Hazards from windshield ice
Windshield icing is caused by:
- Outside — precipitation freezing on a cold pane,
- Inside — cabin air condensing on the cold pane (fogging in humid conditions, ice in very cold outside air),
- Frost when parked overnight (radiation frost).
Effects on the pilot:
- Loss of vision: Heavy ice or fog blocks visual flight — required visibility minima cannot be met.
- Approach/landing: loss of runway, lights and threshold marking visibility — highest CFIT risk.
- Traffic lookout: Other aircraft become invisible → collision risk.
Windshield de-icing systems in PPL aircraft
Most training aircraft (C172, PA-28, DA40) have no dedicated heated windshield as found in airliners — instead typically:
1. Cabin heat with defroster vents
- Hot air from the heater muff (around the exhaust manifold) is routed through defroster ducts onto the windshield.
- Works inside against fogging and light icing.
- Outside ice is removed only slowly by interior heat.
2. Manual wiping
- Some aircraft have a mechanical windshield wiper.
- Ineffective against ice; limited use in rain.
3. Larger GA and IFR aircraft — glycol spray system
- TKS fluid (glycol mixture) is sprayed onto the windshield through small nozzles.
- Works in both anti-icing and de-icing modes.
- Limited supply (typically 5–10 litres, good for 30–60 min in moderate icing).
4. Airliners — electrically heated windshield
- Pane consists of several layers with embedded wire mesh or conductive film.
- Electrically heated; anti-icing and bird-strike protection.
Operational recommendations
Before flight with frost on ground:
- Never take off with frost/ice on the windshield, simply by the clean-aircraft principle.
- Remove ice mechanically (carefully on the outside; Plexiglas is soft — do not scratch),
- Activate cabin heat with defroster early.
In flight:
- Inside fog → heat + defroster on max, possibly fresh-air vents.
- Outside icing → leave icing conditions immediately (climb to warmer air, descend, turn back).
- Consider emergency landing if visibility is severely impaired.
Plexiglas-specific notes
Most PPL windows are made of Plexiglas (PMMA), not glass:
- Sensitive to solvents — no acetone, methanol, alcohol, glass cleaners with ammonia!
- Use specific Plexiglas cleaners or clean water with a soft cloth.
- Scratch-sensitive: no metal ice scrapers, no stiff brushes — only soft plastic scrapers.