Free Airframe Mechanic Aircraft Landing Gear Systems Questions and Answers — Questions and Answers
Question 1: A technician observes paint lines on an aircraft's tire and wheel rim that are no longer aligned. What is the primary purpose of these 'creep marks'?
- To indicate the correct valve stem position for tube alignment.
- To show if the tire has slipped on the wheel rim. (Correct answer)
- To provide a visual reference for tire tread wear.
- To mark the proper location for attaching wheel balance weights.
Correct answer: To show if the tire has slipped on the wheel rim.
Creep marks, or slippage marks, are painted lines that extend from the wheel rim to the tire sidewall. Their purpose is to provide a visual indication of whether the tire has rotated or 'slipped' on the wheel rim. This is especially critical for tubed tires, as significant slippage can shear the valve stem off the inner tube, leading to a rapid loss of tire pressure.
Question 2: What is the primary function of a centering cam in a retractable nose landing gear system?
- To dampen nose wheel shimmy during taxi operations.
- To engage the nose wheel steering system after landing.
- To align the nose wheel in the fore-and-aft direction before retraction. (Correct answer)
- To absorb landing shock forces through the shock strut.
Correct answer: To align the nose wheel in the fore-and-aft direction before retraction.
A centering cam is a mechanical device within the nose gear shock strut that ensures the nose wheel is aligned straight (fore-and-aft) before it is retracted into the wheel well. As the strut extends fully after takeoff (when the aircraft's weight is off the wheels), two cams, one upper and one lower, engage to lock the wheel in the centered position, preventing damage to the aircraft structure during retraction.
Question 3: During a ground maintenance check on a retractable-gear aircraft, a technician attempts to raise the landing gear using the cockpit selector switch, but the gear does not retract. Which safety device is most likely preventing the gear retraction?
- The downlock mechanism.
- The gear-up indicator light.
- The hydraulic bypass valve.
- The squat switch (or weight-on-wheels switch). (Correct answer)
Correct answer: The squat switch (or weight-on-wheels switch).
A squat switch, also known as a weight-on-wheels switch, is a safety device that prevents accidental retraction of the landing gear when the aircraft is on the ground. It senses when the aircraft's weight is compressing the landing gear struts and opens an electrical circuit to the retraction mechanism, making it impossible to raise the gear.
Question 4: A pilot reports a violent, uncontrolled, side-to-side oscillation of the nose wheel during takeoff and landing rolls. Which of the following conditions is the most likely cause?
- An over-inflated nose wheel tire.
- Nose wheel shimmy. (Correct answer)
- Hydraulic fluid cavitation in the brake lines.
- A malfunctioning centering cam.
Correct answer: Nose wheel shimmy.
The condition described is a classic symptom of nose wheel shimmy. This is a rapid, uncontrolled side-to-side oscillation that can be caused by several factors, including worn torque link bushings, an improperly serviced or failing shimmy damper, incorrect tire pressure, or an out-of-balance wheel/tire assembly.
Question 5: When performing a landing gear retraction test, the aircraft should be placed on jacks in a specific configuration. What is a critical reason for this procedure?
- To allow for easier access to the brake system for inspection.
- To simulate the air loads that the gear experiences in flight.
- To ensure the squat switches are in the 'in-flight' or 'unloaded' position. (Correct answer)
- To reduce the hydraulic pressure required to cycle the gear.
Correct answer: To ensure the squat switches are in the 'in-flight' or 'unloaded' position.
Placing an aircraft on jacks allows the landing gear struts to fully extend, releasing the compression on the squat switches (weight-on-wheels switches). This moves the switches into their 'in-flight' configuration, which closes the electrical circuit and allows the landing gear retraction system to be operated from the cockpit for testing purposes.
Question 6: A technician inspecting a multi-disc brake system notices that one of the brakes is dragging after pressure is released. Which of the following is a plausible cause for this issue?
- The use of nitrogen instead of compressed air to service the tire.
- Excessive wear on the brake disc's anti-skid sensor.
- A weak or broken return spring in the brake assembly. (Correct answer)
- Creep marks on the tire are misaligned by more than one inch.
Correct answer: A weak or broken return spring in the brake assembly.
Brake drag occurs when the brake pads do not fully retract from the rotor after braking pressure is released. A weak or broken return spring within the brake caliper or piston housing is a common cause, as it fails to provide the necessary force to pull the pistons and pads away from the disc. Other causes can include a jammed piston, contaminated hydraulic fluid, or a malfunctioning master cylinder.
Free Airframe Mechanic Aircraft Landing Gear Systems Questions and Answers
A technician observes paint lines on an aircraft's tire and wheel rim that are no longer aligned.
What is the primary purpose of these 'creep marks'?