Multi-Engine Oral Exam Guide by Michael D. Hayes

Author:Michael D. Hayes
Language: eng
Format: epub
Publisher: Aviation Supplies and Academics, Inc.
Published: 2012-08-21T00:00:00+00:00

D. Landing Gear

1. Describe how an “electric” landing gear extension/retraction system works. (FAA-H-8083-3)

This system uses an electrically driven motor for gear operation and is basically an electrically driven jack for raising and lowering the gear. When a switch in the cockpit is moved to the UP position, the electric motor operates. Through a system of shafts, gears, adapters, etc., a force is transmitted to the drag strut linkages and the gear retracts and locks. Struts are also activated that open and close the gear doors. If the switch is moved to the DOWN position, the motor reverses and the gear moves down and locks. Once activated the gear motor will continue to operate until an up or down limit switch on the motor’s gearbox is tripped.

2. Describe how a “hydraulic” landing gear system works. (FAA-H-8083-3)

This system uses pressurized hydraulic fluid to actuate linkages to raise and lower the gear. When a switch in the cockpit is moved to the UP position, hydraulic fluid is directed into the gear up line. The fluid flows through sequenced valves and downlocks to the gear actuating cylinders. A similar process occurs during gear extension. The pump which pressurizes the fluid in the system can be either engine driven or electrically powered. If an electrically powered pump is used to pressurize the fluid, the system is referred to as an electro-hydraulic system.

3. What are hydraulic limit switches? (FAA-H-8083-3)

Limit switches regulate the hydraulic pressure; they de-energize the hydraulic pump after the landing gear has completed its gear cycle. In the event of limit switch failure, a backup pressure relief valve activates to relieve excess system pressure.

4. What mechanism keeps the landing gear locked in the “up” position? (AFM/POH)

Some aircraft have uplocks; others use hydraulic pressure to keep the gear in the up and locked position.

5. What conditions will cause the gear warning horn to sound? (FAA-H-8083-3)

The gear warning horn will sound when the airplane is configured for landing and the landing gear is not down and locked. Normally, the horn is linked to the throttle or flap position, and/or the airspeed indicator so that when the airplane is below a certain airspeed, configuration, or power setting with the gear retracted, the warning horn will sound.

6. How is inadvertent gear retraction on the ground prevented? (FAA-H-8083-3)

Accidental retraction of the landing gear may be prevented by such devices as mechanical downlocks, safety switches, and ground locks. Mechanical downlocks are built-in components of a gear retraction system and are operated automatically. To prevent accidental operation of the downlocks and inadvertent landing gear retraction while the airplane is on the ground, electrically operated safety switches are installed.

7. Explain how a landing gear safety switch (squat switch) operates. (FAA-H-8083-3)

A landing gear safety switch, sometimes referred to as a squat switch, is usually mounted in a bracket on one of the main gear shock struts. When the strut is compressed by the weight of the airplane, the switch opens the electrical circuit to the motor or mechanism that powers retraction. In this way, if the landing gear switch in the

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