T-6A INSTRUMENT NAVIGATION
False glideslope signals may exist in the area of the LOC BC
approach that can cause the glideslope flag alarm to disappear and
present unreliable glideslope information. Disregard all glideslope
signal indications when making a LOC BC approach unless a
glideslope is specified on the approach and landing chart.
The glideslope transmitter is located between 750 feet and 1250 feet from the approach end of
the runway (down the runway) and offset 250 to 650 feet from the runway centerline. It
transmits a vertical glidepath beam of 1.4°. 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.
The glidepath projection angle is normally adjusted to 3° above horizontal so that it intersects the
MM at about 200 feet and the OM at about 1400 feet above the runway elevation. The
glideslope is normally usable to the distance of 10 NM. However, at some locations, the
glideslope has been certified for an extended service volume exceeding 10 NM.
Aircrews must be alert when approaching the glidepath interception. False courses and reverse
sensing will occur at angles considerably greater than the published path. Make every effort to
remain on the indicated glidepath.
Avoid flying below the glidepath to assure obstacle/terrain
clearance is maintained.
When installed with the ILS and specified in the approach procedure, DME may be used:
In lieu of the OM.
As a BC Final Approach Fix (FAF).
To establish other fixes on the LOC course.
In some cases, DME from a separate facility may be used within Terminal Instrument
To provide arc initial approach segments.
As a FAF for BC approaches.
As a substitute for the OM.
1-8 INTRODUCTION TO NAVIGATION SYSTEMS