HBadger wrote:
“what’s your speed”
All regular traffic transmits their IAS through ADSB, so there’s no need to ask. The controller can add or substract 10 knots to the readout and ask for it if needed for sequencing. If you don’t radiate your speed, they have to ask.
Yeager wrote:
Further to that – where are you going to read the TAS from in an analog aircraft? Which instrumentation indicates TAS?
Every basic and/or old steam gauges plane I have flown in has on the airspeed indicator a rotating bezel where one sets pressure altitude against outside temperature, and this sets a second scale from which TAS can be read. I didn’t expect “a large fleet of turbo props out there” that doesn’t have that.
lionel wrote:
Every basic and/or old steam gauges plane I have flown in has on the airspeed indicator a rotating bezel where one sets pressure altitude against outside temperature, and this sets a second scale from which TAS can be read. I didn’t expect “a large fleet of turbo props out there” that doesn’t have that.
Ok, cool, which basic old steam airplanes would that be, out of curiosity? Maybe it´s not so unusual in the smaller GA fleet to have such an airspeed indicator (having a “rotating bezel” and TAS)? I have never seen such an instrument in any “basic” aircrafts that I´ve flown including the Bonanzas.
I´m familiar with the type of indicator, I didn´t realize these were common at all.
I was referring to turbo props airplanes in their classic cockpit layout such as Beechcraft family 200/1900, Fokker 50s, ATRs etc. all of which do not have airspeed indicators with TAS (display option) – the type of turbo prop airliners that traditionally occupy the airspace at airports where ATC often utilize speed control. I don´t even think, but don´t remember, that the upgraded EFIS cockpits (turbo props) have TAS displayed as standard. I´m trying to recall it, but I don´t think the Crash8-Q400 EFIS cockpit had TAS displayed either – but memory may fail me.
The ATR cockpit (youtube video) has it display on a separate digital instrument (I´ve never flown this family).
https://www.airteamimages.com/beechcraft-1900_D-CBCC_raytheon_46520_large.html
https://www.flightvectors.com/Aircraft-Cockpit-Posters-Procedure-Trainers/Regional-Jet-Cockpit-Posters-Procedure-Trainers/ATR/
https://www.airplane-pictures.net/image166228.html
lionel wrote:
thought they want TAS. Like in cruise when they don’t have radar (we are not used to that in Europe) and they are doing time-based separation based on self-reported positions. Like the speed that is in your flightplan (and that theoretically you are not allowed to deviate by more than X% without ATC clearance, I think X is 5?) is TAS."
Enroute separation without radar uses ETA over waypoints. No need to mention speed.
Yeager wrote:
Ok, cool, which basic old steam airplanes would that be, out of curiosity?
C172, C182, C82T and PA28. You explain that there is a “middle ground” of glass cockpits that don’t show TAS. Thanks, interesting.
172driver wrote:
@lionel so you’re gonna fiddle with this dial during an approach? Hope not. In any case, unless you’re flying to some high altitude airport, IAS and TAS are going to be virtually the same during an approach.
Well, in the example I gave the airport is about 500ft elevation, but the question came well before approach, during arrival, or even “pre-arrival cruise descent”. I don’t remember my particular IAS nor altitude at the time, but it must have been at most 160kts and at least FL080, respectively.
HBadger wrote:
“what’s your speed”
One thing nobody mentioned is that the question is triggered by the target aircraft flying a speed outside either published approach (or departure) speeds, or expected speed, and can be for a low as well for a high speed.
Flying a jet and coming high speed on an intercept might have ATC ask the same question as a SEP loitering along the glide 
Dan, interesting comment. It actually was not the case on paper – I was flying pretty much as in the FPL and also according to my plane’s performance. But they are more used to jets and if you show up in a SEP, they start trying to form a mental picture of what you can and cannot do. Even if they might know the plane’s performance envelope, the inquiry is still very valid, because as alluded to by someone above, possible performance highly depends on factors such as IMC vs VMC, Turbulence, Pilot’s wellbeing etc.
For example turbulence penetration speed is 133kts in a SR22, much slower than a jet I guess, and ATC doesn’t know your situation.
HBadger wrote:
For example turbulence penetration speed is 133kts in a SR22, much slower than a jet I guess, and ATC doesn’t know your situation.
For approach speed categorization look for ICAO DOC 8168, or if no official referencing required Skybrary is useful:
https://skybrary.aero/articles/approach-speed-categorisation
FYI info and as practical example. On our Gulfstream G650ER (ICAO Category C and Wake Turbulence Category Medium (136T<MTOW>7000KGS), our Vref (Vat/Threshold) speed is normally in the range of 115-125KIAS (depending on landing weight (usually fuel remaining!)). On a “normal” day (light winds, no icing etc.) I´d add +5KIAS, so from 1000ft AGL (stabilized approach concept) to Threshold we´re looking at 120-130KIAS, so this would be somewhat less than most medium airliners (A320/B737/XXXX)). Normal ATC approach request would be something like “maintain speed 160 (KIAS) until 4 miles (NM)”.
