Definition
A specific fix on an instrument approach procedure defined as the point located 1 nautical mile, measured by Distance Measuring Equipment (DME), from the I-SNA localizer antenna. The 'I-SNA' identifier refers to the localizer ground station serving the runway (in this case, the ILS at Santa Ana / John Wayne Airport), and the '1 DME' portion specifies the slant-range distance from that station at which the fix is established.
Plain English
A named point on an approach chart that sits exactly 1 mile from the runway's localizer antenna, as measured by the airplane's distance-measuring equipment. When the cockpit display reads 1.0 from the I-SNA station, you are at this fix.
Context Anchor
Seen on instrument procedure diagrams and in path-and-terminator leg examples, where a leg may begin, end, or be defined by reaching a specific DME distance from a facility.
Derivation
The 'I-' prefix is the standard ICAO convention for localizer identifiers, distinguishing them from VOR or NDB stations. 'SNA' is the airport identifier for John Wayne Airport (Santa Ana). '1 DME' simply states the distance in nautical miles from that ground station. Knowing the prefix convention helps decode any localizer-based fix you see on a chart.
Why Pilots Care
Provides a precise, repeatable point for altitude and course changes when flying in clouds or at night.
Grounding Statement
Picture flying the published path and watching the DME count down until it reaches 1.0; that published position is the I-SNA 1 DME fix.
Intuition Check
Do not read “1 DME fix” as any point one mile away in any direction. In this procedure context, it means the published point reached at 1.0 DME while flying the specified path.
Example Sentence 1
The procedure requires the aircraft to cross the I-SNA 1 DME fix at or above 560 feet before continuing the descent.
Example Sentence 2
Procedure instructions required crossing the I-SNA 1 DME fix at or above 2,000 feet.