INSTRUMENT LANDING SYSTEM (ILS) BASICS
You will be introduced to the ILS approach in the T-39 syllabus. The following is
information taken from the Aeronautical Information Manual (AIM) and the T-39 NATOPS to
assist you in preparation for ILS approaches. The T-39 and most other aircraft have ILS. You
will be expected to know the basics of the ILS/Localizer system.
The ILS is a precision approach similar to the PAR, with the exception of a final
controller using radar to verbalize azimuth and glideslope information, this information is
displayed on the aircraft flight instruments for you to interpret. An ILS consists of two
components, the localizer and the glideslope. The localizer provides the azimuth (centerline)
portion of the ILS. Glideslope must be available, otherwise an approach must revert to the
localizer minimums (higher than an ILS). The glideslope is normally 3º but can be higher
depending on local terrain (Refer to minimums section in the front portion of the approach
plates). Corresponding VSI/VVI information for a given glideslope at a given airspeed can
be found on the inside back cover of any approach plate.
2. ILS Minimums
There are three categories of ILS minimums, but the T-39G is only qualified for
Category-I minimums. For general knowledge, the three categories are:
Category I - 200 - 1/2 (2400RVR)
Category II - 100 - 1/4 (1200RVR)
Category III - 0 - 0
3. ILS/Localizer Transmitter
Your Approach plate will specify the ILS frequency (see any ILS approach plate). It will
be contained in a box that has an 'I' preceding the airfield's 3 letter identifier (such as: I-PNS
or I-MOB). If the box has a TACAN channel, the ILS provides DME (see Mobile Regional).
If the ILS does not have DME and a TACAN is co-located on the field (see Gulfport), then
you will have to select the TACAN channel and the ILS frequency. TACAN DME is
displayed on the EHSI and DME associated with the VHF NAV (VOR/LOC) frequency (if
available) is displayed on the digital DME gauge.
4. Marker Beacons (Fan Markers)
Marker Beacons are available with some ILS/Localizer systems. Ordinarily there are two
Marker Beacons associated with an ILS: the Outer Marker (OM) and the Middle Marker
(MM). The Outer Marker always transmits at 400 Hz, and is indicated by an aural signal and