Final answer:
Pilots must adjust their altimeter to the standard pressure setting of 29.92 inHg or 1013.2 mb immediately upon entering the standard pressure region when climbing, and switch to the local altimeter setting immediately prior to descending into the altimeter setting region.
Step-by-step explanation:
When climbing from the altimeter setting region into the standard pressure region, pilots shall set their altimeters to standard pressure (29.92 inches of mercury or 1013.2 mb) immediately upon entering the standard pressure region. When descending into the altimeter setting region, pilots shall set their altimeters to the appropriate station altimeter setting immediately prior to descending into the altimeter setting region. Understanding this procedure is crucial because atmospheric pressure decreases with altitude, and the altitude reading of an altimeter is based on the atmospheric pressure at the aircraft's current position.
Normal atmospheric pressure at sea level will support a column of mercury about 760 mm high, which is equivalent to 29.92 inches or 1013.2 mb. This is considered standard atmospheric pressure (1 atm) and is the setting used in the standard pressure region. However, as one ascends, the atmospheric pressure decreases, which can lead to inaccurate altitude readings if the altimeter is not properly set to reflect the local air pressure.
For pilots, ensuring the correct altimeter setting by following these procedures is essential for maintaining accurate altitude readings, which are crucial for safe navigation and avoiding terrain and obstacles, especially in areas where the atmospheric pressure is not at the standard setting.