TIP TANK FUEL
JETTISON SYSTEM
(OPTIONAL)
A DC motor-driven valve in the tailcone of
each tip tank provides the capability of jetti-
soning tip tank fuel. One FUEL JTSN switch
on the fuel control panel controls both tip tank
jettison valves. When the FUEL JTSN switch
is placed to the ON position, the jettison valves
open and two amber lights illuminate contin-
uously on the fuel control panel, indicating that
the valves are fully open. The jettison tubes
are scarfed, which creates a low-pressure area
that helps pull the fuel out of the tank(s). This,
in combination with the force of gravity, en-
ables the entire contents of both tanks to be jet-
tisoned. Fuel jettison can be accomplished
with flaps and landing gear in any position and
at all speeds. Fuel jettison is faster while the
airplane is in a noseup attitude. It takes approx-
imately five minutes to jettison fuel from the
tip tanks.
NOTE
Jettisoned fuel is not recorded on
the fuel counter. Therefore, the fuel
counter reading should not be used
to compute fuel remaining or air-
plane weight after jettisoning fuel.
FUEL SERVICING
GENERAL
Fuel servicing includes those procedures neces-
sary for fueling and adding anti-icing additives.
Fueling is accomplished through a filler cap
in the top of each tip tank. Fuel then begins to
flow by gravity from the tip tanks into the
wing tanks as the tip tanks reach one-half full.
The wing standby pumps fill the fuselage tank
when the XFER–FILL switch is set to FILL.
At normal temperatures, some water is always
in solution (dissolved) with fuel. At high al-
titudes, fuel undergoes a cold-soaking process
and small amounts of water come out of the
solution and subsequently freeze. The anti-
icing additive specified for use in the Learjet
20 series must conform to MIL-I-27686. It
also prevents the growth of microbiological or-
ganisms in the fuel.
Safety Precautions
Refueling should be accomplished only in
areas which permit free movement of fire
equipment.
Ground fuel truck to apron and nose
gear uplatch spacer and ground fuel
nozzle to tip tank ground jack prior
to removing filler cap. This will pre-
clude possible fire and/or explosion
due to static electricity or sparks.
Figure 5-8 shows the airplane ground points.
When adding anti-icing inhibitor (Figure 5-9),
follow the instructions for blending found in
the AFM.
Hi-Flo Prist may be harmful if in-
haled or swallowed. Use adequate
ventilation. Avoid contact with skin
and eyes. If sprayed into eyes, flush
with large amounts of water and con-
tact physician immediately.
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