Airframe Mechanic Certification Ice and Rain Control Systems 4 — Questions and Answers
Question 1: What is the purpose of the piccolo tube (spray tube) in a thermal anti-icing leading edge system?
- To direct hot bleed air through small holes against the inside of the leading edge skin (Correct answer)
- To spray deicing fluid onto the external wing surface
- To distribute electrical heating current along the leading edge spar
- To vent excess bleed air overboard through the leading edge
Correct answer: To direct hot bleed air through small holes against the inside of the leading edge skin
The piccolo tube has small holes that direct jets of hot bleed air against the inner surface of the leading edge skin for uniform heating.
Question 2: Rain repellent systems that use a chemical compound on windshields work on which principle?
- Warming the glass surface so water evaporates before accumulating
- Creating a hydrophobic surface that causes water to bead and blow off (Correct answer)
- A chemical reaction that bonds water molecules to the glass permanently
- Ionizing the water droplets to repel them electrostatically
Correct answer: Creating a hydrophobic surface that causes water to bead and blow off
Rain repellent compounds create a hydrophobic coating that causes water to bead into droplets that are removed by airflow.
Question 3: What is the maximum allowable time a deicing boot should remain inflated in a typical inflation/deflation cycle?
- Continuously inflated whenever icing conditions exist
- Approximately 6–8 seconds inflation followed by deflation and suction hold-down (Correct answer)
- 30 seconds on, 30 seconds off automatically
- Until the pilot deflates it manually after each ice shed cycle
Correct answer: Approximately 6–8 seconds inflation followed by deflation and suction hold-down
Typical boot cycles inflate for about 6–8 seconds to crack and shed ice, then deflate with suction applied to hold the boot flat and reduce aerodynamic drag.
Question 4: When is it appropriate to activate pneumatic deicing boots according to standard operating procedures?
- Immediately upon entering any visible moisture below 10°C
- After a sufficient accumulation of ice (typically 1/4 to 1/2 inch) has formed (Correct answer)
- Only during ground operations before takeoff in icing conditions
- As soon as the ice detection system illuminates its first advisory light
Correct answer: After a sufficient accumulation of ice (typically 1/4 to 1/2 inch) has formed
Manufacturers typically recommend allowing a minimum ice build-up before cycling boots so the ice layer is thick enough to be broken and shed effectively.
Question 5: Which material is commonly used for the outer surface of pneumatic deicing boots because of its resistance to abrasion and ozone?
- Silicone rubber
- Natural latex rubber
- Neoprene rubber (Correct answer)
- Butyl rubber
Correct answer: Neoprene rubber
Neoprene (polychloroprene) rubber is widely used for deicing boot outer surfaces due to its good resistance to abrasion, ozone, weathering, and aviation fluids.
Question 6: What type of ice protection does the engine air inlet of most large turbofan engines rely upon?
- Pneumatic expansion boots on the inlet lip
- Electrothermal heating mats bonded to the inlet lip
- Hot bleed air from an engine stage ducted through the inlet lip (Correct answer)
- Chemical fluid sprayed from a nozzle inside the nacelle
Correct answer: Hot bleed air from an engine stage ducted through the inlet lip
Turbofan engine inlets use hot bleed air ducted through the inlet lip structure to prevent ice formation and protect engine internals.
Question 7: The term 'SLD' in the context of icing regulations refers to which hazardous icing condition?
- Severe Low-level Downdraft
- Supercooled Large Droplets (Correct answer)
- Sustained Low-temperature Drizzle
- Structural Limit Deformation
Correct answer: Supercooled Large Droplets
Supercooled Large Droplets (SLD) are a particularly hazardous icing condition because their size allows them to impact areas aft of typical ice protection coverage.
Airframe Mechanic Certification Ice and Rain Control Systems 4
What is the purpose of the piccolo tube (spray tube) in a thermal anti-icing leading edge system?