Ice and Rain Protection
A. Airfoil -Description and Operation
The deicer and vacuum system is operated with pressure obtained by topping off bleed air from the engine compressors. This air is routed through a regulator valve that is set to maintain the pressure required to inflate the deicer boots on the leading edge of each wing, the vertical stabilizer, and the horizontal stabilizer. To assure operation of the system should one engine fail, a check valve is incorporated in the bleed air line from each engine to prevent the escape of air pressure into the chamber of the inoperative compressor. High pressure air flows through an intercooler and check valvesto the pressure regulator/relief valve. The intercooler cools the bleed air temperature to a temperaturebelow 200°F. In the event the bleed air temperature exceeds 425°F, a bleed air overtemperatureswitch closes to illuminate the respective (left or right) BLEED AIR HOT annunciator light on the annunciator panel. The pressure regulator/relief valve regulates the pressure downstream to 18 psi and protects the system from overpressurizationif the regulated pressure exceeds 21 psi. The bleed air from the engine is also routed through an ejector that employs the venturi effect to produce vacuum for deflation of the deicer boots and operation of the instruments. The inflation and deflation phases of operation are controlled by means of a controlling deice valve.
Thedeicer system is actuated by a switch located on the RH overhead panel. This switch is a momentaryon switch. Deice boot inflation is indicated by blue WING and TAIL indicator lights on the right circuit breaker panel. Deice pressure can be monitored through the pneumatic pressure gauge located on the lower left instrument panel. Normally, the gauge should register in the green, but will flicker slightly during pneumatic deice operation.
The outboard wing deice boots will be referred to as the A boots and their controlling deice valve as the A deice valve. The inboard wing deice boots and the horizontal and vertical stabilizer deice boots will be referred to as the B boots and their controlling deice valve as the B valve.
Momentaryactuation of the SURFACE DEICEswitch provides power to the timer which initially opens the solenoid on the A deice valve. Airflow then passes through the A deice valve into the A boots. When A boot pressure reaches 15 psi (plus or minus 1 psi), a pressure switch closes to illuminate the blue WING indicator light. When the boots have been inflated for 6 seconds (plus or minus 0.5 second), the A boots exhaust throughthe deice valve, the indicator light extinguishes, and vacuum is restoredinto the A boots through the deice valve integral ejector. When the A circuit is deactivated by the timer, the B circuit is activated to open the B deice valve solenoid and begin inflation of the B deice boots. As system pressure reaches 15 psi (plus or minus 1 psi), the blue TAIL indicator light illuminates. After 6 seconds (plus or minus 0.5 second) of inflation, the timer deactivates the B deice circuit and the pressure is exhausted through the B deice valve. The indicator light extinguishes and vacuum is restored to the B boots through the integral ejector of the B deice valve. The pneumatic deice system will automatically shut down upon completionof one cycle of the A and B deice boots.
The deicer system on this airplane is equipped with a combination vacuum and pressure linefrom a combinationvacuum and pressure line from a central distributor valve to provide pressure for inflation and vacuum for deflation of the boots.
The vacuum linefor the instruments is routed through a suction reliefvalve that is designed to admit into the system the amountof air required to reduce venturivacuum sufficiently for proper operation of the instruments.
CAUTION: DO NOT OPERATE THE DEICER BOOTS BELOW -40°F. EXCEEDING THIS LIMIT CAN RESULT IN PERMANENT DAMAGE TO THE DEICERS.
EFFECTIVITY:
049990-10-00 PAGE
30-1 0-00 Jan 10/90
PIPERAIRCRAFT
PA-42-720 (Advanced Trainer)
MAINTENANCEMANUAL
A. Airfoil -Description and Operation (continued)
DeiceSchematic
Figure 1
Surface
EFFECTIVITY:
040-999
Jan 10/90 30-10-00
PIPERAIRCRAFT
PA-42-720(Advanced Trainer)
MAINTENANCEMANUAL
A. Airfoil-Description and Operation (continued)
CHART 1 (Sheet1 of 2) FAULTISOLATION (PNEUMATIC AIRFOIL DEICER SYSTEM)
Fault
