Private Pilot Private Exam

If the altimeter setting is increased from 29.15 to 29.85, what happens to the indicated altitude?

1. The indicated altitude decreases by 700 feet

2. The indicated altitude increases by 700 feet

3. The indicated altitude remains unchanged

4. The altimeter cannot be adjusted safely

The correct answer is: The indicated altitude increases by 700 feet

When the altimeter setting is increased from 29.15 to 29.85, the indicated altitude will increase, which means the aircraft's altitude reading will show a higher elevation than before. This change occurs because the altimeter measures the atmospheric pressure and uses it to determine the altitude. When the altimeter setting is lower (in this case, 29.15 inches of mercury), it means that the actual air pressure at sea level is higher than the pressure that the altimeter is set to measure. Adjusting the altimeter to a higher setting means it is now calibrated to a higher sea level pressure, indicating that the aircraft is at a higher altitude than what was previously displayed at the lower setting. The difference in pressure translates to a specific change in indicated altitude—approximately 700 feet for a 0.70 inch of mercury increase in pressure. This scenario illustrates the importance of correctly setting the altimeter to ensure accurate altitude readings, particularly during approaches and landings where precise altitude information is critical.