Definition
An altitude depicted on an instrument approach chart requiring the aircraft to maintain that exact altitude at the applicable fix, segment, or fix-to-fix portion of the procedure. Shown on the chart with lines above and below the altitude figure (e.g., underlined and overlined).
Plain English
An altitude you must fly at exactly when you reach a specific point on an instrument approach — not above it, not below it.
Context Anchor
Seen on instrument approach charts and some arrival or departure procedures, often at a named point or along a specific part of the route.
Derivation
"Mandatory" comes from the Latin mandatum, meaning a command or order. In aviation charting it signals that the altitude is required, not advisory — flying higher or lower is not an option.
Why Pilots Care
Maintaining the exact altitude protects terrain clearance, ensures proper traffic separation, and prevents regulatory violations during instrument operations.
Intuition Check
Do not read “mandatory” as “important but flexible.” In this FAA use, it means the published altitude must be complied with exactly unless a controller assigns something different.
Example Sentence 1
The chart showed a mandatory altitude of 3,000 feet at the final approach fix, so we leveled off precisely at 3,000 before continuing inbound.
Example Sentence 2
The approach plate showed a mandatory altitude of two thousand eight hundred feet over the step-down fix.