When transitioning between the standard pressure region and altimeter setting region, when should the altimeter setting be changed?

The correct choice emphasizes the importance of changing the altimeter setting while still within the standard pressure region. This is crucial in aviation because altimeters rely on current atmospheric pressure to indicate accurate altitude above sea level.

When operating in the standard pressure region, pilots use a standard setting of 29.92 inches of mercury (Hg) to maintain a consistent reference for altitude. As aircraft approach the transition to an area with local altimeter settings, it is necessary to switch the altimeter setting before entering this region to ensure that altitudes are accurately reported relative to the local air pressure conditions. This proactive approach helps to avoid altitude discrepancies that can lead to potential safety issues, especially during landing and takeoff phases where precise altitude awareness is critical.

Changing the setting in the standard pressure region ensures pilots have the appropriate information for altitude awareness as they transition into the altimeter setting region where local conditions might be significantly different. This operational practice helps in maintaining situational awareness and enhances safety during flight operations.