In many jet aircraft with conventional flight controls, the pilot and copilot-side primary flight controls are linked by torque tubes. This normally ensures both control columns move in unison in pitch and roll, and all ailerons, roll spoilers and elevators are actuated in a coordinated manner.
In case of a flight control malfunction were a jam occurs in one system, it is usually possible to split the controls, in some aircraft by pulling a flight control disconnect handle, in others the torque tube shears when a certain (high) load is applied to it.
X-Plane simulates both the type of failure and the flight control split to deal with it.
Control-jamming failures
Each of the primary controls can be jammed on either side, using the failure, or the failure datarefs:
sim/operation/failures/rel_ail_L_jam int y failure_enum roll control, left control column jammed
sim/operation/failures/rel_ail_R_jam int y failure_enum roll control, right control column jammed
sim/operation/failures/rel_elv_L_jam int y failure_enum pitch control, left control column jammed
sim/operation/failures/rel_elv_R_jam int y failure_enum pitch control, right control column jammed
Jamming either side will block the respective axis at its current deflection and prevent further movement until the controls are split.
Splitting and regaining control
On some airplanes, pitch and roll can be split separately, on others, the split affects both but they can be reconnected individually. X-Plane can simulate all of these situations by means of these datarefs:
sim/cockpit2/controls/torque_tube_split_roll int y boolean0 = Normal: Left and right roll input are connected, 1 = Disconnected, each joystick roll input for pilot or copilot goes to the respective side.
sim/cockpit2/controls/torque_tube_split_pitch int y enum 0 = Normal: Left and right pitch input are connected, 1 = Disconnected, each joystick pitch input for pilot or copilot goes to the respective side.
On some airplanes, these datarefs will only ever work in unison, while other airplanes might have separate handles to pull and therefore the datarefs can have individual values.
When the flight controls are split, the user’s joystick or yoke input will act on the pilot’s side only, and if a joystick input is configured for the copilot’s side, it will go the copilot’s side only.
For home use setups with only one set of flight control hardware, it is however possible to route the user input over to the copilot’s side by pressing and holding the priority button (normally the same command as the autopilot servo disconnect). By holding the priority button for 40 seconds, the user can effectively switch into the copilot’s seat and fly the copilot flight controls from the only connected joystick.
Roll spoiler actuation
A roll spoiler is a spoiler tab that goes up on the side the aileron goes up. Typically, it is linked to the on-side aileron only. That is, for a right turn, the right roll spoiler goes up as the right aileron deflects up. In case of a control split, initially only the spoiler on the side of the working aileron will be actuated, while the one on the side of the jammed aileron will not get a signal to operate, even though the spoiler control itself is not failed. In this case, the side with the working roll input can be chosen to actuate both sides of roll spoilers:
sim/cockpit2/controls/roll_spoiler_actuation int y enum 0 = Normal: left roll spoiler is controlled by left roll input, right roll spoiler is controlled by right roll input. 1 = Left: Both roll spoilers are controlled by the left aileron. 2 = Right: Both roll spoilers are controlled by the right aileron.
Operational example
Assume a jamming occurs somewhere in the right aileron control cables: sim/operation/failures/rel_ail_R_jam == 6
Now, the roll control is jammed and the ailerons cannot be moved.
The pilot pulls the flight control disconnect for the roll axis: sim/cockpit2/controls/torque_tube_split_roll = 1
Now, the pilot’s roll input acts on the left aileron only. Since the left aileron is not jammed, it will now deflect up or down responding to control input, and allow limited maneuvering while the right aileron remains locked in its jammed position.
In this situation left roll spoiler will work, the right won’t. Some airplanes allow the right roll spoiler operation to be restored by selecting sim/cockpit2/controls/roll_spoiler_actuation = 1