actuator position to calculate the equivalent mechanical
control command when in BUCS. The SPAD assemblies
incorporate two switch assemblies to sense a decoupling
of the SPADs and LVDTs are used to sense a mistrack
and send control movement information to the DASEC.
The DASEC electronically controls the BUCS servo valve
on the primary side of the affected flight control actuator.
The primary hydraulic system and the DASEC must be
operational for BUCS to operate.
When BUCS is engaged do not release
the flight controls until the flight has
been completed and the main rotor
has come to a complete stop. Force
trim may or may not be available in the
BUCS ON axis.
During the execution of the emergen-
cy procedure for either BUCS FAIL or
BUCS ON, the APU must be on prior to
engine shutdown to provide electrical
power to the DASEC.
BUCS can become engaged when a
mistrack between the controls and the
actuator is sensed. This commonly
occurs when external power is pro-
vided to the aircraft without hydraulic
power. Applying hydraulic power and
completing an DASEC FD/LS check
may clear the BUCS engagement.
When BUCS is engaged, the BUCS
ON caution/warning light will illuminate and DASE will dis-
engage in the affected axis (axes) resulting in ASE cau-
tion/warning light illuminating (ASE not applicable for col-
lective). Several types of engagements are possible and
are covered, by crewstation, in the following paragraphs.
A BUCS jam engagement in the aft cyclic
longitudinal control direction or in the
left or right pedal tail rotor control direc-
tion may result in limited control author-
ity (from the point of the jam) because
the actuator is unable to break the actua-
tor shear pin. The worst case jam condi-
tion in the longitudinal aft cyclic (jam oc-
curs at the actuator) will result in a 12%
aft control authority from the point of the
jam. Forward cyclic can break the shear
pin and gain full control. the yaw axis
may be limited to +/ 25% control author-
ity from the point of jam. If flight control
authority is insufficient for a hover, at-
tempt a rollon landing.
After a BUCS engagement and transition
to BUCS controlled flight, a flight con-
trols controllability check (small control
inputs in each axis to check for correct
response) should be conducted to es-
tablish if any other control axis has been
c. Control System Engagement Logic (Pilot
crewstation pilot flying the aircraft).
(1) Jams. A jam can occur anywhere in the flight
control system through malfunction or battle damage.
Should the pilot be unable to move the controls in one or
more axes, he should aggressively decouple into the ap-
propriate axis. The pilot can expect the control to displace
to full throw when the SPAD releases. The DASEC will
wash in full authority over a period of approximately three
(3) seconds allowing the pilot to center the controls and
transition to BUCS controlled flight. The BUCS ON and
ASE (ASE not applicable for collective) caution/warning
lights will illuminate. SAS will be OFF in the engaged axis.
Force trim will be available in all axes. Attitude/Hover hold
will be available in the axes that SAS is available.
(a) Severance aft of the pilots control. A
severance can occur due to malfunction or battle damage
between the pilots controls and the actuator. In this case
the BUCS will automatically engage when the pilot
achieves the sufficient mistrack with respect to RAM