Page 11-4
Pilot’s Operating Manual
Revision A1: Nov, 2002
Sub-section 11
ICE PROTECTION
Hawker 800XP Pro Line 21
Section III - SYSTEMS DESCRIPTION
De-icing fluid is drawn from the tank through a suction filter to the pump, and then via a pressure filter
and check valve to the head compensating valve. The head compensating valve ensures equal fluid
pressure at the wings and horizontal stabilizers proportioning units.
Fluid is fed from the head compensating valve to the three proportioning units, one located in each wing,
the other between the horizontal stabilizers. A check valve is incorporated in each proportioning unit
outlet to prevent back-flow when the system is inoperative. Each proportioning unit splits the main flow
down to the requirements of the individual distributor panels. This arrangement makes sure the fluid
supply is maintained to the remaining outlets should a pipe become disconnected.
At each distributor panel, fluid is fed through a metering tube into a cavity. From the cavity the fluid
passes through a micro-porous plastic sheet and through a titanium outer skin of greater porosity to
escape into the atmosphere. Airflow then causes the fluid to spread rearward over the wings and
horizontal stabilizer surfaces.
ROTARY-CUTTER ICE DETECTOR (Figure 1)
Formation of ice is detected automatically after takeoff and manual selection of the detector is available
for operation on the ground.
Power supplies to the ice detector are fed through the weight-on-wheels switch relay system and
controlled by an ICE DET AUTO-OVRD switch. With the switch selected to AUTO, the detector operates
when the airplane becomes airborne. Selecting the switch to OVRD by-passes the weight switch relay
so that the detector runs on the ground and in flight.
NOTE: The ICE DET switch should be selected to OVRD before taxiing in icing conditions.
The ice detector unit consists of an AC powered motor driving a serrated rotor which rotates in close
proximity to a fixed knife-edge cutter.
When ice forms on the rotor, the gap between the rotor and adjacent cutter is filled. The skimming action
of the cutter against the ice causes a rise in motor torque which rotates the motor slightly within its
mounting. Rotation of the motor actuates a microswitch which connects a DC power supply, via a time
delay relay, to illuminate an ICE DETECTED annunciator located on the overhead roof panel. The ice
warning is also indicated on the MWS by the illumination of the ICE PROT repeater annunciator.
Pushing an ICE DET TEST button illuminates both annunciators.
The time delay relay maintains the ice warning signal during intermittent rises in motor torque. When
ice ceases to form, a spring returns the motor to the normal position, the microswitch opens and after
a delay (60 seconds) the warning is cancelled.
WING SPOTLIGHTS (Figure 1)
Two spotlights, one on each wing fairing and controlled by a ICE ON-OFF switch, illuminates the left
and right wing leading edges for night visual inspection.
