Private Pilot Private Exam

Under which circumstance will true altitude be lower than the indicated altitude?

1. Warm air temperature

2. Colder than standard air temperature

3. Normal air pressure

4. Increased humidity

The correct answer is: Warm air temperature

True altitude refers to the actual height of an aircraft above sea level, while indicated altitude is what the altimeter reads based on the current local atmospheric pressure setting. When the air temperature is warmer than standard conditions, the density of the air becomes less than it would be at standard temperature. Since the altimeter is calibrated to measure height based on standard atmospheric conditions, it relies on the standard pressure and temperature values. In warm air, the actual altitude (true altitude) of the aircraft is less than what the altimeter indicates (indicated altitude). The altimeter interprets the lower density of the warm air as the aircraft being at a higher altitude than it actually is. Therefore, in situations where the air temperature is warmer than standard, true altitude will be lower than the indicated altitude. Understanding the relationship between temperature, pressure, and altitude readings is essential for pilots to ensure accurate navigation and safe flight operations.