King Air C90GTi, Pilot Training Manual

Page: 133 / 557

Even if the fuel does not contain water or
you have drained the water out, there is still
the possibility of fuel icing at very low tem-
peratures. The oil-to-fuel heat exchanger is
used to heat the fuel prior to entering the
fuel control unit. Since no temperature mea-
surement is available for fuel prior to the
h e a t ex c h a n g e r, t h e t e m p e r a t u r e m u s t b e
assumed to be the same as the outside air
temperature.
The graph in the Limitations section of the
Pilot’s Operating Handbook is used as a guide
in preflight planning, based on known or fore-
cast conditions, to determine operating tem-
peratures where icing at the fuel control unit
could occur. Enter the graph with the known
or forecast Outside Air Temperature and plot
vertically to the given pressure altitude. In
t h i s ex a m p l e ( Fi g u r e 5 - 1 5 ) , O u t s i d e A i r
Te m p e r a t u r e e q u a l s m i n u s t h i r t y d eg r e e s
Celsius and pressure altitude equals 5000
feet. Next, plot horizontally to determine the
minimum oil temperature required to prevent
icing. In this example, the minimum oil tem-
perature required is 38 deg rees Celsius. If
the plot should indicate that oil temperature
versus Outside Air Temperature is such that
ice formation could occur during takeoff or
in flight, anti-icing additive must be mixed
with the fuel.
The King Air maintains a constant oil tem-
perature, however, this temperature varies
from one aircraft to another. For most air-
craft the oil temperature will be between 50
and 60 deg rees Celsius. Compare the mini-
m u m o i l t e m p e r a t u r e o b t a i n e d f r o m t h i s
g raph with the oil temperature achieved by
each par ticular air plane involved. If the an-
ticipated actual oil temperature is not equal
to, or above this minimum temperature, anti-
icing additive confor ming to MIL-I-27686
or MIL-I-85470 must be added to the fuel.
Water in jet fuel also creates an environment
favorable to the growth of a microbiologi-
cal “sludge” in the settlement areas of the
fuel cells. This sludge, plus other contami-
nants in the fuel, can cause corrosion of metal
KING AIR C90GTi/C90GTx PILOT TRAINING MANUAL
5-16
FOR TRAINING PURPOSES ONLY
5
FUEL
SY
STEM
-60 -50 -40 -30
FUEL TEMPERATURE (OAT) ~ ˚C
MINIMUM OIL TEMPERATURE ~ ˚C
-20 -10 0
0
10
20
30
40
50
60
70
10
30,000
20,
000
10,00
0
PRESSURE ALTITU
DE ~
FEET
SL
Figure 5-15. Fuel Temperature Graph