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

(c)  
Warning flag on height indicator retracts from view.

(4)  
Repeat steps (2) and (3) for F/O's height indicator using F/O's height indicator and ADI.

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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.

(5)  At captain's height indicator, depress self-test button, then slowly adjust DH cursor to increasing altitude setting and check that:
(a)  Captain's DH lights illuminate when DH cursor setting is within 士5 feet of displayed test altitude.
NOTE:  The panel-mounted DH light will decrease in intensity approximately 1/2 second after it comes on.
(6)  
Release self-test button and check that captain's DH lights remain illuminated.

(7)  
Adjust master dim control and check that intensity of ADI-mounted DH light is controlled.

(8)  
At captain's height indicator, set DH cursor to between -15 and -20 feet and check that captain's DH lights go out.

(9)  
Repeat steps 1.B.(5) thru (8) using first officer's DH lights and height indicator in place of captain's.

(10)
Pull RADIO ALTM-1 circuit breaker and check warning flag on captain's height indicator comes into view.

(11)
Pull RADIO ALTM-2 circuit breaker and check warning flag on F/O's height indicator comes into view.

(12)
Close circuit breakers and check warning flags on height indicators retract from view and height indicators indicate between 0 and -10 feet.

NOTE:  Radio altimeter zero height indication normally is set to read zero at touchdown of landing gear wheels. When airplane is at rest on ground, altitude indication on height indicators will vary according to airplane loading, system tolerance, and difference in zero setting of each LRRA system to compensate for antenna height difference above ground at touchdown.

(13)
Remove electrical power, if required.

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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.
CAUTION:  BE CERTAIN ANTENNAS ARE PROPERLY ALIGNED. SIGNAL COUPLING BETWEEN IMPROPERLY ALIGNED ANTENNAS WILL CAUSE SYSTEM OPERATIONAL PROBLEMS.
H.  Install screws securing antenna to airplane structure.
NOTE:  Small voids between antenna and airplane structure may be filled with aerodynamic sealer.
I.  Check dc resistance between antenna base and airplane skin metal. Resistance should not exceed 0.10 ohm.
J.  Perform operational check of system (Ref 34-48-0, Adjustment/Test).
5D6 Oct 20/85 34-48-11 Page 401 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
　
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