What must be used for all CAT I approaches regarding altimeter setting?

For CAT I approaches, using barometric altimeter minimums is essential because they are the standard measurement for determining altitude and ensuring safe minimums during the approach phase of flight. Barometric altimeter settings provide accurate altitude readings that are crucial for maintaining the correct vertical profile relative to the runway and the decision height. This reliance on the barometric altimeter aligns with FAA requirements and ensures pilots are adhering to the established safety protocols.

Utilizing barometric measurements helps pilots to gauge their altitude accurately above ground level and make informed decisions regarding approach and landing. Consistency with barometric altimeter settings is critical during diminished visibility conditions that often accompany CAT I approaches.