Page 8 - Sept24T

• 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 em- ployed 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 stabi- lizers. 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 pro- tection for the propeller and generates further ice protection for the fuselage and forward surfaces. Two positive displacement, constant volume meter- ing 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 protec- tion, the pump also acts as a priming pump for the main metering pumps. In the event of a loss of sys- tem 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 recom- mended TKS system test before flight in suspected icing conditions includes:
1. Master switch ................................ ON
2. Display/Backup button ................. PRESS
........................................................ (button out)
3. Windshield deice switch ............... ON (momentary
........................................................ switch) 4. Verify presence of Ice Protection Fluid from
windshield spray nozzles
5. Surface/Prop switch ..................... NORM
6. Pump duty cycle (both pumps) .... VERIFY ........................................................ 30 seconds ON, ........................................................ 90 seconds OFF
7. Surface/Prop switch ..................... OFF
8. Backup pump switch ..................... ON
9. Metering pump .............................. VERIFY RUNS ........................................................ CONTINUOUSLY
10. 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
14.Metering pumps ............................ VERIFY RUN ........................................................ CONTINUOUSLY
My point: Preflight checks of ice protection systems can be detailed, requiring regular practice to become routine.
Other systems
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 warn- ing, angle of attack probes and similar items may not
6 • TWIN & TURBINE / September 2024