King Air C90GTi, Pilot Training Manual

Page: 225 / 557

When the switch is tur ned on, the amme-
ter registers the amount of cur rent (18 to
24 amperes) passing through the system. If
the cur rent rises beyond the limitations, a
c i r c u i t - b r e a ke r sw i t c h o r c u r r e n t l i m i t e r
will shut off power to the deice timer. The
cur rent flows from the timer through the
br ush assemblies to the slip rings, where
it is distrib uted to the individual propeller
deicer boots.
Heat produced by the heating elements in the
deicer boots reduces the adhesion of the ice.
Adhesion thus reduced, the ice is removed
by t h e c e n t r i f u ga l e ff e c t o f t h e p r o p e l l e r
and the blast of the airstream.
NOTE
The heating sequences for the deice
boots noted in the following sec-
tion are the sequences which are in
evidence during normal operation.
Power to the deice boots is cycled in 90-sec-
ond phases. The f irst 90-second phase heats
all the deice boots on one propeller. The sec-
ond phase heats all the deice boots on the
opposite propeller. The deice time completes
one full cycle ever y three minutes. As the
deice timer moves from one phase to the next,
a slight momentar y deflection of the pro-
p e l l e r a m m e t e r n e e d l e m ay b e n o t e d .
Propeller deice must not be operated when
the propellers are static.
WINDSHIELD ANTI-ICE
SYSTEM
The pilot’s and copilot’s windshields each
have independent controls and heating cir-
cuits. The control switch allows the pilot to
select a high or a low intensity heat level.
The windshields are composed of three phys-
ical layers (Figure 10-4). The inner layer is
a thick panel of glass that acts as the struc-
tural member. The middle layer is a polyvinyl
sheet which car ries the f ine wire heating
grids. The outer layer is a protective layer of
glass bonded to the f irst two layers. The out-
side of the windshield is treated with a static
discharge f ilm called a “NESA coating.”
The windshields are protected against icing
by electrical heating elements (Figure 10-5).
The heating elements are connected at ter-
minal blocks in the corner of the glass to the
w i r i n g l e a d i n g t o t h e c o n t r o l s w i t c h e s
mounted in the pilot’s right subpanel.
A t r a n s p a r e n t m a t e r i a l ( u s u a l ly s t a n n i c
oxide) which has high electrical resistance
is incor porated in the laminations of each
w i n d s h i e l d, p i l o t ’s a n d c o p i l o t ’s . E a c h
w i n d s h i e l d i s a l s o f i t t e d w i t h e l e c t r i c a l
connections for the resistive material and
for temperature-sensing elements. The re-
sistive material is ar ranged so as to provide
p r i m a r y h e a t e d s u r f a c e s a n d s e c o n d a r y
heated surfaces.
PILOT and COPILOT WSHLD ANTI-ICE
switches in the ICE PROTECTION group on
the pilot’s inboard subpanel are used to con-
trol windshield heat (Figure 10-6). They have
positions labeled “NORMAL,” “OFF,” and
“ H I .” W h e n t h e P I L OT a n d C O P I L OT
switches are in the NORMAL (up) position,
the secondary areas of the windshields are
h e a t e d . W h e n t h e sw i t c h e s a r e i n t h e H I
( d ow n ) p o s i t i o n , t h e p r i m a r y a r e a s a r e
heated. The primary areas are smaller areas
and are heated faster to the same tempera-
tures as the NORMAL position.
KING AIR C90GTi/C90GTx PILOT TRAINING MANUAL
10-6
FOR TRAINING PURPOSES ONLY
10
ICE
AND
RAIN
PRO
TECTION
Figure 10-4. Windshield Installation