When are you required to use a barometric altimeter during an approach?

Using a barometric altimeter is crucial for ensuring safe altitude references during approaches, particularly when determining Minimum Descent Altitude (MDA). The MDA is the lowest altitude to which a pilot can descend in visual flight rules before visual reference to the runway is required. Accurate altitude information is necessary to maintain safety and to avoid terrain or obstacles.

The barometric altimeter provides the altitude in relation to the standard atmospheric pressure. In conditions where precision is required — such as when reaching MDA during an approach — the correct atmospheric information from the barometer is vital to ensure that pilots descend only to the appropriate altitude without risking safety. By utilizing a barometric altimeter at this stage, pilots can confirm they are at the correct altitude, contributing to a safe approach and landing process.

In contrast, other scenarios, while they may involve altitude measurements, do not necessitate the same level of reliance on a barometric altimeter. Visual approaches and initial climb-out may not always pose the same risks for altitude errors that would lead to dangerous situations, hence do not have mandatory requirements tied to the barometric altimeter for those specific phases.