Section IV. FLIGHT LINE TESTS

TM 11-5826-257-24

the airframe, and remove the mount.

4-10. Removal and Replacement of Mount

b. Replacement.

a. Removal.

(1) The receiver mount is installed in the

(1) Remove the receiver as described para-

reverse order of removal (para 49b).

graph 4-9a.

(2) Tighten the vibration isolator mounting

(2) Remove the four screws that attach each

screws.

of the vibration isolators and the ground straps to

Section IV. FLIGHT LINE TESTS

( 5 ) Set AUDIO SELECTOR switch to

4 - 1 1 . General

GLIDESLOPE.

a. The operational tests given in paragraphs 4

(6) Set NAV GS switch to GS.

12 and 413 are performed on the flight line with

(7) Set MICROVOLTS control to 1K micro-

the equipment installed in the aircraft. These

volt.

tests should be performed before removal and

replacement of components as a result of inflight

(8) Set METER switch to CAR.

problems or malfunctions observed during opera-

(9) Adjust CARRIER SET control for redline

tional checks and should be performed as part of

indication on meter.

the aircraft intermediate preventive maintenance

(10) Set LOC-GS switch to DOWN.

checks and services. Components found to be

(11) Position the SG-13/ARN 50 feet directly

malfunctioning should be removed for bench test-

in front of the aircraft center and move towards

ing in accordance with paragraphs 4-16 and 417.

the aircraft until the glideslope warning flag is

b. The glideslope tests are made using Signal

driven out of view.

Generator SG-13/ARN; and the marker tests are

b. Glideslope Test Procedure.

made using Test Oscillator BC-376. The aircraft

(1) Set MICROVOLTS control to 10K micro-

and receiver power must be on.

volt.

NOTE

(2) Set LOC-GS control to center (white line).

If the aircraft engines are operated dur-

(3) Check to see that the glideslope deviation

ing the following tests, the pilot or an

indicator in the aircraft is within the center

authorized crewmember will start and

donut.

operate the engines. If the aircraft en-

(4) Set LOC-GS control to UP.

gines are not operated, use an auxiliary

(5) Check to see that glideslope deviation

power source to prevent excessive drain

indicator in the aircraft deflects fullscale upward.

on the aircraft battery. Refer to the air-

(6) Set LOC-GS control to DOWN.

craft manuals for connection and power

requirements, and for setting of commu-

(7) The glideslope deviation indicator in the

nication power controls.

aircraft shall deflect fullscale downward.

c. The tests should be conducted at a location

which is free of electromagnetic energy reflecting

4-13. Flight Line Marker Beacon Operational

surfaces such as buildings, other aircraft, etc.

Tests

Flight line tests of the marker beacon receiver

4-12. Flight Line Glideslope Operational Tests

are performed using Test Oscillator BC-376. The

a. Test Setup.

BC-376, with its antenna fully extended, must be

(1) With the SET LINE TO 21V control OFF,

placed 10 to 20 feet from the marker beacon

connect the SG13/ARN to a 21- to 29-volt dc

receiver antenna. A headset can be used to moni-

portable power source.

tor the marker beacon audio output.

(2) Set METER switch to LINE.

a. Turn on the BC-376 and move it toward the

(3) Rotate SET LINE TO 21V control for 21

receiver antenna until a strong signal is heard in

volts 0.5 on meter.

the headset.

(4) Set the MEGACYCLES control to 109.30

b. Set the BC-376 MODULATION switch to

(332.00 MHz), and set receiver frequency (in air-

400. The OUTER marker lamp on the aircraft

craft) to 109.30, or any frequency with a reported

instrument panel must light, and the MIDDLE

discrepancy.

and AIRWAY lamps must not light.

4-3