Overview
This lesson explains how ice forms on aircraft during flight, the danger it presents, and the main systems used to detect and warn pilots about in-flight icing conditions.
How Ice Forms on Aircraft
- Icing occurs when supercooled water droplets freeze on forward-facing surfaces of aircraft in flight.
- Supercooled droplets exist between 0°C and -40°C; below -40°C, droplets are already frozen and will not adhere.
- Ice buildup can seriously affect aircraft aerodynamics and safety.
- Icing is a risk whenever both low temperatures (0°C to -40°C) and visible moisture (cloud or rain) are present.
Types of Ice Detection Systems
- There are two main ice detection system types: accretion (detect actual ice buildup) and inferential (detect environmental icing conditions).
- The simplest accretion detector is visual: the pilot monitors visible surfaces for ice.
- Many aircraft have lights to help pilots see ice buildup at night.
Accretion Type Ice Detectors
- Teddington Ice Detector: Mast visible from cockpit, ice visibly builds up and can be melted by a heater.
- Smiths Ice Detector: Tube with pressure-sensitive capsule; ice blocks holes, lowers pressure, and triggers warning light.
- English Electric/Napier Detector: Rotor shaft shaves off ice; increased torque triggers a microswitch warning.
- Rosemount Ice Detector: Vibrating probe; ice reduces vibration frequency, triggering a warning and activating a de-icing heater.
- Beta Particle Detector: Uses beta particles; ice absorbs particles, and reduced detection triggers a warning at a set ice thickness.
Inferential Type Ice Detectors
- Sangamo Weston Ice Detector: Detects icing conditions by measuring both moisture and freezing temperature; issues warning if both are present.
- Inferential detectors trigger warnings or automatic anti-icing cycles when icing conditions are identified.
Key Terms & Definitions
- Supercooled water droplets — Liquid water below 0°C but not yet frozen, main cause of in-flight icing.
- Accretion type detector — Detects actual ice buildup on the aircraft.
- Inferential type detector — Senses environmental conditions (moisture and temperature) that could produce icing.
- Beta particle detector — Uses radioactive particles to detect ice by the amount absorbed by ice accumulation.
Action Items / Next Steps
- Review the types and operation of ice detection systems.
- Be able to identify conditions when in-flight icing is likely to occur.
- Ensure understanding of where pilots can first spot ice buildup on an aircraft.