16 Questions
What is the primary power source used for extending and retracting most aircraft undercarriage assemblies?
Combination of hydraulic and electrical power
What is the purpose of the up-lock and down-lock micro-switches in the electrical undercarriage system?
To ensure all undercarriage legs are fully down and locked or up and locked
What is the voltage of the direct current supply to the motor in the electrical undercarriage system?
28 volts
What is the purpose of the ground safety micro-switch in the electrical undercarriage system?
To prevent accidental retraction of the landing gear while on the ground
How are the up-lock and down-lock micro-switches connected to each other?
In parallel
What method can be used to achieve emergency extension of the landing gear?
Back-up hydraulic systems, pneumatics, mechanical crank systems, or gravity systems
What is the primary function of the landing gear control lever?
To control the extension and retraction of the landing gear
How many undercarriage legs have their own set of up-lock and down-lock micro-switches?
Three
When is the safety micro-switch closed?
When the aircraft is in the air
What happens when the pilot moves the landing gear control lever to the 'up' position?
28 VDC is supplied to the 'up' winding of the motor
What happens when each landing gear leg begins to move?
The contacts of the down-lock micro-switches close
What happens when all three up-lock micro-switches open?
The DC voltage supply to the 'up' winding of the motor is interrupted
What is the purpose of the safety micro-switch?
To prevent accidental landing gear retraction
What is the sequence of events to retract the landing gear?
Weight of the aircraft comes off the landing gear, then pilot moves the landing gear control lever to the 'up' position
What is the function of the landing gear 'up' relay?
To supply 28 VDC to the 'up' winding of the motor
What is the purpose of the down-lock micro-switches?
To position the 'down' winding circuit of the motor
Study Notes
Extension and Retraction Methods
- Most aircraft undercarriage assemblies use a combination of hydraulic and electrical power for extension and retraction.
- Emergency extension can be achieved through back-up hydraulic systems, pneumatics, mechanical crank systems, or gravity systems.
Electrical Undercarriage Systems
- Electrical undercarriage systems enable the landing gear to be extended and retracted by one motor.
- The system consists of a 28V DC supply, motor, landing gear control lever, landing gear up and down relays, up-lock and down-lock position micro-switches, and a ground safety micro-switch.
- Each undercarriage leg has its own set of up-lock and down-lock micro-switches connected in parallel to ensure power availability until all legs are fully down and locked or up and locked.
Retraction
- After take-off, the aircraft's weight comes off the landing gear, allowing the shock absorber struts to fully extend, closing the ground safety micro-switch.
- When the pilot moves the landing gear control lever to the 'up' position, 28V DC is supplied to the coil of the landing gear 'up' relay, completing the circuit to supply 28V DC to the 'up' winding of the motor.
- The motor turns, driving the gearbox to retract the landing gear, and each landing gear leg begins to move, automatically closing the contacts of its down-lock micro-switch.
- When each landing gear leg reaches the fully retracted position, the respective up-lock micro-switch is actuated, opening its contacts, and deactivating the landing gear 'up' relay.
- With all three up-lock micro-switches open, the DC voltage supply to the 'up' winding of the motor is interrupted, positioning the 'down' winding circuit of the motor for landing gear extension.
This quiz covers the extension and retraction methods used in aircraft undercarriage assemblies, including hydraulic, electrical, and emergency systems.
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