Airframe Mechanic Certification Ice and Rain Control Systems 2 — Questions and Answers
Question 1: What is the primary purpose of a pneumatic deicing boot on an aircraft?
- To prevent ice from forming by heating the leading edge
- To inflate and break off ice that has accumulated on the leading edge (Correct answer)
- To spray deicing fluid onto the wing surface
- To redirect bleed air over the wing to melt ice
Correct answer: To inflate and break off ice that has accumulated on the leading edge
Pneumatic deicing boots inflate cyclically to fracture and shed ice that has already formed on the leading edge.
Question 2: Which FAR part establishes the certification standards for ice protection systems on transport category aircraft?
- FAR Part 23
- FAR Part 25 (Correct answer)
- FAR Part 27
- FAR Part 91
Correct answer: FAR Part 25
FAR Part 25 covers airworthiness standards for transport category airplanes, including ice protection requirements.
Question 3: On a pneumatic deicing system, what controls the inflation sequence of the boots?
- The ice detector sensor directly
- A timer or distributor valve (Correct answer)
- Bleed air pressure alone
- The flight crew manually inflating each boot
Correct answer: A timer or distributor valve
A timer or distributor valve sequences the inflation of individual boot sections in a predetermined order.
Question 4: What type of fluid is used in a TKS (weeping wing) ice protection system?
- Isopropyl alcohol
- Ethylene glycol-based fluid (Correct answer)
- Hydraulic fluid MIL-H-5606
- Methanol mixed with water
Correct answer: Ethylene glycol-based fluid
TKS systems use an ethylene glycol-based fluid (MEG or similar) that lowers the freezing point of water on the surface.
Question 5: An ice detector that uses a vibrating probe operates on which principle?
- Changes in electrical resistance as ice builds up
- Changes in the resonant frequency of the probe as ice accretes (Correct answer)
- Optical scattering of light by ice crystals
- Temperature differential between probe and ambient air
Correct answer: Changes in the resonant frequency of the probe as ice accretes
Vibrating-probe ice detectors sense ice accumulation by detecting the change in resonant frequency caused by added mass on the probe.
Question 6: When inspecting a pneumatic deicing boot, a mechanic finds a small blister between the boot and the leading edge skin. What is the correct action?
- Inject cement into the blister and clamp until cured
- Deflate the boot and continue if blister is under 1 inch
- Replace the boot if delamination exceeds allowable limits per the SRM (Correct answer)
- Sand the blister flat and apply surface tape
Correct answer: Replace the boot if delamination exceeds allowable limits per the SRM
Blister size limits and acceptable repairs are defined in the Structural Repair Manual; delamination beyond limits requires boot replacement.
Question 7: What is the function of the check valve in a pneumatic deicing boot system?
- To limit maximum inflation pressure to 20 psi
- To prevent backflow of air that could collapse an inflated boot prematurely (Correct answer)
- To allow the pilot to manually override automatic sequencing
- To filter moisture from the bleed air supply
Correct answer: To prevent backflow of air that could collapse an inflated boot prematurely
Check valves prevent reverse airflow through the system, ensuring each boot section holds pressure during its inflation cycle.
