Hydraulic System Operation

Ensures positive fluid flow to all hydraulic pumps.

LOW PRESSURE lights for both pumps (blinking), MASTER CAUTION (momentarily), HYD (momentarily).

Ailerons, Rudder, Elevators & Elevator feel, Flight spoilers (half).

Landing gear retraction, Ground spoilers.

Leading Edge Flaps & Slats retraction, Autobrakes.

Rudder, Thrust reversers, Leading Edge Flaps & Slats (extend only), Standby Yaw Damper.

EDP supplies roughly 6 times the fluid volume as EMDP.

RF (refill) appears when hydraulic fluid is below 76% and on the ground,engines off or flaps up after landing during taxi.

RF (refill) indicator displayed next to A or B quantity displays.

Perform M300 write-up and call Maintenance Control via Dispatch.

1675 lbs of fuel in main wing tanks is required for adequate hydraulic fluid cooling during ground operations of Electric Motor-Driven Pumps (EDMP).

If pushback is needed without a nose gear steering lockout pin, both system A hydraulic pumps must be switched OFF.

The PTU provides extra hydraulic fluid to operate flaps and slats normally when the system B engine-driven pump is not functioning.

The Power Transfer Unit (PTU) does not directly transfer hydraulic fluid. It uses system A pressure to drive a pump that pressurizes system B.

The PTU operates in the air when flaps are not in the up position and system B engine-driven pump pressure drops below limit.

The LGTU supplies the necessary hydraulic fluid to raise the landing gear at the normal rate if system A engine-driven pump volume is lost.

The LGTU is triggered during flight when engine 1 RPM drops below a threshold, the landing gear lever is in the UP position, and the main landing gear is not up and locked.

The Standby Hydraulic System is a backup system engaged if system A or B pressure drops.

The Standby Hydraulic System can be manually activated by moving either FLT CONTROL A or B switch to STBY RUD or moving the ALTERNATE FLAPS Master switch to ARM.

The Standby Hydraulic System automatically activates if the plane has flaps extended, exceeds wheel speed of 60 kts aloft, and either of the hydraulic systems A or B fails and Main rudder PCU Force Fight Monitor activates.

Hydraulic Systems A and B typically power the primary flight controls, such as ailerons, elevators, and rudder.

In the event of both Hydraulic Systems A and B failing, the ailerons and elevator are controlled mechanically through cables, while the rudder is controlled by the Standby Hydraulic System.

With Hydraulic System B failure, leading edge flaps and slats are controlled by the Standby Hydraulic System, while trailing edge flaps are controlled electrically.

If the aileron system is jammed, the spoilers can be used for roll control by applying force to the First Officer's control wheel.

If the spoiler system is jammed, the ailerons can be used for roll control by applying force to the Captain's control wheel.

Aileron trim is prohibited with the autopilot engaged because it is not reflected in the control wheel position, and any trim applied can result in abrupt rolling movements when the autopilot is disengaged.

Flight spoilers deflect when the control wheel displacement exceeds approximately 10 degrees.

The Elevator Jam Landing Assist system uses flight spoilers to adjust the descent rate during approach and landing. A push on the control column increases descent by extending spoilers, while a pull retracts them, decreasing descent.

To activate the Elevator Jam Landing Assist system, you must: 1) Select the Elevator Jam Landing Assist switch ON, 2) Have actual flaps extended to a position of 1 or greater, and 3) Disengage the autopilot.

With the autopilot engaged, stabilizer trim is controlled automatically through the autopilot stabilizer trim circuit. When flown manually, the main electric stabilizer trim switches on each control wheel engage the electric trim motor to adjust the stabilizer.

The Autopilot Trim or Main Electric Stabilizer Trim is active in the high-speed mode when flaps are extended and in the low-speed mode when flaps are retracted.

The STAB TRIM Cutout switches (PRI and B/U) on the control stand disconnect the stabilizer trim motor from inputs like Autopilot Trim, Main Electric Stabilizer Trim, and Speed Trim System when set to CUTOUT.

If the STAB TRIM Cutout switches are set to CUTOUT, you must manually rotate the stabilizer trim wheel to adjust the stabilizer.

The Control Column Actuated Stabilizer Trim Cutout switches interrupt the operation of Main Electric Stabilizer Trim, Autopilot Trim, and the Speed Trim function when the control column movement opposes the trim direction. It also interrupts MCAS nose-up trim commands during forward column movement, but not nose-down commands during aft movement.

The Flight Control Computer (FCC) software column cutout function prevents unwanted trim adjustments when the control column opposes the trim direction.

The Flight Control Computer (FCC) software column cutout function prevents unwanted trim adjustments when the control column opposes the trim direction.

A switch on the aft electronics panel that, when set to "OVRD", allows the Main Electric Stabilizer Trim to operate regardless of the control column position.

The Speed Trim System (STS) is designed to improve flight characteristics during operations with low gross weight, aft center of gravity, and high thrust. It achieves this by providing speed and pitch stability augmentation.

The Speed Trim (ST) function of the STS is designed to keep the aircraft at a trimmed speed. It works by commanding the stabilizer in a direction opposite the speed change, effectively returning the airplane to a trimmed speed.

The Maneuvering Characteristics Augmentation System (MCAS) is a pitch stability augmentation function that activates at elevated Angles Of Attack (AOAS). Its purpose is to increase control column forces by commanding the stabilizer in the nose-down direction, making it harder to stall.

The MCAS function operates under the following conditions: 1) Elevated Angles Of Attack (AOAS), 2) Autopilot not engaged, and 3) Other specific conditions.

