Which condition would cause the altimeter to display an erroneous altitude?

The altimeter relies on the standard atmospheric pressure and temperature set by the International Standard Atmosphere (ISA) to provide an accurate reading of altitude. When operating out of ISA conditions, such as in the presence of unusually high or low temperatures or variations in atmospheric pressure, the altimeter may not account for these changes correctly. This could lead to significant discrepancies between the actual altitude and what the altimeter displays due to variations in air density that affect pressure readings.

For instance, if a pilot is flying in a region where the temperature is significantly higher than standard, the air is less dense, and the altimeter will indicate a lower altitude than actual. Conversely, flying in colder conditions where the altitude is higher than ISA pressure will cause the altimeter to display a higher altitude than it truly is. This phenomenon is crucial for flight safety, particularly in areas with rapidly changing weather conditions. Understanding how altitude measurements can be influenced by external atmospheric conditions is essential for accurate navigation and maintaining safe flight.