Airframe Mechanic Certification Ice and Rain Control Systems 3 — Questions and Answers
Question 1: Electrothermal ice protection systems on helicopter rotor blades typically use which power source?
- Engine bleed air converted to electricity
- Dedicated 400 Hz AC generators (Correct answer)
- 28V DC from the main battery only
- Ground power unit only during preflight
Correct answer: Dedicated 400 Hz AC generators
Helicopter rotor blade heaters typically use 400 Hz AC power from dedicated generators to handle the high power demands of blade deicing.
Question 2: What is 'runback ice' and why is it a concern?
- Ice that forms at the base of the vertical stabilizer from fuel venting
- Water melted by the anti-ice system that refreezes further aft on an unheated surface (Correct answer)
- Condensation that runs back from the cockpit windows
- Ice shed from the propeller that strikes the fuselage
Correct answer: Water melted by the anti-ice system that refreezes further aft on an unheated surface
Runback ice forms when melted water from a heated zone flows aft and refreezes on an unprotected surface, potentially creating a dangerous ridge.
Question 3: Which component in a hot air wing anti-icing system regulates the temperature of bleed air delivered to the leading edge?
- Flow control and shutoff valve
- Precooler or mixing valve (Correct answer)
- Turbine inlet temperature sensor
- Crossfeed manifold check valve
Correct answer: Precooler or mixing valve
A precooler or mixing valve blends hot bleed air with cooler air (or ambient) to maintain the leading edge at an effective but safe temperature.
Question 4: During a ground run-up, at what condition should wing thermal anti-ice normally NOT be operated for extended periods?
- At idle power settings below 40°F OAT
- At high power settings with no airflow over the wings (Correct answer)
- Whenever outside air temperature is above 50°F
- During any ground operation regardless of conditions
Correct answer: At high power settings with no airflow over the wings
Without airflow to cool the leading edge skins, extended ground operation of wing thermal anti-ice can cause overheating and structural damage.
Question 5: What is the primary reason windshield anti-icing systems use a thin conductive coating or embedded resistance wires rather than bleed air?
- Bleed air systems cannot reach high enough temperatures for windshield deicing
- Bleed air would cause pressure differential failures in the windshield sandwich
- Electrical systems provide uniform, controllable heating without disturbing vision (Correct answer)
- Regulations prohibit bleed air contact with transparency materials
Correct answer: Electrical systems provide uniform, controllable heating without disturbing vision
Electrical heating elements provide precise, even temperature distribution across the windshield without the optical distortion that hot air impingement could create.
Question 6: A propeller electric deicing system shows uneven heating between blades. Which component is most likely at fault?
- The slip ring and brush block assembly (Correct answer)
- The main circuit breaker for the deicing bus
- The flight deck control switch
- The aircraft's main generator
Correct answer: The slip ring and brush block assembly
The slip ring and brush assembly transfers electrical power from the stationary airframe to the rotating propeller; worn brushes or a dirty slip ring cause uneven or intermittent power delivery.
Question 7: Which meteorological condition is most likely to produce clear (glaze) ice on an airframe?
- Light snow at temperatures below -20°C
- Freezing drizzle with large supercooled water droplets just below 0°C (Correct answer)
- Dry snow with OAT around -5°C
- Moderate turbulence inside a towering cumulus
Correct answer: Freezing drizzle with large supercooled water droplets just below 0°C
Freezing drizzle contains large supercooled droplets that spread and freeze slowly on impact, forming a clear, dense glaze ice layer.
Airframe Mechanic Certification Ice and Rain Control Systems 3
Electrothermal ice protection systems on helicopter rotor blades typically use which power source?