Why is the altimeter setting important before an IFR flight?

The importance of the altimeter setting before an IFR flight primarily revolves around maintaining the correct altitude above sea level. The altimeter is a device that measures atmospheric pressure to determine the altitude of the aircraft. When the altimeter is set correctly to the current altimeter setting, it enables pilots to ensure that they are flying at the intended altitude above sea level, which is critical for safe navigation and avoiding terrain.

Flying at incorrect altitudes can lead to potentially dangerous situations, such as terrain or obstacle collisions, especially in conditions of low visibility where the pilot may be relying solely on instruments. Therefore, ensuring that the altimeter is accurately set to the current pressure helps maintain situational awareness and safety during the flight, making it a fundamental aspect of pre-flight preparation for IFR operations.