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

• A. Lower than the actual altitude above sea level.
• B. Higher than the actual altitude above sea level.
• C. The same as the actual altitude above sea level.
• D. The altitude above sea level would be undefined.

Answer: (A)

The key idea is that the altimeter shows your height relative to the pressure setting you dial in. If you move from an area of low pressure into an area of higher pressure but don’t reset the altimeter, the ambient pressure at your true altitude is higher than the setting implies. The instrument interprets that higher pressure as being at a lower altitude, so it underreads. In other words, it will indicate a lower altitude than you actually have. If you had reset to the higher local pressure, the reading would then match your true height. The other options don’t fit because they would require the instrument to read higher than you are, or to be undefined.