In what conditions is a pilot responsible for providing margin for altimeter error?

The responsibility for providing a margin for altimeter error is particularly relevant when flying at or below the Maximum Elevation Figure (MEF). The MEF signifies the highest elevation that should be safely navigable in a given area while allowing for any possible errors in altimeter settings. This figure includes a safety margin for obstacles, ensuring pilots maintain a safe altitude above terrain.

Maintaining altitude above the MEF helps in preventing controlled flight into terrain, particularly in varying atmospheric conditions that might affect altimeter readings. By adhering to this guideline, pilots can ensure they are flying with a substantial buffer against potential discrepancies in altitude indications due to altimeter malfunction or environmental influences, such as pressure changes.

In contrast, situations like flying in mountainous terrain or navigating urban environments do have their challenges but may not impose the same specific requirement for alphanumeric margins as dictated by the MEF. Similarly, while IFR regulations require strict altimeter settings and adherence, they do not inherently stipulate a direct responsibility for providing a margin against altimeter error.