“It’s only September,” you’re probably thinking. It was 104° Fahrenheit in Wichita, Kansas, when I wrote this last month. Still, now’s the time to check and prepare your airplane’s ice protection systems—and yourself—for the coming season. Let’s look at the major types of ice protection systems and what you should do now to ensure they will be ready.
Deice boots
Inflatable rubber deice boots have been the standard aircraft deicing system for almost 100 years. They’re still ubiquitous in piston twins and most turboprops, and even some jets still employ pneumatic deice boots.
Pneumatic deicing boots remove ice by inflating at the pilot’s command, breaking up ice that has adhered to the wing, horizontal stabilizer and vertical stabilizer leading edges so the slipstream may blow away the ice. If there are holes in the boots or if internal issues prevent some or all of the boots from inflating, the system’s ability to remove ice is reduced. Also, any discrepancy with the surface deicing system invalidates the “flight in icing conditions” authority for certified airplanes. Don’t wait until you start picking up ice to ensure the system is working properly.
Refresher Training
Here’s how a typical Pilot’s Operating Handbook describes the operation of a pneumatic surface deice system:
Deice boots cemented to the leading edges of the wings, horizontal tail surfaces and vertical tail surface are operated by engine-driven pump pressure. Compressed air, after passing through the pressure 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, controls the system. When the switch is in the AUTO position the deice boots inflate for a period of approximately 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
Right Throttle – 2000 rpm
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
Right Throttle – IDLE
Left Throttle – 2000 rpm
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
Right Throttle – IDLE
Notes on system operation and checking
To check each engine’s ability to inflate the boots individually, 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.
There is also a caution in most airplanes equipped with pneumatic deice boots: operation of the surface deice system in ambient temperatures below -40 °C can cause permanent damage to the deice boots, so operation in that temperature range is prohibited.
- To check each engine’s ability to inflate the boots individually, 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.
- There is also a caution in most airplanes equipped with pneumatic deice boots: operation of the surface deice system in ambient temperatures below -40 °C can cause permanent damage to the deice boots, so operation in that temperature range is prohibited.
Common failures
The most common causes of deicing boot failure are leaks in the rubber and internal corrosion of air lines or valves. Regularly inspect the boots for nicks and cuts, and have them repaired before the boots are needed. Lubricate the boots with approved de-ice boot dressing regularly. Conduct the POH Surface Deice preflight test procedure at least monthly, even in warm weather, to check its operation and to inhibit corrosion by blowing condensation out of the pneumatic lines and valves. Check out the operation of your pneumatic deicing system now, so if anything’s wrong, you have time to fix it before a discrepancy affects your cold weather go/no-go decisions.
TKS-type systems
Several anti- and deice systems over the years have employed variations on this theme: through a series of finely holed metal panels affixed to airplane structure, spray or coat parts of the airplane with anti-icing fluids (usually alcohol) to prevent ice formation and remove ice that has already formed. This system was developed in World War II by British firm Tecalemit-Kilfrost-Sheepbridge Stokes, and although other firms now sell and support these systems, the liquid employed is still called TKS fluid. Similar to deice boots, the fluid in TKS-type systems is prohibited for use at temperatures colder than -40°C.
One POH Supplement for TKS-based ice protection includes this description of the system:
TKS Ice Protection System is a system that exudes a filmy ice protection fluid from porous panels on the leading edges of the aircraft. The fluid minimizes ice formation on all lifting surfaces, propeller blades, wings, wing struts, and horizontal and vertical stabilizers. When the system is activated in flight, the ice protection fluid flows back over the upper and lower surfaces of the area being protected and protects the leading edges from ice build-up
PROPELLER PROTECTION
A fluid slinger on the propeller provides ice protection for the propeller and generates further ice protection for the fuselage and forward surfaces. Two positive displacement, constant volume metering pumps supply fluid to the panels and propeller. Single and combined pump operation and timed pumping provide a range of flow rates for varied icing conditions. A single pump supplies TKS fluid to the windshield spray nozzles for clear visibility through the windshield.
