1. What is ISA Deviation?

ISA (International Standard Atmosphere) Deviation is the difference between the observed outside air temperature (OAT) and the standard temperature at a given altitude according to the ISA model. It's a crucial parameter in aviation for aircraft performance calculations.

2. How Does the Calculator Work?

The calculator uses the ISA Deviation formula:

Where:

• \( Dev \) — ISA Deviation (°C)
• \( OAT \) — Observed Air Temperature (°C)
• \( ISA \) — Standard Temperature at given altitude (°C)

Explanation: A positive deviation indicates temperatures warmer than standard, while a negative deviation indicates temperatures colder than standard.

3. Importance of ISA Deviation Calculation

Details: ISA deviation is critical for aircraft performance calculations including takeoff distance, climb performance, engine power output, and fuel consumption. It helps pilots and flight planners make accurate performance predictions.

4. Using the Calculator

Tips: Enter both OAT and ISA temperatures in degrees Celsius. The calculator will compute the difference between these values to determine the ISA deviation.

5. Frequently Asked Questions (FAQ)

Q1: What is the standard ISA temperature at sea level?
A: The standard ISA temperature at sea level is 15°C (59°F).

Q2: How does altitude affect ISA temperature?
A: In the standard atmosphere, temperature decreases by approximately 1.98°C per 1,000 feet (or 6.5°C per 1,000 meters) of altitude gain.

Q3: Why is ISA deviation important for aircraft performance?
A: Warmer than standard temperatures reduce air density, which decreases aircraft performance (longer takeoff distance, reduced climb rate). Colder temperatures have the opposite effect.

Q4: How is ISA temperature calculated at different altitudes?
A: ISA temperature at a given altitude = 15°C - (altitude in feet × 1.98°C/1000ft) or = 15°C - (altitude in meters × 6.5°C/1000m).

Q5: Does ISA deviation affect fuel consumption?
A: Yes, in warmer conditions (positive deviation), aircraft may consume more fuel due to reduced efficiency, while in colder conditions (negative deviation), fuel consumption may be slightly reduced.