Point taken on the date of the Notam, yes it’s AM on 1st April, so it can qualify as an April Fool’s joke.
Notwithstanding that, there are many of the cosseted inept drawing significant government salaries who are quite capable of generating such a Notam.
Research the “Below 10,000 ft in controlled airspace” rules in Australia and many other countries.
In all cases the 250 kts is 250 KIAS, i.e. indicated airspeed.
The intent of the 250 KIAS is similar to the use of QNH below 10,000 ft, it establishes a common point of reference or datum to all aircraft below 10,000 ft.
250 kts IAS at sea level is near enough to 250 kts True Air Speed (and 250 kts Ground Speed with Nil wind).
Now look at 250 KIAS at 10,000 ft with, for our Northern region, a typical temperature of +10 degrees C.
A quick play with the whiz wheel will convert this to 287 kts TAS. Busted ?
Now add a 30 kt tailwind, and now would paint as 317 Kts Ground Speed !
Busted again ?
Radar, ADS B and other surveillance methods see ground speed, or rate of closure, not indicated or true air speed.
If this was an April Fool’s joke, lets laugh about it.
If not, what can be done about steering some common sense toward the authors?
Its their trainset.