DP

AND DIFFERENTIAL
NO. 4, NO. 5, NO. 9 ANDPRESSURE INDICATOR
EQUIPMENT
SIDE OF NOSE WHEEL WELL NO. 11 AND NO. 12 - LEFT SIDE
OF NOSE WHEEL WELLP/C PRESSURE CONTROLLER
Pitot Static System Schematic
Figure 2

STATIC PORT
COMBINED PITOT STATIC PROBE DRAIN FITTINGS STATIC LINE PITOT LINECAP

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 ú ú 13 Page 4 ú Mar 15/94
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
 4.  Pitot-Static Probe (Fig. 1)
__________________
 A.  The pitot-static probe is designed to accurately sense pitot (total) and static (altitude) pressure over the complete operating range of the airplane. The pitot-static probe consists of a probe and pressure sensing ports. A strut projects the probe several inches out from the fuselage and isolates the probe from the effects of fuselage variance. A baseplate contains the electrical and pressure fittings. Dowl locator pins are also installed on the baseplate to ensure accurate alignment of the installed probe.
 B.  Pitot pressure is sensed at an opening in the forward end of the probe. Static pressure ports are located in the contoured midsection of the probe: the contoured surface provides aerodynamic compensation to correct the static pressure position error caused by the airplane. The contour configuration and port locations minimize errors due to mach number and angle of attack.
 C.  An anti-icing heater is installed in each probe to prevent ice accumulation on the probe during flight. The heater is electrically connected to two terminal pins shielded in the baseplate of the probe. The heater is a self-regulating coaxial type. The temperature-compensating characteristic provides maximum power for in-flight operation, while automatically reducing the power in still-air conditions to prevent overheating. If the heater is energized at rated voltage during ground operation, the pitot static probe will become hot, and those areas which require high heat concentration may become discolored. This discoloration is normal and has no adverse effect on the unit. Maximum performance, accuracy and life will be obtained from the pitot-static probe by minimum amount of operation of the anti-icing heaters in still air.
 D.  Do not expose the pitot-static probe to contaminants; avoid solvents, lubricating oil and grease. Do not insert any object into the static port which could flare out the edge of the ports. If necessary to use fluids on the pitot-static probe, use fluids that evaporate without leaving harmful residue, such as water.
 5.  Alternate Static Port (Fig. 1)
_____________________
 A.  The alternate static ports sense static (ambient) pressure and provide the static pressure input to the alternate static system. The port is flush-mounted in a cutout in the fuselage skin. A circle is painted around the port with a caution note below. The area within the circle must be kept clean and smooth and the holes in the port must not be deformed or plugged. There are no provisions to heat the ports.
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 ú ú 11 Page 5 ú Mar 12/02

BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
 6.  Pitot-Static Drains (Fig. 1)
___________________
 A.  The drains allow the removal of moisture which has accumulated in the pitot and static pressure lines. This cylindrical shaped device terminates the vertical runs of pitot and static tubing. The drain consists of two parts (upper and lower). The upper part contains a spring-loaded seal that locks in place to protect the seal opening. The lower part is a bayonet cap that may be removed, turned upside down, and inserted into the upper part to open and drain the pressure line.
 B.  An identification label is located adjacent to the drain to indentify the line. A lanyard is provided to prevent loss of the cap when it is removed from the line.
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