TM 11-5840-281-35/1
tracks the aircraft from the start of the inbound run,
system
d. Safety Cursor Check. If the alternate cursor in
maintaining the horizontal cross-hair exactly on the
aircraft, while monitoring radar operator radio
Control-Indicators C-6988/TPN-18 is aligned and used
transmissions to the pilot. When the radar operator calls
as a lower safety limit, it must be checked also. To
the aircraft "on glidepath" and the theodolite horizontal
check a lower safety limit cursor, the flight test aircraft
cross-hair is exactly on the aircraft, the theodolite
flies inbound from a point 5 miles from touchdown with
operator calls out "mark" to his assistant. The theodolite
corrections from the radar operator relative to the safety
assistant, who is observing the elevation dial on the
limit cursor instead of the glidepath cursor. The radar
theodolite, records the indicated angle each time the
operator uses the terms "high," "low," and "on lower
theodolite operator says "mark." Upon the completion of
limit." The flight test pilot flies the aircraft at the lower
the run, the indicated angles are averaged to determine
safety limit all the way to the runway. The aircraft must
the actual glidepath angle
clear all terrain obstructions by an altitude equivalent to a
(2) Range mark method. This method uses the
straight line from the end of the runway which is one
range marks to determine the glidepath angle.
degree above a straight line from the end of the runway
Consequently, any error in the range marks will cause a
to the terrain obstruction
e. Range Accuracy Checks. The accuracy of the
corresponding error in the measurement of the glidepath
angle. Before commencing the elevation glidepath
range marks is checked during flight tests by comparing
check, it is necessary to compute the altitude at three
the indicated range of the flight test aircraft, while it is
glidepath intercept points; 6 miles, 3 miles, and 2 miles.
over a fix, landmark, or ground checkpoint, to the known
To compute the glidepath intercept alitudes, multiply the
range of the fix, landmark, or ground checkpoint. Range
intercept range (36,480, 18,240, and 12,160 feet) by the
marks used in the precision scans are common to those
sine of the glidepath angle (refer to the sine of angles
used in the search (surveillance) scans and can be
chart in TM 11-5840-281-12). The flight test aircraft flies
checked in either the surveillance phase or the par
inbound from a point farther than 6 miles from
phase. The 1-mile range marks, however, can be
touchdown and at the altitude computed for the 6-mile
checked more accurately in the par phase, and are most
glidepath intercept. When advised of intercepting the 6-
important to the par functions
f. Coverage. A complete coverage check in the
mile range mark, the pilot immediately descends the
aircraft to the altitude computed for the 3-mile glidepath
precision scans is not applicable to Radar Set AN/TPN-
intercept and continues inbound. When advised of
18 if the coverage has been checked in the surveillance
intercepting the 3-mile range mark, the pilot immediately
phase, since the same antennas and system
descends the aircraft to the altitude computed for the 2-
components are used. The azimuth and elevation limits
mile glidepath intercept. The flight test aircraft continues
of the antenna scans should be checked, however, to
inbound until intercepting the 2-mile range mark. The
determine that optimum coverage is provided for the
radar operator observes the altitude of the aircraft radar
particular operational needs
g. Official Flight Test Evaluation of Radar Operator
return with respect to the glidepath cursor at the three
points of range mark intercept. If the check is an official
Performance. To determine the usability of an overall
flight test, the radar operator also advises the flight test
par facility requires an evaluation of radar operator
pilot of the aircrafts altitude with respect to the glidepath
performance in addition to checks of the system
cursor at each point of range mark intercept
accuracy, alignment, and coverage, since it is difficult to
(3) Other air navigation aids. When other air
determine during the flight test the exact degree to which
navigation aids, such as an instrument landing system
equipment and radar operator contribute to the overall
(ils), also provide a landing service to the same run-way
performance. Erroneous advisaries or instructions and
as Radar Set AN/TPN-18, the glidepath or glidescope
tendencies of radar operators to become confused
information from both systems should be as coincident
during a declared emergency is noted. A series of final
as possible throughout the final approach paths to avoid
approaches is usually made to obtain a user viewpoint.
confusion to the user pilots. If an ils or other service
Attention is paid to the clarity of instructions
exists, compare the systems by monitoring the flight test
aircraft on Control-Indicators C-6988/TPN-18 while the
flight test aircraft is making an approach on the other
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