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I have never worked on this type of aircraft, but I usually come across it in several hangars. I've been wondering on which mechanism this bulk door is lowered and lifted.

Is it by pneumatic system, hydraulic system or by electrical motors?

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From the EMB120 Ops Manual:

FORWARD ENTRY DOOR

The forward entry door incorporates a folding air stairs and is fixed at the fuselage's lower edge.

The door can be raised manually or hydraulically. For normal operation, two hydraulic actuators powered by the green hydraulic system or by an accumulator, raise the door. This actuator has the capability of performing four complete operations and is controlled from the INTERIOR FWD DOOR CONTROL PANEL (ATTENDANT'S PANEL) or from EXTERIOR FWD DOOR CONTROL PANEL. Each panel incorporates a pushbutton, which energizes a solenoid valve that allows hydraulic power to raise the door. A blue light illuminates while the door is moving up. This system's circuit breaker is located at the INTERIOR FWD DOOR CONTROL PANEL (ATTENDANT'S PANEL).

The door may be raised manually by an outside ground attendant who lifts the door to its closed position.

The spring accumulator is located in the hydraulic compartment at the right side of the fuselage forward section. Once the door is raised, moving the red inner or outer handle down will latch it. The hydraulic circuit provides a damping function when the door is opening.

The hydraulic circuit is provided with an emergency valve, which allows the forward door to be lowered when the solenoid valve fails.

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