BUCS Flashcards
BUCS Description
The BUCS is a single channel, non-redundant, fly-by-wire control system that can electronically operate all four control axes. The BUCS is modeled to duplicate the mechanical flight controls with-out the Stability Augmentation System (SAS) engaged.
ARDD
Automatic Roller Detent Device - is located on each control, in each crew sta-tion, to allow the controls to decouple in the event of a control jam. This system allows the controls to decou-ple regardless of where the jam takes place.
LVDT
Linear Variable Displacement Transducers - control position and actuator position to calculate the equivalent mechanical control command when in BUCS. Translates control motion into an electrical signal that is utilized by the FMC to provide SAS, CAS, BUCS, and hold mode functions.
RVDT
Rotary Variable Displacement Transducers (RVDT) are used to sense a decoupling of the ARDDs, and LVDTs are used to sense a mistrack and send control move-ment information to the FMC. The FMC electrically con-trols the BUCS servo valve on the primary side of the affected flight control actuator.
What is needed to operate BUCS?
The primary hydraulic system and the FMC must be operational for BUCS to operate.
Jammed control linkage
If a jam has occurred, the FMC will engage BUCS when one of the crewmembers disconnects the controls from the mechanical control linkage by decoupling via the ARDD.
Failure of the primary hydraulic system results in?
In the loss of all FMC SCAS (SAS, CAS, and BUCS).
How is BUCS controlled?
In the BUCS mode the mechanical controls are physically decoupled and control is now maintained through an electronic control loop consisting of the following components:
(a) FMC
(b) LVDT
(c) Electro-Hydraulic Valves
(d) Actuator Solenoids
Severance between crewstations
(a) In a severance between crewstations the CPG controls are free to move to mechanical stop. During a severance the BUCS FAIL Caution warning is issued to the crew.
(b) The PLT controls are still connected normally to the flight controls, and BUCS engagement is not authorized as there is no mistrack between the PLT LVDT and actuator Ram A LVDT.
(c) If the PLT is incapacitated or otherwise unable to fly the aircraft, the CPG can engage BUCS using his BUCS select trigger and fly using BUCS. Control cannot be transferred back to the PLT.
BUCS FAIL (AXIS)
severance between crew stations.
Action: PLT TAKE CONTROL OF AIRCRAFT IMMEDIATELY
BUCS will not automatically engage and it is imperative for the PLT assume control. In order for the CPG to assume aircraft control, the CPG will need to create a mistrack while simultaneously squeezing the BUCS Select Switch.
BUCS FAIL
FMC has determined that the BUCS is in a failed state and will not allow the system to activate.
BUCS ON PLT (AXIS)
Severance aft of the crew stations
Action: EITHER CREWMEMBER CAN ASSUME AIRCRAFT CONTROL
There is still direct mechanical linkage between crew stations. BUCS is ON only in the affected axis. Once the mistrack is sensed full authority will be phased in over the next 1 second.
BUCS ON (STATION)
Jam in one of the flight control axis’s
Action: CREWMEMBER WHO ROLLED THE ARDD HAS CONTROL IN THAT AXIS
One of the crewmembers must roll their ARDD in order for the FMC to activate BUCS. Once ARDD is rolled full authority will be phased in over the next 3 seconds.
