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military aircraft. This capability is provided by an airborne cryptographic computer which generates
coded replies in response to valid interrogations generated by an interrogator cryptographic computer.
The aircrew or maintenance personnel set codes by a keying device prior to flight.
5.17.3.8. Mode 4, Enable Switch. Controls operation of Mode 4 and has three positions which permits
aural and reply lamp monitoring of valid Mode 4 interrogations and replies in AUDIO: (1) OUT—No
monitoring capability, (2) LIGHT—Reply lamp monitoring only, and (3) REPLY LAMP—Used with
Mode 4 only.
5.18. Identification Friend or Foe (IFF) and Selective Identification Feature (SIF). IFF is an
airborne transponder that transmits coded signals when interrogated by ground-based search radar which
was first used during World War II. Pulses received from the airborne equipment produce blips on the
ground-based radarscope and are used to positively identify and locate aircraft. The addition of an SIF
allows faster isolation and identification of any aircraft under surveillance. The ground controller can
establish and maintain positive identification when a designated SIF mode and code is set into the
airborne transponder. Initial identification is usually established by using the IP or indent function of the
airborne set. Tracking is maintained by setting the requested mode and code into the aircraft equipment.
168 AFPAM11-216 1 MARCH 2001
Chapter 6
MAP READING
Section 6A— Introduction
6.1. Basics. Map reading is the determination of aircraft position by matching natural or built-up
features with their corresponding symbols on a chart. It is one of the more basic aids to dead reckoning
(DR) and certainly the earliest used form of aerospace navigation. The degree of success in map reading
depends upon a navigator's proficiency in chart interpretation, ability to estimate distance, and the
availability of landmarks.
Figure 6.1. Landmarks as Checkpoints, Populated Areas.
6.2. Checkpoints. Checkpoints are landmarks or geographic coordinates used to fix the position of the
aircraft. By comparing the aircraft position to that of the checkpoint, the navigator fixes the aircraft's
location. Arrival over checkpoints at planned times is a confirmation of the wind prediction and
indicates reliability of the predicted track and groundspeed. If the aircraft passes near but not over a
checkpoint, the anticipated track was not made good. If checkpoints are crossed but not at the predicted
time, the anticipated GS was in error. Prudent navigators are quick to observe and evaluate the
difference between an anticipated position and an actual position. They must make corrections to
maintain their intended course as soon as possible because small errors can be cumulative and may
eventually result in the aircrew becoming lost. It is also important to closely monitor time control. On
many map reading missions, the aircraft is required to pass over certain checkpoints at exact times. On
these missions, navigators must adjust the airspeed to make good their anticipated GS.
AFPAM11-216 1 MARCH 2001 169
6.2.1. Before fixing each position, navigators should look for several related details around each
checkpoint to make sure it has been positively identified. For example, if the checkpoint is a small town,
there may be a lake to the north, a road intersection to the south, and a bridge to the east.
6.2.2. Generally, it is better to select a feature on the chart and then seek it on the ground rather than to
work from the ground to the chart. The chart does not show all the detail which is on the ground, and
one could easily become confused. Checkpoints should be features or groups of features that stand out
from the background and are easily identifiable. In open areas, any town or road intersection can be
used; however, these same features in densely populated areas are difficult to distinguish. Figures 6.1
and 6.2 compare various chart and corresponding photo areas and list the features to look for when
identifying landmarks as checkpoints.
Figure 6.2. Landmarks as Checkpoints, Coastal Areas.
6.3. Chart Selection. Use a chart for map reading that provides sufficient natural and built-up features
to accurately position the aircraft. The Operational Navigation Chart (ONC), with a scale of
1:1,000,000, has excellent cultural and relief portrayal. For increased detail, a Tactical Pilotage Chart
(TPC), with a scale of 1:500,000, or a Joint Operations Graphics (JOG) Chart with a scale of 1:250,000,
may be used. To extract minute details or precise coordinates, use a topographic line map (TLM) series
chart, typically at a scale of 1:50,000.
Section 6B— Map Reading Procedures
6.4. Basics. When inflight, orient the chart so that north on the chart is toward true north (TN). The
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