ELECTRICAL DE-ICING SYSTEM MAINTENANCE:
Tests of the system must be carried out when the servicing schedule required it or when a component has been replaced. Typical tests are outlined below.
- Continuity and resistance checks should be carried out before the installation of a propeller or when the efficiency of an overshoe's heating surface is suspect. The values of resistance that the elements should have are laid down in the Maintenance Manual.
- Insulation checks are required to ensure that there is no breakdown of the element's insulation from the propeller blades or other metallic objects.
- Voltage proof checks are used to ensure that no insulation breakdown exists between the blade and heater element. They involve applying a high voltage between the blade and element and ensuring that no leakage exists. These checks are normally carried out after repairs to the overshoe.
- Functional tests of the ice protection system chan be carried out noting the current displayed for each of the phases of a.c. power on the flight deck ammeter. To prevent overheating of the elements the engine must maintain a minimum speed while the heating is on, as this allows a flow of air over the blades and engine intake. Some types of aircraft reduce the voltage of the system when the air / ground sense is in the ground mode and this lower voltage must be taken into account when monitoring the ammeter.