Under what condition will true altitude be lower than indicated altitude with an altimeter setting of 29.92 inHg?

Under what condition will true altitude be lower than indicated altitude with an altimeter setting of 29.92 inHg?

• A. In colder than standard air temperature.
• B. When density altitude is higher than indicated altitude.
• C. In warmer than standard air temperature.
• D. In standard temperature.

Answer: (A)

With the altimeter set to standard pressure, it translates ambient pressure into altitude using the standard atmosphere. When the air is colder than standard, the actual pressure at a given height is higher than the standard model predicts. The altimeter, interpreting that higher pressure through the 29.92 reference, will indicate a higher altitude than your true height. So your true altitude is lower than what the altimeter shows. In warmer air, the opposite occurs (true altitude would be higher than indicated).

With the altimeter set to standard pressure, it translates ambient pressure into altitude using the standard atmosphere. When the air is colder than standard, the actual pressure at a given height is higher than the standard model predicts. The altimeter, interpreting that higher pressure through the 29.92 reference, will indicate a higher altitude than your true height. So your true altitude is lower than what the altimeter shows. In warmer air, the opposite occurs (true altitude would be higher than indicated).