Density Altitude
Pressure altitude corrected for temperature.
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Example
Hot air reduces performance
How it works
Density altitude is the altitude in the standard atmosphere that would have the same air density as the air at your current location. It combines the effect of pressure altitude and temperature, because warm air is less dense and behaves as if the aircraft were operating higher up. The "120" factor is an aviation approximation that converts a temperature difference in °C into an equivalent altitude change in feet.
When to use it
Use this when estimating aircraft performance for takeoff, climb, and landing, especially on hot days or at high-elevation airports. It is also useful in flight planning, weight-and-balance decisions, and understanding why an aircraft may underperform even when the field elevation looks acceptable.
Worked example, step by step
Given: PA = 4,500 ft OAT = 32°C ISA at 4,500 ft ≈ 15 - (2 × 4.5) = 6°C Step 1: Find the temperature difference OAT - ISA = 32 - 6 = 26°C Step 2: Convert temperature difference to altitude correction 120 × 26 = 3,120 ft Step 3: Add to pressure altitude DA = PA + 120(OAT - ISA) DA = 4,500 + 3,120 DA = 7,620 ft Final answer: Density altitude = 7,620 ft
Common mistakes to avoid
- Using airport elevation instead of pressure altitude
- Forgetting to calculate ISA temperature for the actual pressure altitude
- Mixing Celsius and Fahrenheit, which makes the 120 factor invalid
Did You Know?
On a hot day at a high airport, density altitude soars and aircraft struggle to generate lift.
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