HYD Control Panel

Overview

The Hydraulic (HYD) Control Panel on the overhead panel allows the crew to monitor and control the aircraft’s three hydraulic systems: HYD 1, HYD 2, and HYD 3. Each system is equipped with electric or engine-driven pumps that can be manually controlled or set to automatic logic. The panel also includes SOV switches and a PTU control for redundancy and cross-system assistance.

Panel Components

HYD 1(2)A SOV Switch

This switch opens or closes the engine-driven pump (EDP) suction shutoff valve (SOV).
It is a pushbutton-type switch:
- When pushed, the corresponding engine SOV is open, allowing the EDP to draw hydraulic fluid.
- When released, the corresponding engine SOV is closed, isolating the EDP from the reservoir.

Warning

SOV control is important during fire conditions or maintenance.

HYD 1B Selector

Controls the electric pump for HYD 1B.
Three positions: OFF, AUTO, and ON.
- AUTO: The 1B pump operates automatically under these conditions:
  - Left engine is running and the 1A pump fails
  - Left engine fails in flight
  - Right engine runs with parking brake released and left engine off
  - During takeoff/climb or approach/landing (if PTU is in AUTO and 2A pump fails or right engine fails)
- ON: Forces 1B pump to run continuously.
- OFF: Pump remains off.

Note

1B pump will shut off if No.1 reservoir temp exceeds 116 °C and resumes only when below 104 °C via selector cycling.

HYD 3A Selector

Controls the electric pump for HYD 3A.
Three positions: OFF, AUTO, and ON.
- AUTO: The 3A pump operates automatically when:
  - Either engine is running
  - Aircraft is in flight
  - Emergency power supply is active
- ON: Pump runs continuously.
- OFF: Pump is off.

Warning

If reservoir temp exceeds 130 °C, the pump shuts off. Recovery requires selector cycling after temperature drops below 104 °C.

HYD 3B Selector

Controls the 3B electric pump, a backup to 3A.
Three positions: OFF, AUTO, and ON.
- AUTO: 3B pump activates under any of the following:
  - 3A pressure is below 1800 psi
  - Aircraft is in takeoff/climb or approach/landing
  - TAT < -35 °C
- ON: Pump runs continuously.
- OFF: Pump is off and 3B logic is disabled.

Note

If reservoir temp exceeds 130 °C and HYD 1 or 2 are healthy, 3B will shut off. It is restored only after selector cycling and cooling to <104 °C.

HYD PTU Selector

Controls the Power Transfer Unit (PTU), which transfers pressure between HYD 1 and HYD 2 without fluid transfer.
Three positions: OFF, AUTO, and ON.
- AUTO: PTU operates automatically if:
  - 1A pump is running, and either:
    - Right engine is running and 2A pump fails
    - Right engine fails in flight
    - Left engine is running with parking brake released and right engine not running
- ON: Forces PTU operation.
- OFF: PTU is disabled.

Note

PTU turns off if No.2 reservoir temperature exceeds 116 °C. It is restored automatically when below 102 °C.

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