ICE AND RAIN PROTECTION
Description
Aircraft Operations Manual
11.1
PAGE
2
Jun 01/17
2.
MAIN COMPONENTS AND SUBSYSTEMS
2.1
Wing and stabilizer (boot) de
−
ice
Wing and stabilizer de
−
icing is provided by conven-
tional inflatable boots located on the wing and lead-
ing edges.
Normal color of the boots are black but as an option
silver colored boots are available. On the silver col-
ored boots there are black stripes to improve ice
detection.
Pre
−
cooled and regulated engine bleed air from
both engines, supplied via the pneumatic system, is
used for de
−
icing. With Mod No 2310 installed HP
bleed valve will automatically be opened when
associated PL are below 64
PLA (min takeoff posi-
tion) and the CYCLING switch is placed in either
ONE CYCLE or CONT position provided the HP
Bleed Switch is in AUTO. Once activated the HP
BLD VALVES will be opened for 30 sec. to cover a
complete boot de
−
ice cycle. The bleed air flows via
a normally open shut
−
off valve, controlled by the
AIR SUPPLY ON/OFF switch, to a pressure regula-
tor in each nacelle. The regulator reduces the pres-
sure to 18 psi and contains an integral relief valve
preventing the pressure from exceeding 25 psi if the
regulator should become stuck open. An overheat
sensor is installed downstream of each regulator.
On a/c s/n 240
−
up (post Mod 2083) the regulator
reduces the pressure to 21 psi and contains an
integral relief valve preventing the pressure from
exceeding 27 psi if the regulator should become
stuck open.
NOTE
The sensor will cause a DE
−
ICE OV TEMP light to
come on whenever the temperature reaches 150
C
(300
F).
The regulated pressure is directed to a distribution
duct supplying all boots through three distribution
valves. The distribution valves are solenoid oper-
ated and located one in each nacelle for inboard
and outboard wing de
−
ice and one in the fin for sta-
bilizer deice.
On a/c s/n 240
−
up (post Mod 2083) the regu-
lated pressure is directed to a distribution duct
supplying all boots through five ejector flow con-
trol valves. The ejector flow control valves are
solenoid operated and located two in each na-
celle for inboard and outboard wing de
−
ice and
one in the fin for stabilizer de
−
ice.
NOTE
Integral with each distribution valve or ejector flow
control valve is an air ejector which passes a small
flow of regulated air overboard to create enough
suction to prevent the boots from inflating due to
aerodynamic lift when not pressurized. When a so-
lenoid in a distribution valve or ejector flow control
valve is energized, manually or by timer, it will shift
from suction to pressure and a rapid inflation of the
boot will occur, cracking accumulated ice. Upon
completion of the automatically controlled 6 se-
conds timing cycle, the solenoid is de
−
energized
and suction restored. In conditions of low tempera-
ture,
−
30
C and below, the rubber in the boots be-
comes stiff which results in the deflation sequence
being prolonged.
The sequence of boot inflation is maintained by a
timer control unit. Upon selection of either ONE
CYCLE or CONT a timer will cause each boot zone
to inflate in the following order: stabilizer, outboard
wing, inboard wing, and finally re
−
inflation of stabi-
lizer.
When CONT is selected this inflation cycle will be
repeated every third minute.
A Push button for each boot zone permits manual
override of the timer.
To monitor the boot de
−
ice system a TIMER light
comes on should either of the following faults be
detected:
−
No pressure is sensed downstream the valve
sequenced for opening within 4 seconds.
−
The activated timer gives no inflation signal.
−
The boots are not cycling.
−
Pressure remains on in the stabilizer boot zones
(AUTO CYCLING switch in CONT).
−
Pressure remains on in the stabilizer boot zones
when next cycle is activated (AUTO CYCLING
switch in ONE CYCLE).
