Definition
The altitude at which the air temperature first reaches 0 °C (32 °F) as you climb through the atmosphere. On a Multi-Function Display, freezing level data is typically shown as contour lines or shaded layers indicating the height of the 0 °C isotherm across a region, and may also show the heights of additional freezing layers when temperature inversions create more than one.
Plain English
The height in the sky where the air becomes cold enough for water to freeze. Below it, the air is above freezing; above it, the air is at or below freezing.
Context Anchor
Seen on cockpit weather displays, weather briefings, and preflight planning tools when checking possible icing conditions along a route.
Derivation
‘Freezing level’ is plain English, but pilots should note it refers to a height (an altitude in feet MSL), not a temperature or a place on the ground. The ‘level’ is the altitude where the freezing condition begins.
Why Pilots Care
It shows where icing conditions may begin, helping pilots choose safer altitudes and routes.
Grounding Statement
Picture a horizontal line drawn through the sky at the altitude where the thermometer reads 0 °C — that line is the freezing level.
Intuition Check
Do not assume a freezing level means ice is present everywhere at that altitude. It only tells you the temperature is cold enough for freezing; moisture is also needed for ice to form on the airplane.
Example Sentence 1
The MFD showed the freezing level at 6,000 feet, so she planned to cruise at 4,500 to stay below it and out of the clouds where icing was likely.
Example Sentence 2
Climbing through the freezing level in visible moisture required immediate activation of the anti-ice systems.