For example, instructing an aircraft to maintain a speed of 200 knots until it is 10 nautical miles from the destination / runway threshold?
What would an ATC command telling a pilot to maintain a certain speed until a certain distance from the destination sound like?
Typically, the speed assignment would be to maintain a specific speed until reaching a definable point (dme fix, navaid, RNAV/GPS fix/waypoint, visual reference point, etc.) as opposed to (a pilot estimated) 10 nautical miles (NM) from a destination or runway threshold. Although, if the aircraft is equipped with RNAV/GPS equipment the crew could create a waypoint/fix 10 NM from the airport/runway threshold.
The Phraseology would be something like: (could be some variation depending on the type of fix/point involved)
"N12345, maintain two zero zero knots until one zero miles from XYZ (fix/navaid/waypoint, etc.)"
1$\begingroup$ An addition to this answer: sometimes known visual points can also be mentioned, for example: at my base (CYXX), they mention "the highway" and "the power lines". A typical instruction would be "WJP expedite cruise until you're over the power lines". $\endgroup$ Aug 27, 2022 at 4:14
In the united-states it would sound something like this, in the absence of an otherwise-useful named fix/waypoint/NAVAID:
Citation 3AB maintain two zero zero knots until ten-mile final.
You are more likely to hear "five-mile final" as that is the latest point ATC is allowed to require the pilot to fly a specific speed, as spelled out in FAA JO 7110.65 5–7–1:
b. Do not assign speed adjustment to aircraft: 4. Inside the final approach fix on final or a point 5 miles from the runway, whichever is closer to the runway.
$\begingroup$ Shrug. We say that kind of thing with some regularity—not speed control necessarily (although sometimes) but more often for sequencing arrivals: "Enter right base for a three-mile final." "Cleared visual approach, join no closer than a five-mile final." I think it's perfectly acceptable to let pilots do pilot things to estimate their position with respect to a runway, if we're using single-digit numbers of miles (and I don't expect to-the-foot accuracy either). $\endgroup$ Aug 28, 2022 at 11:34