System Description by Don Pierce: Electric Ice and Rain Protection

Six systems together make up electric ice and rain protection.

The Windshield Heat/Side Window Heat is controlled via the Windshield Heat Panel on the Pilots' Overhead Panel and six controllers - all located in the Forward Electronic Service Center (FESC). The panel has seven switchlights and a TEST switch. Two of the switchlights are labeled CAPT and F/O. They control heating for the two forward windshields. When the switchlights are latched in, IDLE is illuminated (switchlight position) and the windshield heat controller for the respective windshield is operative. There is no off position for the forward windshields; they are powered as long as there is electrical power applied to the plane. (Power can be removed for maintenance purposes by pulling the appropriate circuit breakers.) The temperature of the forward windshield is maintained at approximately 10°C. If power is applied to a cold windshield, the power is "ramped" slowly until windshield temperature is at approximately 10°C. When the switchlight is latched in, IDLE extinguishes and the temperature is now maintained at approximately 35°C. If windshield temperature reaches about 50°C, the amber FAULT light will illuminate and the controller will automatically remove power until the temperature is approximately 35°C, at which time power is again applied, maintaining temperature between 35 and 50°C. If, however, the temperature reaches 55°C, a fail-safe feature of the controller removes power completely; the associated circuit breaker on CB2 will open.



Side window heat control functions in a very different manner. The side window controllers even appear quite differently. In this case when a switchlight is unlatched, OFF will illuminate (switchlight position) and power is removed from the respective side wide heat system. Temperature is maintained at abut 35°C when the switchlight is latched in. As for the windshields, when temperature gets excessive, the FAULT light will illuminate and the respective controller will maintain temperature between 50°C and 35°C. However, there is no "fail-safe" protection as there is for the forward windshields. It is quite possible that some of the side window heat systems may be deactivated. If a system is deactivated, a placard (INOP or DEACT) should cover the appropriate switchlight(s).

The TEST switch is used to check for faults. The FAULT light will identify the faulty component in the system (the FAULT light stays on, flashes, or comes on and then goes out)

Each windshield and side window has three sensors, although only two are needed. If a sensor fails, wiring at the windshield (side window) can be swapped to allow continue use without changing the windshield (side window). However a second like failure requires a changeout.


Electrically heated air data sensors include four pitot probes (a primary and a secondary for the pilot and for the copilot), two Total Air Temperature probes (left and right sides) and two angle of attack sensors (left and right sides) The Air Data Sensor Heat System utilizes the AIR DATA SENSOR HEAT panel on the Pilots' Overheat Panel. The Heat panel has four switchlights and a MAST LIGHT INHIBIT switch.

Each pitot probe has two heating elements - one for the mast and one for the head. The head heater is a no-go item; It must be functioning to dispatch the plane. The OFF light should be extinguished when the switchlight is latched in, but if there is a failure in either of the two heater elements, the OFF light will re-illuminate - serving as a "fault" light. So if the OFF light illuminates the next step is to press the MAST LIGHT INHIBIT switch; if the OFF light extinguishes, it indicates that the failure in in the mast heater, and the plane may be dispatched. However, if the OFF light remains "on" it indicates that the failure is in the head heater and the plane may not be dispatched until the probe has been replaced.

The Total Air Temperature and Angle of Attack probes each have a single heater, and are powered when the respective TEMP PROBES or ALPHA switchlight is latched in. The OFF light in the ALPHA switchlight may remain on for a few seconds after latching the switchlight - until normal operating temperature is reached.



Another "electric" system, much simpler, is the windshield defog system. It is controlled via a DEFOG FAN switchlight on the Windshield Heat panel. The while ON light illuminates when the switchlight is latched in, signally the system to operate. The defog fan draws in cockpit air through an inlet near the copilot's feat. The air passes through the fan and four flexible distribution ducts to four louvered outlets at the base of the two forward windshields. The fan runs as long as the switchlight is latched in.


The Rain Repellent system consist of push-bullton switches on the Captain's and First Officer's Wiper Panel (Pilots' Overhead Panel), two nozzle assemblies per side and a single rain repellent bottle (aerosol cannister) - located in the cockpit. Each press of the push button switch will release about 20cc of Rainboe Type III fluid through the valve/timer/nozzle assemblies. The cannister should be replaced when either a REFILL float is in view or when cannister pressure is less than 45 psi. - there is a pressure gage by the threaded bottle. The gage has a red band from 0 - 45 psi, and a green band from 45 - 200 psi.

The Windshield Washer system is controlled via a single WASHER push button switch on the Captain's Wiper Panel. It is a latching switch (not a switchlight) which supplies power to a pump in a reservoir located in the FESC. The pump supplies the washer fluid through four spray nozzles (two per windshield). The pump does not have an auto-shutoff feature, but there is a float ball in the reservoir that is visible whenever the reservoir is half-empty and should be serviced.

Windshield Wipers are available for both the pilot and copilot. There is a three-position rotary switch (OFF/LOW/HIGH) on both WIPER panels (on the Pilots' Overhead Panel). The wiper blades "park" off the glass on the windshield frame. When a wiper selector switch is moved from OFF to LOW or HIGH, the blade moves from the park position onto the glass, and the "wipes" back and forth at the selected speed. When the selector switch is moved back to the OFF position, the wiper will revert to the "low" speed to return the blade back to the point where the "park motor" will move the blade off the glass and to the "park" position. (Each wiper assembly has two motors - a park motor and a wiper motor.)

Don