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747-400 MAINTENANCE MANUAL
(b) Remove the screws that attach relays B405 and B119 and the spacers to the panel.
S 024-024
(3) Remove the left glide slope coaxial relay:
(a)
Disconnect the coaxial cables and electrical cable from the relay
(b)
Remove the screws that attach relay B404 to the bottom of the panel.
TASK 34-31-06-404-025
3. Glide Slope Antenna Coaxial Relay Installation______________________________________________
A. General
(1)
There are three glide slope antenna coaxial relays installed on the forward side of the P31 panel STA 400 bulkhead. The equipment numbers are B404 for the left, B405 for the right, and B119 for the center coaxial relays.
(2)
Relay B405 is installed on top of relay B119. Relay B404 is attached to the bottom of the P31 panel.
B. Standard Tools and Equipment
(1) Resistance measuring bridge or ohmmeter that can measure 0.010 ohm with an accuracy of |0.001 ohm
C. Consumable Materials
(1)
B00316 Solvent - Aliphatic Naphtha TT-N-95
(2)
G00009 Corrosion Preventive Compound (Dow Corning No. 4) - BMS 3-23
(3)
G00033 Woven Cheesecloth - BMS 15-5
D. References
(1)
20-11-14/701, Metal Surfaces
(2)
20-22-01/601, Electrical Bonding
(3)
24-22-00/201, Manual Control
(4)
34-31-00/501, Instrument Landing System
(5)
51-21-03/701, Corrosion (Removal and Control)
(6)
51-24-13/701, Water Displacing Corrosion Preventive Compound
(7)
IPC 34-31-05 Fig. 1
E. Access
(1) Location Zone 115 Area Between Nose Gear Well and Fuselage, LH
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F. Procedure
S 864-026
(1) Make sure these circuit breakers are open with DO-NOT-CLOSE tags attached:
(a) P7 Overhead Circuit Breaker Panel
1) 7D22 ILS ANT SW L
2) 7D23 ILS ANT SW C
3) 7D24 ILS ANT SW R
S 114-028
(2) Clean the mating surfaces of the relay and airplane structure (Ref 20-11-14/701):
CAUTION:_______APPLY THE SOLVENT TO MATING SURFACES ONLY. MAKE SURE YOU RUB OFF THE SOLVENT FROM OTHER SURFACES. IF THE SOLVENT STAYS ON A SURFACE FOR A LONG TIME, IT CAN CAUSE DAMAGE TO THE SURFACE FINISH.
(a)
Apply aliphatic naphtha TT-N-95 solvent to the mating surfaces of the coaxial relay and airplane structure with a clean BMS 15-5 cloth. Use light pressure (Ref 51-21-03/701).
(b)
Use a clean cloth and clean the surface again.
(c)
Do these two steps until the metal of the bonding surfaces is bright, clean, and dry.
S 394-029
(3)
Apply a layer of BMS 3-23 corrosion-preventive compound to the mating surfaces (Ref 51-24-13/701).
S 424-027
(4)
Install the center glide slope antenna coaxial relay:
(a) Align relays B119 and B405 and the spacers with the holes in the P31 panel
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A 747-400 MAINTENANCE MANUAL
(b) Install the screws to attach relays B119 and B405 to the airplane.
S 764-030
(5) Measure the resistance between the relay switch case and the airplane structure (Ref 20-22-01/601). The resistance must be 0.01 ohm maximum.
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