Definition
An Instrument Landing System approach procedure to Runway 28, with the letter Z used to distinguish it from one or more other ILS approaches to the same runway. When two or more straight-in instrument approaches of the same type serve the same runway, each is assigned a different letter from the end of the alphabet (Z, Y, X, W, etc.) so pilots and controllers can refer to a specific procedure without confusion.
Plain English
This is one of several precision approaches to Runway 28 at a particular airport. The 'Z' is just a label that tells you which version of the ILS approach you are flying, because there is more than one ILS to that runway.
Context Anchor
Seen at the top of an instrument approach chart and in an approach clearance or briefing when a pilot is preparing to fly that exact procedure.
Derivation
The lettering convention starts at Z and works backward through the alphabet specifically so the letters are not confused with runway numbers or compass headings. Earlier letters like A, B, C are reserved for circling-only approaches, which is why straight-in versions begin at the far end of the alphabet.
Why Pilots Care
Selecting the correct variant ensures the pilot follows the proper altitudes, routing, decision height, and missed approach instructions for that procedure.
Intuition Check
Do not read Z as part of the runway name or as a quality grade. It is only a procedure identifier that separates this chart from other similar approaches to Runway 28.
Example Sentence 1
Tower cleared us for the ILS Z Runway 28 approach, so I made sure to load the Zulu version and not the Yankee, which had different step-down altitudes.
Example Sentence 2
The ILS Z RWY 28 showed different minimums than the parallel ILS Y approach to the same runway.