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While dealing with Takeoffs and Landings controllers provide speeds to pilots for different phases of the flight, specially during a landing approach.

How do they know which speeds are safe for all the different models operating to and from their airport? Are they provided with that data daily or they have to remember those speeds?

If a general answer is not possible I would be more interested in knowing about stall speeds during a landing approach. Obviously they will be different for different aircraft in different conditions.

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    $\begingroup$ ATC doesn't actually assign landing airspeeds. They simply clear them for the approach and from then it's up to the pilots to establish the appropriate landing speed for their aircraft. Further back in the descent or cruise, ATC may issue a speed restriction, but that is never low enough to come close to a stall. $\endgroup$
    – Ben
    Dec 27, 2016 at 22:31
  • $\begingroup$ Don't they say Reduce speed to X Knots? $\endgroup$
    – Hanky Panky
    Dec 28, 2016 at 1:19
  • $\begingroup$ If they need to slow them down (or sometimes speed them up) for traffic purposes, yes, but that falls under the last sentence in my comment. But if there is no traffic, usually they just let the pilots manage their speed themselves. Pilots do not need a clearance to change speed, unless ATC has asked them to maintain a specific speed. $\endgroup$
    – Ben
    Dec 28, 2016 at 2:08
  • $\begingroup$ I see. Thanks for that! $\endgroup$
    – Hanky Panky
    Dec 28, 2016 at 2:30

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No because aircraft are categorized by their speed at the runway threshold (1.3 times stall speed).

enter image description here
VAT —Speed at threshold used by ICAO (1.3 times stall speed in the landing configuration at maximum certificated landing mass)

By knowing the category, ATC is able to use appropriate speeds. The category is not actually listed anywhere, so the controller will have to know the approach category by heart for each aircraft type. E.g. if the controller sees "B738" as the aircraft type in the flightplan, they have to know that the corresponding approach category is C.

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    $\begingroup$ @HankyPanky The pilot might also refuse a speed command by saying "unable". ATC would then need to adjust their plan to accommodate. $\endgroup$
    – Simon
    Dec 27, 2016 at 11:37
  • $\begingroup$ I see, thanks Simon! $\endgroup$
    – Hanky Panky
    Dec 27, 2016 at 13:14
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    $\begingroup$ I think the point was that the pilot in command is responsible. If the concern is that ATC would inadvertently cause an aircraft to stall the PIC would still be held responsible. $\endgroup$
    – user6035379
    Dec 27, 2016 at 16:38
  • $\begingroup$ What to do if an aircraft has a V-AT above 210 knots? $\endgroup$
    – Vikki
    Feb 3, 2019 at 5:05
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    $\begingroup$ @Sean: "What to do if an aircraft has a V-AT above 210 knots?" When a new problem arises, we adapt our practices. Not a big challenge here, we could create a "F" category. In the meantime, or if for some reason a pilot needs to approach or land at an abnormal speed, the crew and ATCO can still agree on this speed. Categories are only a mean to speed up this discussion. $\endgroup$
    – mins
    Feb 3, 2019 at 7:25

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