AIRPLANE
OPERATIONS
MANUAL
ICE AND RAIN
PROTECTION
REVISION 39
2-15-10
Page
9
Code
01
AOM-145/1114
WINDSHIELD HEATING SYSTEM
The windshields are electrically heated to prevent ice and fog formation
or for deicing and defogging purposes. Due to a higher thermal inertia
to bring heat to windshield inner layer, when Descent phase is initiated
the system must be turned ON to prevent fogging. During all the others
flight phases, the system must be kept OFF except when icing
conditions are anticipated or if situation requires. For airplanes
equipped with PPG windshield, the windshield heating system may be
selected ON during all flight phases.
The outer glass layer has no structural significance but provides a
rigid, hard and protected surface.
Windshield heating is accomplished through an electric conductive grid
embedded in its interlayer, which functions as an electric resistor.
Individual buttons located on the overhead panel control left and right
windshield heating. Separate power supplies are provided for each
windshield heating element and its control circuit.
Each windshield element is provided with three temperature sensors.
One sensor is used for temperature control and a second sensor is
used for overheat protection. A third sensor is provided as a spare for
use by maintenance personnel, should a failure occur in any of the two
sensors.
For airplanes Pre-Mod. SB 145-30-0033, each windshield element has
a dedicated temperature controller that receives a signal from the
associated temperature sensors and controls the windshield
temperature. When the temperature reaches the upper limit (45°C),
power supply to the heater is interrupted. When the temperature is
below the lower limit (40°C), power supply is automatically restored. A
caution message W/S HEAT FAIL is presented on the EICAS when a
system failure is detected or the windshield temperature exceeds
55°C.
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