Airframe Mechanic Ice and Rain Control Systems Questions and Answers — Questions and Answers
Question 1: A turbine-powered aircraft's thermal anti-icing system for the wing leading edges is indicating a fault. The system uses engine bleed air. Which of the following is the most likely cause for the system to fail to operate correctly?
- The pneumatic de-icing boots are operating simultaneously.
- The chemical rain repellent system reservoir is empty.
- The anti-ice valve has failed to open. (Correct answer)
- The windshield wiper motor has shorted out.
Correct answer: The anti-ice valve has failed to open.
Thermal anti-icing systems on turbine aircraft typically use hot bleed air from the engine's compressor section. This hot air is ducted to the leading edges of the wings and tail surfaces. A critical component in this system is the anti-ice valve, which controls the flow of bleed air. If this valve fails to open, hot air cannot reach the leading edges, rendering the system inoperative and triggering a fault indication.
Question 2: When inspecting a pneumatic de-icing boot, which condition would most likely require replacement of the boot rather than a repair?
- Minor surface cracking due to ozone exposure.
- A small, clean puncture away from the edges.
- Mild abrasions from dust and debris.
- Damage that exposes the underlying stitch-line threads. (Correct answer)
Correct answer: Damage that exposes the underlying stitch-line threads.
While minor cracks, abrasions, and some punctures can often be repaired according to the manufacturer's instructions, damage that is severe enough to expose the internal stitch-line threads compromises the structural integrity of the boot. Such damage can lead to catastrophic failure of the boot during inflation and requires replacement.
Question 3: What is the primary principle of operation for chemical rain repellent systems on an aircraft windshield?
- It heats the windshield to evaporate rain on contact.
- It creates a super-slick surface that prevents water from adhering, causing it to bead up and be blown away. (Correct answer)
- It uses high-velocity air to blast rain from the windshield surface.
- It mixes with rainwater to lower its freezing point.
Correct answer: It creates a super-slick surface that prevents water from adhering, causing it to bead up and be blown away.
Chemical rain repellent works by applying a chemical film to the windshield. This film creates a hydrophobic surface, which significantly reduces the adhesion of water. As a result, raindrops that hit the windshield draw up into beads instead of spreading out, allowing the aerodynamic forces of the slipstream to easily blow them away, improving visibility.
Question 4: During an operational check of an electric windshield wiper system, the wipers operate correctly at both high and low speeds but fail to return to the 'park' position when the switch is turned off. Which component is most likely malfunctioning?
- The wiper motor.
- The wiper arm.
- The park switch or associated circuit. (Correct answer)
- The main power supply relay.
Correct answer: The park switch or associated circuit.
Aircraft windshield wiper systems have a mechanism to automatically return the blades to a parked position, out of the pilot's line of sight, when turned off. This is controlled by a dedicated park switch or a specific part of the control circuit. If the motor runs at normal speeds but fails to park, it indicates that the main motor is functional, but the circuit that should keep the motor running just until the blades are parked is faulty.
Question 5: Which of the following is a critical maintenance practice for pneumatic de-icing boots to ensure their longevity and proper function?
- Keeping the boots inflated when the aircraft is parked to prevent creasing.
- Applying a thin layer of hydraulic fluid to keep the rubber supple.
- Regularly cleaning the boots with soap and water and performing visual inspections. (Correct answer)
- Testing the system exclusively in sub-zero temperatures to simulate real-world conditions.
Correct answer: Regularly cleaning the boots with soap and water and performing visual inspections.
Proper care for pneumatic de-icing boots includes regular cleaning with approved mild soap and water to remove insects and contaminants that can degrade the rubber. This is followed by a thorough visual inspection for damage such as cracks, cuts, abrasions, or signs of delamination. This routine maintenance is crucial for identifying issues early and extending the service life of the boots.
Question 6: An aircraft's wing anti-ice system uses hot air. In most large, turbine-powered aircraft, what is the source of this hot air?
- Exhaust from the auxiliary power unit (APU).
- Electric heating elements embedded in the wing's leading edge.
- Ram air heated by passing over the engine exhaust nacelle.
- Bleed air from the engine's compressor section. (Correct answer)
Correct answer: Bleed air from the engine's compressor section.
The most common method for providing heat to wing and tail anti-icing systems on turbine-powered aircraft is by using hot air bled from the compressor section of the engines. This high-temperature, high-pressure air is a readily available source of thermal energy, which is then ducted to the leading edges to prevent ice formation.
Airframe Mechanic Ice and Rain Control Systems Questions and Answers
A turbine-powered aircraft's thermal anti-icing system for the wing leading edges is indicating a fault.
The system uses engine bleed air.
Which of the following is the most likely cause for the system to fail to operate correctly?