The Speed Trim function operates under the following conditions: 1) Up to Mach 0.68, 2) 10 seconds after takeoff, 3) 5 seconds following release of the Main Electric Stabilizer Trim switches, 4) Autopilot not engaged, and 5) Sensing of trim requirement.

The Control Column Actuated Stabilizer Trim Cutout switches are designed to mitigate a latent failure of the Control Column Actuated Stabilizer Trim Cutout switches. They provide an extra layer of redundancy by cutting out automatic stabilizer commands beyond the cutout position of the switches.

If you attempt to takeoff with the stabilizer trim out of the green band, the Takeoff Warning horn will sound intermittently, and the TAKEOFF CONFIG light will illuminate.

The Speed Trim function controls the stabilizer trim motor at a high rate when the flaps are extended and at a low rate when the flaps are retracted.

The Speed Trim function is designed to improve flight characteristics during operations with low gross weight, aft center of gravity, and high thrust when the autopilot is not engaged.

This system uses hydraulic pressure to help the plane stay stable in the air, especially during turbulance, helping to prevent unwanted movements like dutch roll.

The Standby Hydraulic System provides a backup solution if the primary hydraulic systems fail, allowing the aircraft to maintain control of the rudder and access certain flight controls.

The flight control switches labeled "SPOILER A" and "B" are used for maintenance purposes only.

The AUTO SPEEDBRAKE system automatically deploys spoilers during landing or a rejected takeoff if certain conditions are met, such as the speedbrake lever being down, landing gear wheels spinning, and thrust levers being reduced to idle.

The SPEED BRAKE DO NOT ARM light illuminates when there is a fault within the auto speedbrake system, indicating that the system is not operating properly.

MCAS activates only when the autopilot is not engaged. It's designed to function independently to assist pilots in specific situations.

The Maneuvering Characteristics Augmentation System (MCAS) uses a high rate to control the stabilizer trim motor. This means it makes adjustments quickly to maintain stability.

The Flight Control Computer (FCC) receives data from both Angle of Attack (AOA) vanes to determine if MCAS needs to activate. It's getting input from two sources for accuracy.

To inhibit or reverse MCAS, pilots can use the Main Electric Stabilizer Trim switches. This gives them direct manual control over the stabilizer's movement.

MCAS cannot operate for 5 seconds after the pilot uses Main Electric Stabilizer Trim for inhibition. After the 5 seconds, MCAS can resume operation if needed based on the sensed angle of attack (AOA) and Mach.

The MCAS function has a limit on nose-down stabilizer trim movement to prevent excessive nose-down pitching and preserve the elevator's ability to control the aircraft's pitch.

When MCAS reaches its nose-down trim limit, the SPEED TRIM FAIL light illuminates. This indicates the Speed Trim System, including both MCAS and the Speed Trim function, is inhibited for the rest of the flight.

A failure in the Speed Trim System, either the Speed Trim function or MCAS, will cause the SPEED TRIM FAIL light to stay on even after a FLT CONT Master Caution is reset. It means the system is malfunctioning.

If the SPEED TRIM FAIL light only comes on during the RECALL phase of the FLT CONTROL master caution, and it goes off when the Master Caution is reset, it likely indicates a single Flight Control Computer (FCC) channel failure. You would not need to perform the QRH Non-Normal Checklist in this case.

Pilots can override the nose-up or nose-down stabilizer trim commands of the Speed Trim System by using the Main Electric Stabilizer Trim switches. This allows them to counteract the system's commands.

Ensures a continuous flow of hydraulic fluid to all hydraulic pumps.

The Standby Hydraulic System provides backup for the main systems, powering the rudder, thrust reversers, and some flap/slat functions. It's a critical safety feature in case of failure.

The LGTU activates to lift the landing gear when System A's pump fails, ensuring a safe landing.

The pilot activates the Standby Hydraulic System manually to regain control of the rudder or to extend flaps/slats. It's a quick and easy way to restore some functionality.

The hydraulic fluid, which cools and lubricates the electric motor-driven pump, has overheated.

The Power Transfer Unit (PTU) allows hydraulic fluid from System A to pressurize System B, ensuring flap/slat functionality even when the System B pump fails.

The Yaw Damper uses hydraulic pressure to stabilize the aircraft during turbulence, preventing excessive yaw movements.

Both System A and B power the primary flight controls (aileron, elevator, rudder) at the same time, providing redundancy.

The Speed Trim System (STS) improves aircraft stability during low weight/aft CG conditions by adjusting the stabilizer. It's like an automatic trim for specific situations.

The MCAS, activated by a high angle of attack, helps prevent stalls by adjusting the stabilizer to resist nose-up pitching. Think of it as an assistant preventing dangerous situations.

The Power Transfer Unit (PTU) is a system that provides additional hydraulic fluid to operate the Autoslats and Leading Edge Flaps & Slats at normal rates when the System B Engine-Driven Pump (EDP) is unavailable.

The PTU does not directly transfer hydraulic fluid. It uses System A pressure to power a hydraulic Motor-Driven Pump, which pressurizes System B hydraulic fluid.

The PTU operates when the aircraft is airborne, the flaps are not in the up position, and the System B Engine-Driven Pump (EDP) hydraulic pressure drops below its limit.

The Landing Gear Transfer Unit (LGTU) supplies the required hydraulic fluid to lift the landing gear at the normal rate when System A's Engine-Driven Pump (EDP) volume is lost.

The LGTU operates in flight when Engine 1 RPM drops below a threshold, the landing gear lever is in the UP position, and the main landing gear is not up and locked.

The Standby Hydraulic System is mainly used as a backup if both System A and/or B pressure is lost.