S 216-004
(3)
Visually make a check that the support tubing attaches and the detector elements are installed correctly.
S 226-005
(4)
Examine the support tubing for dents or bent or twisted sections.
NOTE: Small dents which can occur to the tubing (up to 0.06 inch
____ depth) are permitted. But cracks or bent or twisted sections in the tubing are a cause to reject them.
S 226-006
(5)
Examine the detector elements for all bends less than the minimum bend radius of 1 inch.
S 216-011
(6)
Examine the elements for no bends nearer than 1 inch of the clamps and the flange assemblies.
(7)
Examine the detector elements for all worn areas and cuts.
S 216-007
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747-400 MAINTENANCE MANUAL
(8) S 216-012Permit lightly worn areas on the finish.
(9) S 216-013Reject the detectors with badly worn area or cuts.
S 096-008
WARNING: MAKE SURE YOU DO THE LOCK REMOVAL PROCEDURE (REF 32-00-30/201).
_______ FAST MOVEMENT OF THE DOORS FOR THE LANDING GEAR CAN CAUSE INJURY TO PERSONS OR DAMAGE TO EQUIPMENT.
(10) Remove the door locks on the wing and the body landing gear (AMM 32-00-30/201).
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747-400 MAINTENANCE MANUAL
DUCT LEAK DETECTION SYSTEM - DESCRIPTION AND OPERATION
______________________________________________________
1. General (Fig. 1)_______
A. The duct leak detection system uses thermal switches to find a leak or rupture in a bleed air duct. The switches are installed along the wing leading edges, wing strut areas, and center ducts in the air conditioning bay and wheel well area.
B. Nineteen thermal switches are installed in each wing leading edge along the pneumatic ducts (Fig. 1). Switches in the leading edge are set to close at 200°F. Two more switches are above each strut where structural materials permit higher temperatures, are set to close at 250°F. Two more thermal switches are installed in each nacelle strut above the pneumatic manifold. These switches are set to close at 300°F.
C. There are an additional thirty thermal switches along the center ducts in the air conditioning pack bay and wheel well areas. The thermal switches detect an overheat condition caused by leaks or ruptures in the bleed air ducts.
D. SL 26-041 THERMAL SWITCHES; The thermal switches are color coded to facilitate installation. The colors on the switches are a guide to the location of where the switches belong. The colors are shown below:
-Green, installed in the WLE,
-Yellow, installed in the Center Duct, and above the Struts.
-Red, installed on the Nacelle Strut.
E. At normal standby condition, all thermal switches are in the open position. An overheat condition caused by a leak or rupture in the pneumatic ducts causes the thermal switch to close and the EICAS messages to come on. The EICAS messages are shown below:
-
BLD DUCT LEAK C
-
BLD DUCT LEAK L
-
BLD DUCT LEAK R.
F. The system is tested by the FIRE/OVHT TEST button on the P5 pilot's overhead panel. The test button tests the wing leading edge overheat system, engine fire/overheat system, APU fire detection system, and lower cargo smoke detection system. The test button tests the circuit continuity of the systems.
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