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 C.  The pitot-static system supplies pitot and static pressure information to the standby altimeter, the standby airspeed indicator, the air data computers and the elevator feel computer.
 D.  The only electrical power required is for the heater circuits provided for anti-icing of the pitot-static probes. (Refer to Chapter 30-31-00, Pitot-Static, Temperature Probe and Angle of Attack Sensor Anti-Icing).
Pitot-Static Probe (Fig. 1)
__________________
 A.  Each of the four pitot-static probes provides one dynamic and two ambient pressure inputs to various pitot-static subsystems. Two probes are mounted on each side of the fuselage at STA 270 and STA 275.
 B.  Pitot pressure is sensed through a single pitot opening at the tip of the probe and connected to its respective subsystem inside the airplane through a tube and fitting with a hexnut marked P1.
 C.  Static pressure is sensed through two independent sets of static ports on the probe and connected to its respective static subsystem inside the airplane through two tubes and fittings with hexnuts marked S1 and S2.
Static Pressure Port (Fig. 1)
____________________
 A.  Four static pressure ports are used, two alternate static pressure ports and two dedicated static pressure ports.
 B.  Alternate Static Pressure Ports
 (1)  
Each of the two alternate static pressure ports is an independent sensor of external ambient air pressure for the alternate static system. The alternate static pressure ports are cross-connected.

 (2)  
The alternate static pressure ports are mounted low on each side of the fuselage at STA 680.

 C.  Dedicated Static Pressure Ports
 (1)  
The dedicated static pressure ports provide ambient pressure inputs to the elevator feel computer. The left dedicated static pressure port is connected to the left side of the elevator feel computer and the right dedicated static pressure port is connected to the right side of the elevator feel computer.

 (2)  
The dedicated static pressure ports are mounted on each side of the fuselage at STA 2367 just aft of the pressure bulkhead.

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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747-400
MAINTENANCE MANUAL

 D. There are no anti-icing heater provisions for the static pressure ports.
 4.  Source Select Valve (Fig. 1)
___________________
 A.  A static source select valve, located on the aft side of the floor beam at sta 440, provide the center air data computer with alternate pitot and static sources. The center air data computer normally receives pitot-static pressure inputs from the auxiliary No. 2 pitot system and auxiliary No. 1 static system. In the alternate position the center air data computer receives pitot-static pressure from the first officer's pitot system and the auxiliary No. 2 static system.
 B.  The valve is switched to the alternate position by setting the first officer's AIR DATA SOURCE SELECT switch on the P3 panel to C.
 5.  Drains (Fig. 1 and 2)
______
 A.  Drains are located on walls or uprights near the floor level of the lower decks of the airplane. They appear as small cylinders terminating vertical runs of pitot or static tubing. Drains are located in the left crawlway beside nose wheel well; in the right crawlway beside nose wheel well; in the electrical and electronics compartment; in the forward cargo compartment; in the bulk cargo compartment; and in section 48.
 B.  Two types of drain fittings are used in the pitot-static system. The drain assembly type is used on all drain lines except for those in section 48. The drain plug type is used on all lines in section 48.
 C.  The drain assembly is a two-part device with an upper half containing a seal spring-loaded in the closed position, and a lower half that locks in place to protect the seal opening. The lower portion of the drain assembly may be removed, turned upside down, and reinserted into the upper assembly. With the lower half held in this position by hand pressure, the seal in the upper half is held in the open position.
 D.  As installed, the drain acts as a sump. The drain assembly has a sight tube installed to indicate when liquid has collected in the drain. In the open position, the fitting functions as a drain allowing any collected material to pass out of the pitot-static tubing. Upon reassembly, it reverts to its function as a sump.
　
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