Thrust Reverser
Each
engine is equipped with a thrust reverser system that reduces stopping distance
and brake disc wear. The T/R’s reverse the fan airflow forward through blocker
doors, cascades and translating sleeves
The
left T/R uses hydraulic system A and the right, system B where they both are
able to receive standby hydraulic pressure when their respective hydraulic
system is unserviceable. Note that T/R use with standby pressure is of a lesser
rate so, losing one main hydraulic system will operate that side slower than
with main system pressure creating a possible swerve during reverser action.
The
T/R’s are controlled by the T/R levers on the thrust levers and operate when
< 10 ft RA or on the ground. The T/R operate when the thrust lever is at the
Idle position and the T/R handle is lifted to the interlock position when the
isolation valve positions to deploy the “translating sleeves”. The EEC’s
determine through a Linear variable differential transformer (LVDT) a 60%
opening of the two sleeves on each T/R, where after the mechanical interlock
releases and the levers can be lifted further to the Detent 1, 2 or MAX
position.
When the sleeves
move, the CDS shows the next message on the Upper DU.
• Amber REV when deploying or stowing
• Green REV when fully deployed
• Amber REV when deploying or stowing
• Green REV when fully deployed
When
stowing the T/R’s, the stow command is initiated by passing the 1 Detent
position which commands the T/R sleeves to stow. When the T/R lever is full
down and the sleeves at the 0% (closed) position, the isolation valve closes
and the locks engage.
During
normal operation the amber REVERSER light on the engine control panel
illuminates for 10 seconds without a MASTER CAUTION during a T/R stow operation
and extinguishes when the locks are engaged. The light will stay illuminated if
the T/R does not stow in 10 seconds, indicating a malfunction.
When the light
illuminates for more than 12 seconds a malfunction is detected and the ENG
annunciator and MASTER CAUTION light illuminates.
When
the down motion of the T/R levers is delayed for more than 18 seconds, the ENG
annunciator and MASTER CAUTION light illuminate and the locks will engage,
preventing further movement of the sleeves. To clear this situation you can
cycle the levers to the interlock position and back down.
When
a serious malfunction or disagree exists between the LVDT’s, the ENGINE CONTROL
light illuminates on the engine control panel together with a MASTER CAUTION.
When illuminated, it could mean a serious engine (EEC) malfunction or an LVDT
malfunction/disagree, when illuminated do not dispatch the aircraft.
Each
T/R translating sleeve has two deactivation points, installing two pins at
these points prevents T/R deployment. Follow the “thrust reverser deactivation
for flight dispatch procedure” from the current (AMM) manual to operate the
aircraft with deactivated T/R’s.
An auto–restow circuit compares actual reverser sleeve
position to the commanded position. When it determines an incomplete stowage or
uncommand movement of the sleeves to the deployed position, the circuit
commands to stow the T/R. When activated, the isolation valve remains open and
the control valve is held in the stowed position until the thrust reverser is
commanded to deploy.
