LOW RANGE RADIO ALTIMETER SYSTEM - ADJUSTMENT/TEST
EFFECTIVITY
GJ ALL EXCEPT B-2509, B-2510
1.  Low Range Radio Altimeter System Test
A.  Prepare to Test Low Range Radio Altimeter System
(1)  
Provide electrical power.

(2)  
Check that RADIO ALTM-1 circuit breaker on panel P18 and RADIO ALTM-2 circuit breaker on panel P6 are closed.

(3)  
Allow a 5 minute warm-up period.

B.  Test Low Range Radio Altimeter System
(1)  
At both height indicators check that:

(a)  
Altitude pointer indicates between 0 and -10 feet.

(b)  
Warning flag is out of view.

(2)  
At captain's height indicator, turn the decision height control to the lower mechanical stop, and check that:

(a)  DH light is extinguished.

(3)  
At captain's height indicator, press the self-test switch and check that:

(a)  
DH light is extinguished.

(b)  
Altitude pointer on height indicator indicates 400 +40 feet.

(c)  
Warning flag on height indicator is in view.

NOTE:  Flag is out of view for series II R/T units. Flag is in view for series III R/T units. Series designation is on R/T nameplate.
(4)  
While pressing the test switch in, turn the decision height control on the captain's height indicator until the Captains DH light comes on. Check that:

(a) The DH cursor shall be within + 10 feet of the indicated test altitude.

(5)  
Release test switch on the captain's height indicator and check that:

(a)  
Altitude pointer on height indicator returns to 0 to -10 feet indication.

(b)  
Warning flag on height indicator retracts from view. See Note in step (3) above.

(6)  
Return the Captain's decision height control to the lower mechanical stop. Check that:

(a)  The captain's DH light shall go off.

(7)  
Repeat steps 1.B.(2) thru (6) using first officer's height indicator in place of captain's height indicator.

(8)  
Open the RADIO ALTM-1 circuit breaker. On captain's height indicator, check that:

(a)  
Warning flag comes into view.

(b)  
Altitude pointer shall "freeze".

(9)  
Close the RADIO ALTM-1 circuit breaker. Warning flag goes out of view and altitude pointer returns to 0 to -10 feet indication.

(10)
Repeat (8) and (9) using RADIO ALTM-2 circuit breaker and first officer's height indicator in place of captain's height indicator.

5C8
Oct 20/85 34-48-0 Page 501
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.

LOW RANGE RADIO ALTIMETER ANTENNA - REMOVAL/INSTALLATION
1.  General
A.  The following procedure applies to both transmit and receive antennas.
2.  Remove Antenna (Fig. 401)
A.  Open RADIO ALT-1 and RADIO ALT-2 circuit breaker on load control center panel P6 and P18, as required.
B.  Remove screws securing antenna to airplane structure.
C.  Lower antenna until coaxial connector(s) are accessible.
NOTE:  When lowering antenna, note direction of antenna connector(s) with respect to airplane centerline. This will identify orientation of antenna for installation.
D.  Disconnect coaxial cable(s) from antenna and remove antenna gasket.
3.  Install Antenna (Fig. 401)
A.  Make certain circuit breakers in par. 2 above are opened for LRRA-1 system antennas and LRRA-2 system antennas (if installed).
B.  Check condition of antenna gasket and replace if defective.
NOTE:  Gasket serves the dual function of providing an air pressure seal and conductive path for rf energy.
C.  Check antenna and retaining ring (airplane structure) faying surfaces for corrosion or other foreign material and clean if necessary.
CAUTION:  BE CERTAIN GASKET IS IN GOOD CONDITION AND FAYING SURFACES ARE CLEAN. INADEQUATE RF GROUNDING WILL CAUSE IMPROPER SYSTEM OPERATION.
D.  Apply corrosion preventive material to antenna and retaining ring faying surfaces.
(Ref 51-21-91, Cleaning/Painting)

E.  Place gasket on antenna and align over keying pin (if installed).
F.  Connect coaxial cable(s) to antenna.
G.  Place antenna in mounting recess and align antenna so keying pin (if installed) mates with its positioning hole in retaining ring. If keying pin is not installed, align antenna so connector orientation is in same direction as connectors) on other LRRA antenna(s) (Fig. 401). On some antennas a black mark is painted on the mounting hole in line with the connector.
　
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