BY ORDER OF THE SECRETARY OF THE AIR FORCE AIR FORCE ...

80
AFMAN 11-217V1 3 JANUARY 2005
identification is being received. Pilots should use extreme caution and
maintain good situational awareness while flying an ILS or localizer approach
in actual weather conditions.
5.2.2.2.4. Marker Beacon. The marker beacon light and aural tone indicate
proximity to a 75-MHz marker beacon transmitter; for example, ILS outer marker
(OM), middle marker (MM), inner marker (IM), etc. As the aircraft flies through
the marker beacon signal pattern, the light flashes and the aural tone sounds in
Morse code indicating the type of beacon. The marker beacon light functions
independently of ILS/VOR/TACAN signals.
5.2.3. Range Indicator. Range indicators display slant range distance in nautical miles to
a DME transponder. For practical purposes, you may consider this a horizontal distance
except when the aircraft is very close to the station. DME range information is subject to
line-of-sight restrictions and altitude directly affects the reception range.
Figure 5.8. Bearing Distance Heading Indicator (BDHI).
5.2.4. Bearing-Distance-Heading Indicator (BDHI) (Figure 5.8).
5.2.4.1. BDHI Display. The BDHI displays aircraft heading with navigational
bearing data and range information. Except for the range indicator, the BDHI is
similar in appearance and function to the RMI previously described.
5.2.4.2. BDHI Components. The BDHI consists of a rotating compass card, two
bearing pointers, a range indicator, and a range warning flag. Some BDHIs also have
a heading marker, a heading set knob, and a power warning flag.
5.2.4.3. Compass Card Actuation. The compass card is actuated by the aircraft
compass system, which normally includes pilot-operated controls that permit the
BDHI compass card to operate in a slaved or non-slaved direct gyro (DG) mode. In
the slaved mode, the aircraft magnetic heading is displayed beneath the top index or
lubber line. In the nonslaved DG mode, the compass card serves as a heading
reference after being corrected to a known heading. The card is manually corrected
for the DG mode by a switch on the compass control panel.
5.2.4.4. Heading Marker. The heading marker, if incorporated, may be positioned on
the compass card by use of the heading set knob. Once positioned, the marker