What is a key feature of the MDH in instrument flying?

The key feature of the Minimum Descent Height (MDH) in instrument flying is that it is expressed in Mean Sea Level (MSL). This is crucial as the MDH provides pilots with an altitude reference that is standardized across different environments and conditions, ensuring that they maintain a safe altitude above the terrain or obstacles in the area during an approach.

When flying under instrument flight rules (IFR), pilots utilize MSL measurements to make accurate altitude decisions, ensuring safety in both approach and landing phases. The MDH serves as a critical point at which a pilot must either continue the descent to the runway or execute a missed approach if visual references are not achieved.

In this context, while other aspects of instrument approaches, such as decision points and fixed points on the Instrument Approach Procedure (IAP), are essential, the expression of MDH in MSL is what distinctly identifies it as a standard reference point for altitude in the approach phase.