Learjet 60 - Hydraulic Control Unit; Throttle Balk Solenoid

Pilot's' Manual
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Learjet 60
thrust range . Moving the thrust reverser lever above reverse idle
al-
lows the engine to spool up
providing the desired amount of reverse
thrust . The FADEC will schedule reverse thrust as a function of air-
speed (provided by ADC I and 2), decreasing thrust as the airplane
slows down . If airspeed data is not provided to the FADEC, the maxi-
mum reverse thrust available
will
be
65%
N1
.
THROTTLE BALK SOLENOID
A throttle balk solenoid is installed in
the
pedestal to
mechanically
pre-
vent either
thrust reverser lever from moving into the reverse range
until both thrust reversers are fully deployed . When the solenoid is de-
energized, a spring-loaded lockout mechanism allows the thrust re-
verser levers to move between the STOW
and DEPLOY positions only .
When energized, the solenoid will overcome the spring-loaded lockout
mechanism allowing the thrust reverser levers to move beyond the
DEPLOY position into the reverse thrust
range
.
HYDRAULIC CONTROL UNIT
The hydraulic control unit (HCU) functions as a shutoff valve to isolate
the thrust reverser system from the aircraft's hydraulic system
and also
as a selector valve
directing hydraulic fluid to stow and deploy the
thrust reverser doors as commanded .
The HCLi incorporates both a mechanical
and an electrical isolation
valve . The
mechanical valve may
be
manually closed and secured with
a locking pin thereby deactivating the thrust reversers . The electrical -
valve is closed until the conditions for arming are
satisfied or the
auto
stow sequence is initiated . The electrical
signals to operate the HCU
come
from the applicable thrust reverser relay box . On aircraft 60-097
and subsequent & prior aircraft inod~ied by SB 60-78-5 (Installation of
Thrust Reverser Hydraulic Control Re=lay Box), when the
left
or
right ENG
FIRE PULL T-handle is pulled, the associated
isolation valve will close,
shutting
off
hydraulic fluid to the associated thrust reverser .
A pressure switch, in the HCU, senses hydraulic
pressure availability
to the selector valve . When pressure is
present, the switch will turn on
the applicable TR
ARM light .
Each
HCU incorporates a check valve in the hydraulic
return port
which allows free flow from the HCU to
the
aircraft's
hydraulic return
system but no flow in
the
reverse
direction .