(3)
LRRA receive antenna, M1739 (No. 1) or M1740 (No. 2).

(4)
Wiring.

C. Circuit Breakers
(1) These are the primary circuit breakers related to the fault:
CAPT Electrical System Panel, P18-1
Row Col Number Name
B 4 C01384 RADIO NAVIGATION RADIO ALTM 1

F/O Electrical System Panel, P6-1
Row Col Number Name
A 16 C01385 RADIO NAVIGATION RADIO ALTM 2

D. Related Data
(1)
(SSM 34-33-11).

(2)
(SSM 34-33-21).

(3)
(WDM 34-33-11).

(4)
(WDM 34-33-21).

E. Initial Evaluation
(1) Do
this
task:
Low
Range
Radio
Altimeter
(LRRA)
BITE
Procedure,
34-33
TASK
801.

EFFECTIVITY

34-33 TASKS 804-805
SIL ALL
Page 211 D633A103-SIL Feb 15/2010

(a)  
If the radio altimeter display and the RA flag do not show on the captain’s or F/O’s displays, then do the Fault Isolation Procedure below.

(b)  
If the radio altimeter display shows on the captain’s or F/O’s displays, then there was an intermittent fault.

F. Fault Isolation Procedure
(1)  Use a time domain reflectometer (TDR) test set time domain reflectometer, COM-5187to do an electrical check of the coaxial cable and antenna:
(a)  
Remove the LRRA receiver/transmitter. To remove it, do this task: Low Range Radio Altimeter (LRRA) Receiver/Transmitter (R/T) Removal, AMM TASK 34-33-21-000-801.

(b)  
Connect the TDR test set time domain reflectometer, COM-5187at pins 71 and C71 of the applicable connector at the LRRA receiver/transmitter (WDM 34-33-11, WDM 34-33-21).

LRRA
TDR  CONNECTOR

LRRA-1 (M1735) TEST SET  D3667B
XMTR ANTENNA
TDR --------------------pin71 TDR --------------------pinC71

LRRA-1 (M1735) TEST SET D3667A
RCVR ANTENNA

TDR --------------------pin71 TDR --------------------pinC71

LRRA-2 (M1736) TEST SET D3669
XMTR ANTENNA

TDR --------------------pin71 TDR --------------------pinC71

LRRA-2 (M1736) TEST SET D3669A
RCVR ANTENNA

TDR --------------------pin71 TDR --------------------pinC71

(c)  
Do an electrical check of the coaxial cable and the antenna.

NOTE: The TDR test set has instructions which tell how to do the check of the cable and antenna.

(d)  
Disconnect the TDR test settime domain reflectometer, COM-5187.

(e)  
Re-install the LRRA receiver/transceiver. To install it, do this task: Low Range Radio Altimeter (LRRA) Receiver/Transmitter (R/T) Installation, AMM TASK 34-33-21-400-801.

(f)  
If you find a problem with the coaxial cable, then do these steps: 1) Replace the coaxial cable (WDM 34-31-11). 2) Do
this
task:
Low
Range
Radio
Altimeter
(LRRA)
BITE
Procedure,
34-33
TASK
801.
3) If the radio altimeter display shows on the captain’s or F/O’s displays, then you

corrected the fault.
(g)  If you find a problem with the antenna, then do these steps:
1) Replace the LRRA antenna.
These are the tasks:

EFFECTIVITY SIL ALL  34-33 TASK 805 
D633A103-SIL BOEING PROPRIETARY -Copyright # Unpublished Work -See title page for details  Page 212 Feb 15/2010 

Low Range Radio Altimeter (LRRA) Antenna Installation, AMM TASK 34-33-11-400-801.
2)  Do
this
task:
Low
Range
Radio
Altimeter
(LRRA)
BITE
Procedure,
34-33
TASK
801.

3)  If the radio altimeter display shows on the captain’s or F/O’s displays, then you corrected the fault.
　
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