Why is it necessary to match the altimeter setting to local pressure?

It is necessary to match the altimeter setting to local pressure to ensure accurate altitude readings. The altimeter in an aircraft functions by measuring changes in atmospheric pressure; it translates these pressure changes into altitude. When flying, if the altimeter is set incorrectly—such as using a standard pressure setting rather than the local setting—it can lead to misleading altitude information. This could potentially result in flying at dangerously incorrect altitudes, particularly when approaching airports, where precise altitude awareness is crucial for safe operations.

Matching the altimeter setting to the local pressure gives pilots a reliable reference for altitude above sea level and enhances situational awareness, especially in proximity to terrain or other aircraft. Hence, accuracy in altitude readings is fundamental for safe navigation and operational safety.