Definition
An FAA Advisory Circular that provides guidance for using Global Navigation Satellite System (GNSS) equipment for IFR en route, terminal, and non-precision approach operations in the U.S. National Airspace System. It explains how pilots and operators may use GPS-based navigation to meet IFR requirements, including equipment, database, and operational standards. Note: AC 90-94 has been superseded by later ACs (such as AC 90-100A and AC 90-105), but it is referenced in the Instrument Flying Handbook as the historical guidance document for GPS IFR use.
Plain English
An FAA guidance document that tells pilots how to legally and correctly use GPS for instrument flying, including en route navigation and non-precision approaches.
Context Anchor
Seen in instrument procedure planning, especially when the handbook points pilots to FAA guidance on using GPS during the descent and approach phase.
Derivation
Advisory' comes from Latin 'advisare' meaning to consider or counsel — so an Advisory Circular is a circulated document offering FAA guidance. It is not a regulation itself; it explains how to comply with one. The number (90-94) identifies the subject series (90 = Air Traffic and General Operating Rules) and the specific document.
Why Pilots Care
Following its guidance helps ensure the descent and approach are flown safely, legally, and in coordination with ATC.
Intuition Check
Do not read advisory as meaning casual or unimportant. In this FAA context, advisory means official guidance on an acceptable way to do something, even though the circular itself is not usually a regulation.
Example Sentence 1
Before flying a GPS approach in IMC, the pilot reviewed AC 90-94 to confirm the equipment and database requirements were met.
Example Sentence 2
During preflight planning, the crew consulted Advisory Circular (AC) 90-94 for approach considerations in the destination area.