In aviation, a time such as "1753Z" uses which time reference?

Why: The FAA study guide states: "the time... is always given in coordinated universal time (UTC). A 'Z' is appended to the end of the time to denote the time is given in Zulu time (UTC) as opposed to local time," and separately defines "Zulu time—a term used in aviation for UTC, which places the entire world on one time standard."

• Contradicts the source directly: the "Z" suffix specifically denotes UTC instead of local time, not local time itself.
• Invents a fixed offset between "Greenwich civil time" and UTC; the source treats Zulu time and UTC as the same single worldwide standard, not two separate offset systems.