4. Pitot Static Probe
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 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 ports, which could flare out the edge of the ports. If necessary to use any fluids on the pitot static probe, use fluids that evaporate without leaving harmful residue, such as water.
5C8
34-11-01 Page 2 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. Feb 20/89
K85525
5C8 Pitot Static System Component Location
Feb 20/89 Figure 1 34-11-01
Page 3
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
Pitot Static System Schematic 5C8
34-11-01 Figure 2 Feb 20/89
Page 4
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
PITOT STATIC SYSTEM -MAINTENANCE PRACTICES
EFFECTIVITY
GJ B-2524
1. General
A. This section consists of procedures for flushing and draining the pitot static system. Flushing removes or assures the absence of any foreign matter in the pitot static system. Draining removes or assures the absence of any liquid collected in the pitot static system.
2. Pitot Static System Flushing
A. Flushing the system and checking system leakage tolerance of the pitot static systems may be carried out at the same time when deemed necessary. Flushing before every system leakage check is not normally required. Replacement of pitot static instruments or seal caps does not require flushing of the pitot static system.
B. Equipment and Materials
(1) Dry air pressure source, 0 to 15 pounds per square inch (gage) with filter and gage for measuring pressure
C. Prepare to Flush Pitot Static System
(1) Disconnect following hoses or tubes from the pitot static system, cap each hose or tube, remove quick-disconnect hose fittings and restrain all hoses to prevent whipping.
(a)
Disconnect hoses to captain's combined standby altimeter/airspeed indicator and cabin altimeter and differential pressure indicator.
(b)
In electronic compartment disconnect hoses to air data computers, air conditioning pressure controller, and flap load limiter airspeed switches.
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