Private Pilot Private Exam

What is the expected behavior of the altimeter when flying from high pressure to low pressure without adjustment?

1. It indicates lower altitude than true altitude

2. It indicates the correct altitude

3. It indicates higher altitude than true altitude

4. It provides erratic readings

The correct answer is: It indicates higher altitude than true altitude

When flying from an area of high pressure to an area of low pressure without adjusting the altimeter setting, the altimeter will indicate a higher altitude than the true altitude. This occurs because the altimeter is calibrated to the pressure of the air at sea level, which is typically set to 29.92 inches of mercury (Hg) or 1013.25 hPa. When you move to lower pressure areas without recalibrating, the altimeter continues to reference the higher pressure setting it was previously set to. As a result, the decrease in air pressure associated with lower altitudes goes unaccounted for, causing the altimeter to read higher than the actual altitude above sea level. This discrepancy can lead pilots to believe they are flying at a higher altitude than they truly are, which is particularly critical when navigating in mountainous or varying terrain. Properly adjusting the altimeter to the local atmospheric pressure is essential for accurate altitude readings and safe flight operations.