Decision Height

Decision Height (DH) — or Decision Altitude (DA) when referenced to mean sea level — is the specified altitude or height during a precision approach at which the pilot must decide whether to continue to landing or execute a missed approach. If the required visual references (runway lights, approach lights, or the runway itself) are not clearly visible at DH/DA, the pilot is required to go around.

The distinction between DH and DA is technical: DH is referenced to the threshold elevation (height above the runway), while DA is referenced to mean sea level (altitude on the altimeter). In practice, both represent the same point in the approach.

Typical DH/DA values:

• CAT I ILS: 200 feet (most common)
• CAT II ILS: 100 feet
• CAT III ILS: 50 feet or less (some with no DH at all)

For non-precision approaches, the equivalent concept is MDA (Minimum Descent Altitude), which the pilot must not descend below unless the runway is in sight.