At 11,000 feet with an ambient temperature of -7°C, how does the true altitude compare to the indicated altitude?

• A. Lower
• B. Higher
• C. The same
• D. Cannot be determined

Answer: (C)

Temperature deviations from ISA affect how the altimeter’s reading translates to actual height. The altimeter assumes a standard atmosphere, so the height of a given pressure surface changes with temperature. In colder-than-ISA air, true altitude is lower than indicated; in warmer-than-ISA air, true altitude is higher.

At 11,000 feet, the ISA temperature is about -7°C. Since the ambient temperature is -7°C, conditions match ISA, so there’s no temperature-induced error. The pressure surface at that altitude corresponds to the same height, meaning true altitude equals indicated altitude.