If a pilot changes the altimeter setting from 30.11 in Hg to 29.96 in Hg, how much lower will the altimeter indicate?

When altering the altimeter setting, it is essential to understand that a decrease in the altimeter setting will result in the altimeter indicating a lower altitude. This is based on the principle that the altimeter is calibrated to the standard atmospheric pressure at sea level, and any deviation from this standard requires adjustment.

In this scenario, the pilot changes the altimeter setting from 30.11 inches of mercury to 29.96 inches of mercury. The difference between these two settings is 0.15 inches of mercury. Since an altimeter is generally calibrated such that every 0.01 inches of mercury corresponds to about 28 feet of elevation change, we can calculate the altitude change resulting from a 0.15 inches change in the altimeter setting.

The calculation is straightforward: you multiply the change in inches (0.15 inches) by the corresponding feet per inch factor (28 feet). Hence, 0.15 inches multiplied by 28 feet gives: 0.15 x 28 = 4.2 feet.

However, to find the total change in altitude indicated by the altimeter, we multiply the total change in pressure (0.15 inches) by 100, leading to 15 feet lower for each hundredths.