Page 7 - Sept24T

regulators, goes to the distributor manifold. When the deice system is not in operation, the distributor valve applies vacuum to the boots to deflate and hold the boots flat against the surface. Then, when the deice system is operated, the distributor valve changes from vacuum to pressure and the boots inflate. As the cycle is completed, the valve returns to vacuum hold-down.
A three-position, spring-loaded switch, with a center OFF position, a down MAN (manual inflate) position, and an up SURFACE AUTO position, con- trols the system. When the switch is in the AUTO position the deice boots inflate for a period of ap- proximately 12 seconds, then deflate automatically and return to the vacuum hold-down position. The switch must be tripped for each complete cycle. The MAN (manual) position will inflate the boots only as long as the switch is manually engaged. When the switch is released, the boots deflate.
Preflight test
SURFACE DEICE SYSTEM
1. Right Throttle – 2000 rpm
2. Surface De-ice Switch — SURFACE AUTO [up] and RELEASE
a. Check visually for boot inflation and 15 PSI minimum deice pressure
b. Check visually for hold-down [boot deflation] when cycle is complete
3. Right Throttle – IDLE
4. Left Throttle – 2000 rpm
5. Surface De-ice Switch – MAN [down] UNTIL PRESSURE PEAKS (not more than 8 seconds), then RELEASE
a. Check visually for boot inflation and 15 PSI minimum deice pressure
b. Check visually for hold-down [boot deflation] when cycle is complete
6. Right Throttle – IDLE
Notes on system operation and checking
• To check each engine’s ability to inflate the boots in- dividually, you’ll run the test twice, once per engine. You may need up to 2000 engine rpm to provide enough pneumatic pressure to run the system.
• Some POHs do not include the one-engine-at-a-time check or the test of the manual inflation system. But testing the system completely is a good idea if you’re expecting an aerial icing encounter.
• The distributor valve is normally aligned with the pneumatic airflow, so pressurized air dumps overboard. The motion of pressurized air past a vent in the valve creates suction that pulls the deice boots in against the
•
leading edges. When the pilot activates the boots (AUTO or MAN) the switch sends electricity to the valve and rotates it so the pressurized air flows through the lines to the boots, inflating them. When the timer runs out (AUTO operation), or the pilot releases the switch from the MAN(dual) position, electrical power is removed from the valve, and it is spring-loaded back into the normal, inline position.
There may be an abnormal procedure checklist in the Emergency Procedures section for a condition when the boots fail to deflate after an AUTO or MAN inflation. It usually calls for pulling the Surface Deice or similarly labeled circuit breaker. This removes power from the distributor valve and causes it to rotate to the vacuum (hold-down) position (the most likely problem being continued electrical flow to the valve when it should be shut off). If you subsequently need to reactive the boots, the checklist says, you can reset the breaker to inflate the boots and pull it again to deflate, using the breaker itself as a manual surface deice switch.
September 2024 / TWIN & TURBINE • 5
Diagram of a typical pneumatic surface deicing system (Beech Baron 58 Pilot’s Operating Handbook)