If my altimeter is set to 30.10 in Hg and the MSL pressure is actually 29.80 in Hg, my actual altitude is:

• A. 300 ft higher
• B. 300 ft lower
• C. 10 ft lower
• D. 10 ft higher

Answer: (B)

To determine the actual altitude when the altimeter setting differs from the mean sea level (MSL) pressure, one can use the pressure altitude rule related to the altimeter setting. The difference between the altimeter setting and the actual MSL pressure indicates an altitude discrepancy due to pressure variations.

In this scenario, the altimeter is set to 30.10 in Hg, which is higher than the actual MSL pressure of 29.80 in Hg. The altimeter reads higher than it should because it is compensating for an inflated pressure setting.

The standard atmosphere states that a decrease of 1 inch of mercury corresponds to approximately 1,000 feet in altitude change. The difference in this case is 30.10 - 29.80 = 0.30 in Hg.

Since 0.30 in Hg falls into the category of needing to lower the altitude indication, the calculation shows that if the MSL pressure is lower than what the altimeter indicates, it would mean that the actual altitude is lower. Specifically, 0.30 in Hg translates to approximately 300 feet based on the established rule in aviation meteorology.

Thus, the correct conclusion is that the actual altitude is 300 feet lower than what the