737 MAX Flight Controls Questions

In general terms, how are the primary flight controls (ailerons, elevator, rudder) actuated on this type?

• Through a cable-and-pulley system linked to hydraulically powered control units, retaining the ability to fly using aerodynamic (manual reversion) control if hydraulic power to those surfaces is lost
• Entirely by fly-by-wire, with no mechanical cable linkage to the control surfaces at all
• By direct pilot muscle force alone, with no hydraulic assistance under any condition
• Only the rudder is cable-actuated, while the ailerons and elevator are fully fly-by-wire

Explanation: This type retains a mechanical cable-and-pulley control system linking the flight deck controls to hydraulically powered control units at the surfaces, and it's designed so that - if hydraulic power to those surfaces is lost - the crew can still move the control surfaces using aerodynamic (manual reversion) force alone, as a last-resort backup.

Flight Controls - Primary Control Actuation

What is the general purpose of the manual trim wheels located on the center console?

• They are mechanically connected to the horizontal stabilizer trim mechanism, letting the crew trim the aircraft by hand even without electrical power
• They are a purely cosmetic, non-functional cockpit feature
• They control rudder trim only, never pitch trim
• They can only be used while the autopilot is engaged

Explanation: The trim wheels are mechanically linked directly to the horizontal stabilizer trim mechanism, so the crew can adjust pitch trim by hand-cranking them even if electric trim power is unavailable - a direct, purely mechanical backup trim method.

Flight Controls - Manual Trim Wheels

What is the general distinction between 'flight spoilers' and 'ground spoilers' on this type?

• Flight spoilers can deploy in the air (assisting roll control and acting as a speed brake), while ground spoilers are intended to deploy automatically only after touchdown or during a rejected takeoff
• There is no distinction; both terms describe exactly the same panels used only on the ground
• Ground spoilers are used only in flight, never during the landing roll
• Flight spoilers can only be armed, never manually deployed by the crew

Explanation: Flight spoilers are usable in the air - helping with roll control and serving as an airborne speed brake - while ground spoilers are specifically intended to deploy automatically once weight is on the wheels (or during a rejected takeoff), to dump lift and increase drag for braking, and are not intended for airborne use.

Flight Controls - Flight & Ground Spoilers

Why do hydraulically-boosted flight controls typically include an artificial 'feel' system, rather than leaving the pilot to feel only what the hydraulic actuators themselves transmit?

• Hydraulic boost largely masks the real aerodynamic forces on the control surfaces, so an artificial feel system generates a synthetic resistance (varying with airspeed/configuration) to give the pilot meaningful tactile feedback
• Artificial feel exists purely for passenger comfort, with no connection to the pilot's controls
• Feel systems are used only on aircraft with no hydraulic boost at all
• It has no real purpose and is included only for symmetry between the two control columns

Explanation: Because hydraulic boost does most of the actual work of moving the control surfaces, the pilot would otherwise feel very little of the real aerodynamic load; an artificial feel system generates a synthetic resistance on the controls - typically increasing with airspeed - so the pilot still gets meaningful, speed-appropriate tactile feedback rather than an unnaturally light or constant feel.

Flight Controls - Artificial Feel System

Leading edge slats and Krueger-type flaps are typically actuated by which general power source?

• Hydraulic (or, as a backup on some systems, pneumatic) power, driven through a common drive shaft/gearbox arrangement across the wing
• Purely by aerodynamic forces alone, with no powered actuation at all
• By a separate battery-powered electric motor for each individual panel with no shared drive
• By manual pilot force transmitted directly with no mechanical assistance

Explanation: Leading edge devices are typically driven hydraulically (with a pneumatic backup drive on some designs) through a shared drive shaft and gearbox arrangement running along the wing, so all the leading edge panels extend and retract together in a coordinated way rather than each needing its own independent actuator.

Flight Controls - Leading Edge Device Actuation

What is the general purpose of a yaw damper?

• It automatically commands small rudder inputs to damp out Dutch roll oscillations, improving ride comfort and handling without requiring constant pilot correction
• It permanently locks the rudder in a fixed position
• It only operates when the landing gear is down
• It increases, rather than reduces, any yaw oscillation

Explanation: A yaw damper senses the onset of a Dutch roll-type oscillation and automatically applies small, timely rudder inputs to counteract it, damping the oscillation out - sparing the pilot from having to continuously make manual rudder corrections to keep the ride smooth and coordinated.

Flight Controls - Yaw Damper

Why are the two pilots' control columns (and rudder pedals) mechanically interconnected rather than independent?

• So a control input made by either pilot is automatically felt and mirrored at the other's controls, keeping both pilots aware of what's being commanded and allowing either to fly the aircraft
• Interconnection is done purely to save manufacturing cost with no operational purpose
• It prevents either pilot from ever moving the controls without the other's simultaneous input
• Only the rudder pedals are interconnected; the control columns are fully independent

Explanation: Mechanically linking both pilots' control columns and rudder pedals means an input from either side is transmitted to the other, so both pilots feel and can monitor what's being commanded - and either pilot retains full ability to fly the aircraft, including taking over from the other if needed.

Flight Controls - Interconnected Dual Controls

What is a general backup method for extending trailing edge flaps if the normal hydraulic flap drive is unavailable?

• An alternate (often electrically powered, lower-rate) flap extension system that can drive the flaps down independently of the primary hydraulic drive
• The flaps cannot be extended by any means other than the primary hydraulic drive
• The crew must manually push the flap surfaces by hand from outside the aircraft
• Flaps automatically extend fully the instant hydraulic pressure is lost

Explanation: An alternate flap extension system - commonly electrically driven and running at a slower rate than the primary hydraulic drive - gives the crew a way to get the flaps down for landing even if the normal hydraulic flap drive isn't available, trading speed of extension for continued availability of the function.

Flight Controls - Alternate Flap Extension