WINDSHIELD SPRAYERS AND PUMP
The TKS Ice Protection System includes windshield protection through the installation of windshield sprayers located at the base of the left windshield. Ice protection fluid is supplied to the sprayers by an on-demand gear pump which is installed beneath the floor between the main landing gear cross tubes. When the momentary spring loaded WINDSHIELD Switch is activated, the pump runs for 4 seconds. In addition to providing flow for windshield ice protection, the pump also acts as a priming pump for the main metering pumps. In the event of a loss of system prime, the windshield pump may be activated to purge the system of any air between the main metering pumps and the fluid reservoir.
Preflight test
In a typical POH Supplement (Kodiak 100) the recommended TKS system test before flight in suspected icing conditions includes:
- Master switch ON
- Display/Backup button PRESS
(button out) - Windshield deice switch ON (momentary switch)
- Verify presence of Ice Protection Fluid from
windshield spray nozzles - Surface/Prop switch NORM
- Pump duty cycle (both pumps) VERIFY
30 seconds ON,
90 seconds OFF - Surface/Prop switch OFF
- Backup pump switch ON
- Metering pump VERIFY RUNS CONTINUOUSLY
- Backup pump switch OFF
11.Surface/Prop switch MAX and then HI
12.Metering pumps VERIFY BOTH PUMPS RUN
13.Pump duty cycle VERIFY
2 minutes ON, then - Metering pumps VERIFY RUN CONTINUOUSLY
My point: Preflight checks of ice protection systems can be detailed, requiring regular practice to become routine.
Any number of other anti- and deice systems may be installed on an aircraft and should be similarly checked. Heated pitot tubes, fuel vents, static ports, stall warning, angle of attack probes and similar items may not individually show enough of a change in electrical draw to be verified operational sitting in the pilot’s seat. You may need to turn these items on and then exit the aircraft, carefully checking that each is warm to the touch without burning yourself. Wear a thick glove or use a wet towel, not your bare hand, as these items build heat rapidly. For that same reason turn them off quickly so they do not overheat, not having the cooling airflow they depend upon in flight.
Non-TKS alcohol windshield deice may be tested using the POH or Supplement technique, very similar to the TKS test. Electrically heated windshields generally will show an increase in electrical load when activated. Often you’ll see the airplane’s magnetic compass swing when turning on and off an electric windshield, another indication it receives power. Windshield “hot plates” also depend on cooling airflow so turn on the windshield deice, note indications it is working and turn it right off again.
Non-TKS alcohol propellers also have a TKS-like check in the POH or Supplement. Electrothermal propeller deice usually uses a lot of electrical power, so much so that many systems have automatic timers that turn the electric props on and off when the cockpit propeller heat switch is on. Do not test electric props unless the engine(s) is/are running, otherwise the brushes and slip rings that transfer electricity to the spinning props may burn out. Instead, during engine run-up activate prop heat, then confirm they are running correctly by observing indications on a Prop Amps or similar gauge that correspond to the ON/OFF timer schedule in the POH or POH Supplement for that specific installation.
Preflighting the pilot
Now’s also the time to preflight yourself for the coming ice season. Start by reading the POH for the airplane you’ll fly. Focus on the Limitations, Emergency Procedures, Normal Procedures and Systems Description for ice protection systems. If you’re flying a TKS system check out the online training courses on the CAV Systems website at www.cav-systems.com/tks/training. NASA has free online ice training for pilots at https://aircrafticing.grc.nasa.gov, and there are several fee-based courses aimed primarily at pilots of “known ice” airplanes easily found in an online search.
Don’t wait until your first seasonal encounter with suspected airframe icing conditions to find out your ice protection systems are working and you know how to use them. Start ice refresher training and testing your anti- and deice systems now.
