Section III. OPERATION UNDER UNUSUAL CONDITIONS

TM 11-5826-258-24

cated about 1 mile from the edge of the runway. Pass-

(7) After proper elapsed time, fly a 45 left turn

age of the aircraft over the middle marker is identified

by the compass. After 45 seconds, make a 180 right

aurally by alternate dots and dashes and visually by

turn by compass.

the amber marker lamp in the cockpit (or single lamp

(8) Fly to complete the procedure until the final

as applicable).

approach course is intercepted and the VOR/localizer

(4) The inner marker beacon transmitter is gen-

needle is centered. The needle deviates in the direction

erally located at the edge of the runway. Passage over

of the proper path when inbound.

the inner marker is identified aurally by a series of

(9) Fly in the direction which the VOR/localizer

dots and visually by the white marker lamp in the

and glideslope needles deviate. When both needles are

cockpit (or single lamp as applicable).

centered, the aircraft is on the correct glidepath and

(5) Marker beacon receiver sensitivity is con-

localizer path.

trolled in the aircraft by the receiver control panel MB

b. Marker Beacon Operation.

SENS HI-LO control. High sensitivity operation is usu-

(1) For a ground facility to supply the pilot with

ally used when making an approach to the outer mark-

distance data relative to the beginning of the runway,

er beacon or while enroute. Low sensitivity operation

three marker beacon transmitters are generally pro-

may be employed for positive identification of marker

vided along the approach path to the runway.

beacon passage.

(2) The outer marker beacon transmitter is usual-

(6) The volume of the marker beacon audio signals

ly located from 4 to 7 miles from the runway. Passage

is controlled by the receiver control MB VOL knob.

of the aircraft over the outer marker is aurally iden-

tified by a series of keyed dashes and visually by a blue

2-7. Stopping Procedure

marker lamp in the cockpit (or single lamp as appli-

Stop the receiving set by turning the NAV VOL con-

cable).

trol to OFF.

(3) The middle marker beacon transmitter is lo-

Section III. OPERATION UNDER UNUSUAL CONDITIONS

2-8. Warning Flags

section of the receiver.

c. Receiver Section Malfunction. The three receiver

a. VOR/LOC Warning Flag. A red LOC flag appears

sections (VOR/LOC-GS-MB) perform independently of

on the course indicator whenever the selected VOR or

each other. Performance degradation within any one

localizer signal is unreliably weak or a malfunction oc-

of the major sections will not affect the performance

curs in the VOR/LOC section of the receiver. (The

of the others,

course indicator is not part of Radio Receiving Set

AN/ARN-123.)

2-9. Extreme Temperatures

b. GS Warning Flag. A red GS flag appears on the

course indicator whenever the glideslope signal is un-

The receiving set may take a little longer to warm up

reliably weak or a malfunction occurs in the glideslope

(up to 3 minutes) under conditions of extreme cold.

Section IV. PREFLIGHT (DAILY) OPERATIONAL CHECK

2 - 1 0 . General

generated by a ground station, or ramp test

Set.

The operational check given in paragraph 2-11 supple-

a. Set the course indicator OBS control for a 315

ments the inspection procedures in the aircraft opera-

indication under the course index.

tor's condensed checklist. The operational check

b. Move the control unit VOR/MB switch to the

should be performed just before flight. The pilot or co-

TEST position (down).

pilot should report any malfunction or failure noted in

c. The CDI deviation needle should indicate center

flight.

2 dots.

d. The VOR/LOC flag should be buried,

2-11. Operational Check/Self-Test

e. The RMI should point to the 315 radial (5).

NOTE

f. The marker beacon lamp(s) should illuminate.

This test requires an external VOR rf signal

2-5