The 737 NG’s flight controls – general familiarisation

The 737 NG’s flight controls can be operated manually by pilots or automatically by the autopilot system.

Aileron: Pilots move the aileron control wheels, which manage cables linked to the aileron’s Power Control Units (PCUs). These PCUs then control the ailerons. The autopilot can also give inputs to these PCUs, indirectly moving the ailerons. Additionally, the ailerons work in tandem with the flight spoilers to assist in roll control.

Elevator: The control columns are linked via cables to the elevator PCUs, which manage the elevators. The autopilot can also provide inputs, moving the elevators accordingly.

Rudder: Pilots control the rudder using pedals. These pedals connect to cables that influence the rudder’s PCUs, which in turn move the rudder.

Flaps & Slats: The flap control lever governs the trailing edge flap control valve. When activated, hydraulic pressure powers the flaps, with follow-up cables ensuring correct positioning. Additionally, these cables manage the position of leading-edge devices, including flaps and slats.

Spoilers & Speed brakes: The speed brake lever controls the spoiler mixer. This mixer then manages the flight spoiler actuators and the ground spoiler control valve, which regulates the raising of the spoilers. The speed brake can also be automatically deployed by the autopilot.

Horizontal Stabilizer: The stabilizer trim wheels control a gearbox that adjusts the stabilizer position. There’s also an electric stabilizer trim switch and an autopilot input, both capable of influencing the stabilizer.

Flight Control Indications: These show the positions of the ailerons, elevators, and rudder. They appear as analogue indicators.

FDAU: The Flight Data Acquisition Unit gathers and standardizes data from multiple systems and sensors. This information is stored in the Flight Data Recorder and is also relayed to Display Electronics Units.

Position Transmitters: Various transmitters relay the positions of the ailerons, rudder, elevator, and spoilers to flight recorders or flight control computers.

Flight Controls Hydraulic Modular Packages: Located in the main landing gear wheel well, these packages control hydraulic pressure to primary flight controls and flight spoilers. They consist of shut-off valves, low-pressure warning switches, and a compensator cartridge. This cartridge ensures wind gust protection by maintaining return fluid pressure to control surfaces.

The 737 NG’s flight controls work through a combination of manual inputs, automated systems, hydraulic mechanisms, and electronic data acquisition and display units. Their integration ensures safe and efficient aircraft manoeuvrability.

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