FAA Aviation Mechanic Airframe (AMA)Fuel, Cabin and Ice Control SystemsHard
A technician is troubleshooting a vibrating rod-type ice detector on a turbine aircraft that is giving false ice indications. What operating principle explains how this sensor normally detects ice accumulation?
- AIt uses a photoelectric cell to detect ice reflecting light onto a sensor
- BIt detects a change in electrical resistance across a heated wire grid
- CIt measures a decrease in the natural vibration frequency of a probe as ice mass builds up on it
- DIt measures airflow blockage across a venturi caused by ice buildup
Show answer & explanationAnswer & explanation
Correct answer: C. It measures a decrease in the natural vibration frequency of a probe as ice mass builds up on it
A vibrating rod ice detector oscillates a small probe at a natural resonant frequency; as ice accumulates on the probe, added mass lowers the resonant frequency, which the system senses and uses to trigger an ice warning or automatically actuate deicing.
Why the other options are wrong
- A. Photoelectric detection is not used in standard vibrating rod ice detector systems.
- B. Resistance-grid detection describes a different (electrothermal) ice detection method, not vibrating rod sensors.
- D. Venturi airflow blockage is not the operating principle of vibrating rod detectors.
Vibrating Rod Ice Detector
An ice detection sensor that vibrates a small probe at a known resonant frequency; ice accumulation adds mass that lowers the frequency, which the system interprets as ice buildup.
- Common on turbine and helicopter ice protection systems
- Frequency decrease is proportional to accumulated ice thickness
- Often self-deices periodically by internal heating to reset baseline
Memory trick: Ice adds weight, slowing the rod's vibrating hum.