Definition
An instrument approach procedure that contains one or more design elements outside the criteria of standard TERPS (Terminal Instrument Procedures) -- such as steeper-than-normal descent angles, higher-than-standard minimums, unusual missed approach paths, or course alignments that exceed normal tolerances -- typically because surrounding terrain, obstacles, or airspace prevent a conventional procedure from being built.
Plain English
An instrument approach into an airport that doesn't follow the usual design rules. Something about the airport -- mountains, obstacles, or limited airspace -- forced the procedure designers to build it differently than normal, and pilots need to know that before flying it.
Context Anchor
Seen in special airport qualification material, approach briefings, and airport comments where an airport has procedures that require extra attention or specific authorization.
Derivation
Nonstandard' simply means 'not following the standard.' The standard here is TERPS -- the FAA's published criteria for how instrument approaches are normally designed. When a procedure has to break one of those rules to be flyable at all, it's labeled nonstandard so pilots are alerted.
Why Pilots Care
A pilot must hold special airport qualification before flying one of these approaches; attempting it without the required training can lead to unsafe operations or regulatory violations.
Intuition Check
Nonstandard does not mean “made up” or “optional.” It means the approach is published or authorized, but it has unusual requirements that must be followed exactly.
Example Sentence 1
Aspen's approach was flagged as a nonstandard instrument approach, so the captain reviewed the steeper descent angle and higher minimums during the briefing.
Example Sentence 2
After completing special qualification training, the pilot was authorized to fly the nonstandard instrument approach into the mountain airport.