FAA Ground School Practice Test

If a flight is made from an area of low pressure into an area of high pressure without adjusting the altimeter setting, what will the altimeter indicate?

1. Higher than the actual altitude above sea level

2. Lower than the actual altitude above sea level

3. The same as the actual altitude

4. An incorrect value

The correct answer is: Lower than the actual altitude above sea level

When flying from a low-pressure area to a high-pressure area without adjusting the altimeter setting, the altimeter will indicate a lower altitude than the actual altitude above sea level. The altimeter measures the atmospheric pressure and translates that into altitude, typically based on a standard atmosphere at sea level. In a low-pressure area, the actual altitude is higher for a given pressure reading on the altimeter. When transitioning to a high-pressure area, the atmospheric pressure increases, meaning that the altitude given by the unadjusted altimeter will read lower, as it was calibrated for lower pressure conditions. Therefore, the aircraft would be at a greater altitude than what the altimeter indicates, leading to the reading being lower than the actual altitude above sea level in a high-pressure environment. This scenario highlights the importance of adjusting the altimeter setting according to local atmospheric pressure to ensure accurate altitude readings.