How do warm temperatures affect the altimeter readings?

Warm temperatures have a significant effect on the altimeter readings due to the principles of atmospheric pressure. An altimeter measures the height of an aircraft above sea level by detecting changes in air pressure. Under standard atmospheric conditions (ISA), the air is cooler, and the altimeter is calibrated accordingly.

When the air is warmer than standard, it expands. This leads to a decrease in air density at a given altitude compared to the standard atmosphere. Consequently, the altimeter, which relies on the measurement of air pressure to determine altitude, will register a lower pressure than that which corresponds to the actual altitude. As a result, the aircraft will be at a higher true altitude than what the altimeter indicates. Thus, in warm temperatures, the indicated altitude is lower than the true altitude, which can be critical for pilots to understand for safe altitude management.

Understanding this phenomenon is essential for pilots, as failing to account for warm temperatures can lead to flying at an altitude that is lower than intended, potentially causing unsafe flight situations, especially during takeoff and landing phases.