737 MAX Flight Crew Operations Manual
Flight Controls -
System Description
9.20.6
MN-FLT-OH-201
Pitch Control
The pitch control surfaces consist of hydraulically powered elevators and an
electrically powered stabilizer. The elevators are controlled by forward or aft
movement of the control column. The stabilizer is controlled by autopilot trim or
manual trim.
Elevators
The elevators provide pitch control around the airplane’s lateral axis. The
elevators are positioned by the pilots’ control columns. The A and B FLT
CONTROL switches control hydraulic shutoff valves for the elevators.
Cables connect the pilots’ control columns to elevator Power Control Units
(PCUs) which are powered by hydraulic system A and B. The elevators are
interconnected by a torque tube. With loss of hydraulic system A and B the
elevators can be mechanically positioned by forward or aft movement of the
pilots’ control columns. Control forces are higher due to friction and aerodynamic
loads.
Elevator Control Column Override Mechanism
In the event of a control column jam, an override mechanism allows the control
columns to be physically separated. Applying force against the jam will breakout
either the Captain’s or First Officer’s control column. Whichever column moves
freely after the breakout can provide adequate elevator control.
Although total available elevator travel is significantly reduced, there is sufficient
elevator travel available for landing flare. Column forces are higher and exceed
those experienced during manual reversion. If the jam exists during the landing
phase, higher forces are required to generate sufficient elevator control to flare for
landing. Stabilizer trim is available to counteract the sustained control column
force.
Elevator Jam Landing Assist System
If a jam occurs in the aft elevator control mechanism, both control columns have
a limited range of motion. During approach and landing, the Elevator Jam Landing
Assist System uses the flight spoilers for small changes to the flight path. To
activate the system, the Elevator Jam Landing Assist switch must be selected ON,
the actual flap position must be 1 or greater, and the autopilot must be disengaged.
With the system activated, the flight spoilers deploy to a preset position. The
control wheel steering force sensors detect forces applied to the control column.
A push on the control column causes the spoilers to extend farther, increasing the
descent rate. A pull on the control column causes the spoilers to retract, decreasing
the descent rate.
March 1, 2021