Frost & ice formation on the ground
Surface ice types:
| Type | Description | Cite |
|---|---|---|
| Hoarfrost | Uniform thin white deposit of fine crystals on exposed surfaces; calm, cloudless, below-freezing nights; no precipitation; paint lines show through | TP 10643 para 17 |
| Clear ice | Glossy, clear or translucent; hard to see; forms on cold-soaked wing areas above fuel tanks | TC AIM MET Table 2.4; TC AIM AIR 2.12.2 |
| Slush | Mix of frozen and liquid water | TP 10643 glossary |
| Wet snow | Near 0 degrees C: very critical for clear ice | TC AIM AIR 2.12.2 |
Hoarfrost formation (PHAK ch.12):
- Needs calm air and surface air near saturation.
- Same cooling as dew: clear, calm night lets ground chill surface air below dew point.
- Moisture deposits as dew above freezing, frost below.
Cold-soaked fuel (TC AIM AIR 2.12.2):
- Frosts upper wing even when OAT above freezing: fuel chilled at altitude keeps wing skin below 0 degrees C after landing.
- Fuel temperature can drop as much as 18 degrees C over a two-hour flight.
- Abnormally large amount of cold fuel left in tanks can contact upper wing panels, especially at wing root: feeds clear ice there.
- Wet snow, drizzle, or rain near 0 degrees C: very critical for clear ice. Heavy freezing reported in drizzle or rain between +8 and +14 degrees C.
- Frost over fuel tank region during turnaround re-forms quickly even after removal.
Trap: above-freezing OAT does not rule out frost; cold-soaked fuel forms it on wing.
References
- TC AIM AIR 2.12.2
- TC AIM MET Table 2.4
- TP 10643 (When in Doubt... Small and Large Aircraft)
- PHAK ch.12 (Dew and Frost)