FAA Ground School Practice Test

How do variations in temperature affect the altimeter?

1. Indicated altitude is higher than true altitude on cold days

2. Pressure levels are raised on warm days

3. Indicated altitude becomes less accurate in cloudy weather

4. Indicated altitude is lower than true altitude on warm days

The correct answer is: Indicated altitude is lower than true altitude on warm days

Variations in temperature significantly impact the altimeter's readings due to the way it measures atmospheric pressure changes. The altimeter operates based on the Standard Atmosphere model, which assumes specific temperature and pressure values at different altitudes. In this model, as temperature increases, the atmosphere expands, leading to a decrease in air density. On warm days, the lower density of warm air means that the same pressure level is found at a higher altitude compared to cooler air. Consequently, if a pilot is using an altimeter calibrated to the standard temperature, it will indicate an altitude that is actually lower than the true altitude. Therefore, when flying in warmer temperatures, if the altimeter setting is not adjusted to account for the temperature variation, the indicated altitude may be misleading, leading pilots to inaccurately perceive their actual height above the ground. Understanding this relationship between temperature and altimeter readings is crucial for pilots to ensure safe altitude management during flight.