"Say type aircraft and speed"

Steve · #1 09-25-2008, 11:07 AM

After receiving my departure instructions from Salt Lake Clearance Delivery last evening, the controller responded with "Say type aircraft and speed."
The first part is easy but what "speed" is he after? IAS? CAS? Ground speed? Knots or statute? I realize he's plannnig for an orderly departure flow so what data would be best for his purposes?

Steve

Jamie · #2 09-25-2008, 11:16 AM

I'm no expert, but I believe all speeds assigned by and reported to ATC are to be IAS. Every aircraft is required to have an airspeed indicator, but not a CAS/TAS calculator or GPS to calculate ground speed.

Mike S · #3 09-25-2008, 11:21 AM

"Expiremental RV-10, indicating 160kts"

Gives all the info, let him sort it out.

DeltaRomeo · #4 09-25-2008, 11:31 AM

"Experimental. 165 knots (IAS)".

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RVRC · #5 09-25-2008, 11:33 AM

Jamie and Mike are correct. They ALWAYS want IAS in knots!

CONQUEST I Driver

Kahuna · #6 09-25-2008, 11:44 AM

Quote:

Originally Posted by RVRC

Jamie and Mike are correct. They ALWAYS want IAS in knots!

CONQUEST I Driver

Why?
Seems a very lousy number for folks trying to manage positioning

Simon Hitchen · #7 09-25-2008, 11:56 AM

Because its all relative. You can always get two guys or more to fly the same IAS to establish and maintain separation. IFR guys will be flying a filed IAS and asking you your aircraft type and speed allows ATC to slot you into the system. We're always asked for IAS or Mach (same thing just referenced to speed of sound). Works like a charm to provide separation.

turbosaaber · #8 09-25-2008, 12:57 PM

We want ias but our readout on the scope is that of ground speed. BTW...it does not always workout so well...due to altitude changes during sequencing. 1st acft @12000 and 2nd acft descending from fl240 to 12000. I teach our trainees that they can expect 7kts per 1000/ft if both acft are assigned the same ias. That is why we slow you down then speed you back up a bit once we have established spacing. Well that's from a center point of view.

Take care and good topic.....

Kahuna · #9 09-25-2008, 01:28 PM

Between winds, angle intercepts, and altitudes and other complexities, it would seem that someone managing positioning and sequence all the time would always want one number that meant the same to all in all senerios, that being groundspeed. Is there anyone flying in the system today that doesnt have ground speed? I suppose there are, but in very small numbers.
Seems one less task on the controllers to deal with if they all could just use ground speed.

airguy · #10 09-25-2008, 01:37 PM

The problem with that is that then you redesign all the approach and departure paths, and suddenly any change in wind will FUBAR your angles and speeds. The pilot is less aware on a minute-by-minute level of what the winds are than the controller. IAS lets the pilot concentrate on what he (or she) is doing without task saturation in the cockpit trying to maintain a given groundspeed while flying through various wind levels.

If the controller assigns 210 knots to incoming turbines, and consistently sees 235 groundspeeds, it's not gonna take long for him to realize he's +25 with wind at that level and adjust assigned speeds accordingly if needed. If you tried to get EVERY pilot in that string of airplanes to make the adjustment based on a groundspeed that is affected by a continually changing windspeed in climb/descent, you would end up with some sharp guys making the adjustment fast and some dumb ones screwing it up, resulting in an unholy mess very quickly. It's easier for one man (controller) to adjust rather than expecting many (the pilots) to get it right.

I've seen enough stupid human tricks in the air to believe that in many, if not most, cases the controller has a better chance of keeping it straight than the pilots. If we were all professional, nimble-minded, and very current it would work fine - but that's not reality.