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757 MAINTENANCE MANUAL
PITOT PROBE ANTI-ICING - DESCRIPTION AND OPERATION
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General
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A. Four pitot probes (two on each side) are electrically heated to prevent erroneous readings due to ice conditions. Pitot probe anti-icing system components include: pitot probes, the auxiliary annunciator panel, and the miscellaneous test panel.
B. System electrical power comes from the 28-volt dc buses, and the 115-volt ac buses. Circuit breakers are on overhead circuit breaker panel P11, and main power distribution panel P6.
Component Details (Fig. 1)
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A. Pitot Probes
(1) Two pitot probes are located on each side, halfway down the fuselage, under the left and right No. 2 flight deck windows. Two levels of pitot probe heating are used, depending on whether the plane is on the ground or in flight.
B. Auxiliary Annunciator Panel
(1) Auxiliary annunciator panel M10394 is located on pilots' overhead panel P5. The annunciator panel contains four amber lights, one for each pitot probe. The lights are identified as: CAPT PITOT, F/O PITOT, L AUX PITOT, and R AUX PITOT. These lights come on to identify a probe heater failure.
C. Miscellaneous Test Panel
(1) Miscellaneous test panel M10398 provides for ground testing of the
probe heaters. The test panel is on right side panel P61.Operation
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A. Functional Description (Fig. 2)
(1)
Pitot probe heating is automatically controlled. This is done by action of air/ground relays, and relays whose position depends on engine speed from engine speed cards. The only action initiated from the flight deck is probe heater testing.
(2)
On the ground pitot probe heating depends on engine speed. If both engines are off, the ENG OUT relays are de-energized. The ENG OUT relays are controlled by engine speed cards in card file P50. (The ENG OUT relays associated with the CAPT and L AUX pitot probes are in left miscellaneous electrical equipment panel P36. The ENG OUT relays associated with the F/O and R AUX pitot probes are in right miscellaneous electrical equipment panel P37.) The circuit connecting electrical power to the probe heaters is open. The probes are not heated. This results in the current sensing relay (CSR) associated with each pitot probe heater to be de-energized. (The CSRs associated with the CAPT and L AUX pitot probes are in miscellaneous electrical equipment panel P33. The CSRs associated with the F/O and R AUX pitot probes are in P37.) This provides a closed path to ground for the pitot lights in the auxiliary annunciator panel. Therefore, on the ground with engines off, no pitot probes are heated, and all amber pitot lights on P5 are on.
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本文链接地址：757 AMM 飞机维护手册 防冰和排雨 CHAPTER 30 - ICE AND RAIN PROTECTION(86)
