Engine stall margin may be reduced
during high-altitude operation if the
fuel control density adjustment knob
is positioned to a lower density set-
ting than that recommended for type
of fuel being used.
Either of two types of fuel control units may
be installed on the engines. The fuel control
density adjustment knobs are different on each
of these units and are designated Type A and
Type B (Figure 5A-10). To make an adjust-
ment, push the knob in, rotate the knob to the
density setting desired, and release pressure.
If necessary, jiggle the knob until it locks.
The adjustment knob must be seated in its po-
sitioning detent for satisfactory operation.
AVIATION GASOLINE
Aviation gasoline (lowest octane available)
may be used as an emergency fuel provided its
use is limited to no more than 25 hours dur-
ing one engine overhaul period. Keep an ac-
curate record of engine operation time when
using this fuel. Mixing aviation gasoline with
jet fuel is allowed; all operation with avia-
tion gasoline in excess of 50% by volume must
be recorded in the Engine Log.
NOTE
Certain aviation gasoline and jet
f u e l r a t i o s c a n p r o d u c e g r e a t e r
flammability hazards under partially
filled airplane tank or storage tank
c o n d i t i o n s e n c o u n t e r e d d u r i n g
refueling or mixing. Follow estab-
lished safety standards to eliminate
any possible sparks.
ANTI-ICING ADDITIVE
Anti-icing additive conforming to MIL-I-
27686 must be added to all fuels for Learjet
operations. The additive concentration shall
be a minimum of .06% to a maximum of .15%
by volume.
Assure that the additive is directed into the
flowing fuel stream and that the additive flow
is started after fuel flow starts and is stopped
before fuel flow stops (Figure 5A-11). Due to
the chemical composition of fuel additives,
improper blending can cause deterioration of
fuel tank interior finishes and promote corro-
sion. Do not use less than one container (20
fluid ounces) of additive per 260 gallons of fuel
or more than one container of additive per 104
gallons of fuel. The blender (20 ounces) will
discharge completely in approximately four
minutes. Monitor the blender tube to assure that
additive flow is maintained. Do not allow con-
centrated additive to contact the coated inte-
rior of the fuel tank or the airplane’s painted
surfaces.
NOTE
Anti-ice additives may be harmful if
inhaled or swallowed. Use adequate
ventilation. Avoid contact with skin
and eyes. If sprayed into eyes, flush
with large amounts of water and con-
tact a physician immediately.
NOTE
Lack of anti-icing additive may cause
fuel filter icing and subsequent en-
gine flameout.
CAUTION
5A-15
FOR TRAINING PURPOSES ONLY
LEARJET 20 SERIES PILOT TRAINING MANUAL
FlightSafety
international
7
5
7
2
6
9
8
6
81
3
7
8
FU
EL ADJUS
T—
P
U
S
H
&
T
U
R
N
JP
-5
&
6
J
P
-4
–1
+1
+
2
+
3
+
4
—6
—5
—
4
—
3
—
2
INDEX
PIN
INDEX
PIN
TYPE B
TYPE A
Figure 5A-10. Fuel Density Adjustment