the 

runway threshold. It is used as a reference for 
planning purposes which represents the height above 
the runway threshold that an aircraft’s glide slope 
antenna should be, if that aircraft remains on a 
trajectory formed by the four

mile

to

middle 

marker glidepath segment. 

7. 

Pilots must be aware of the vertical height 

between the aircraft’s glide slope antenna and the 
main gear in the landing configuration and, at the DH, 
plan to adjust the descent angle accordingly if the 
published TCH indicates the wheel crossing height 
over the runway threshold may not be satisfactory. 
Tests indicate a comfortable wheel crossing height is 
approximately 20 to 30 feet, depending on the type of 
aircraft. 

NOTE

 

The TCH for a runway is established based on several 
factors including the largest aircraft category that 
normally uses the runway, how airport layout affects the 
glide slope antenna placement, and terrain. A higher than 
optimum TCH, with the same glide path angle, may cause 
the aircraft to touch down further from the threshold if the 
trajectory of the approach is maintained until the flare. 
Pilots should consider the effect of a high TCH on the 
runway available for stopping the aircraft. 

e.  Distance Measuring Equipment (DME) 

1. 

When installed with the ILS and specified in 

the approach procedure, DME may be used: 

(a) 

In lieu of the OM; 

Navigation Aids 

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