flying on ground speed i.o IAS/Mach # ?

[OscarTango]

Hi, as I do more and more sequencing I often wondered if it would be possible to give an instruction to the aircraft to fly a certain ground speed instead of IAS or a Mach number ?
This would certainly make it easier, but I don't think real traffic is the right environment to try this out... I'm only fully qualified for 4 months now, so forgive me my "unknowingness" ( if that's a word ? )...
BTW, I do area control, not approach... but with sometimes 6 aircraft inbound to EHAM at the same time, we do sequence them :D

[Nightrider]

OT...your training has missed some important steps... groundspeed is the worst to advise. Just think about a nice autumn or spring day with winds of about 50 kn westerly directions above FL 100 and about zero wind at FL 80 with about 30 to 40 knots easterly on the ground...now what do you expect us to do...
What you want is to have all the flying targets on your screen lining up at the same speed. This works only if all use IAS...

I am not aware of any autopilot which can be hooked up to groundspeed...maybe the newest digital gadgets have this feature, I don't know. So with GS instructions you will create some mess because everyone will be more than busy with constantly adjusting power setting and aircraft configuration to match the demands...the only answer you will get is...unable to comply due to safety reasons...

[Genghis the Engineer]

GPS coupled autopilots, which are available mostly for part 23 aircraft, will do this. Autopilots on most part 25 aircraft work on IAS or IMN and won't. Significantly, you can't reasonably fly manually on groundspeed, only a computer could do this. You can't reasonably use procedures which are not available to manual handling.

I suspect that GS coupling may become a good idea when freeflight / open skies starts working properly. But, I only think it'll work in long cruise segments, not terminal work, for reasons as said above.

Also, particularly if large flight level changes are required in cruise, maintaining constant GS is impossible - airliners work on a fairly narrow IAS or Mach No. band, and the relationship between IAS, CAS, and GS will constantly change with altitude.

G

[OscarTango]

Nightrider, we did cover this subject in our training and I did pay attention, but it was all THEORY to me... and theories can often be proven wrong, hence my question.

As I didn't have a background in aviation before I became an ATCO, all my knowledge comes from what they told us, so consider me trained from scratch...

But anyway, now I do know, and thank you for filling in the blanks... and that goes to all you guys who replied. ;)

[Nightrider]

glad to see that you knew this problem already. One simple idea comes to mind, a lot of your colleagues did some so called familarization flights in the past. In BRU it was always very easy to just drop into the R2 office (assuming it does not exist anymore...) but I am sure that you will have luck approaching other airlines there to get some jump seat experience and see the other end of your workplace.
Pilots are more than convinced that an ATCO job is demanding and challenging at times, most ATCOs see our "office" job quiet similar. We need to pull on one string, know each others problems and ideas and it will lead to a much less stressful day for all.
I am completely convinced that any idea which will improve all our situations are most welcomed, so do not stop searching for better ways of what we do now.
The only irritating point in your posting was that the most basic knowledge of our environment appeared not to be as available as it needs to be.

[OscarTango]

Yes, right...I should have thought about the different winds at different levels, I admit. It's just that we check the (ground)speed with this button we have...and speeds might look similar, but when the higher one descends, it suddenly increases speed by a lot of knots... that's what I mean with "theory". In the lectures about sequencing, we were always tought to drop the second one the earliest, 'cause that would slow him down... and it would be easier to lock them on the same IAS.
Well, I have done what I've been told, but found out the complete opposite many times. I could have 12 miles predicted in between, when the AC are at different FL's, but after I descended the first one, I suddenly end up with a predicted 2 miles... so, there goes the "theory"...
I thought about skipping a few steps, by putting them on ground speed, but I didn't think about the impracticality toward pilots.
Oh well, thanks for shining the light ! :D

[ProfessorMCDU]

Two things. First, a ground speed coupled approach is perfectly acceptable and adds a hightened level of safety. In fact, it's the way the Airbus A320 is designed to be flown during an approach. And, there is NO wear and tear on the engines.

Second, during cruise flight - at the same altitudes - ground speed does not become an issue for separation purposes. IAS can be used effectively, and in many cases is used effectively for separation. ie: Trans Ocean, Non-radar environments.

[ProfessorMCDU]

This is absolutely correct. The "FADEC" system takes care of the engines, and on modern airplanes (Airbus) the thrust levers don't move with reactions to auto-thrust inputs.

12000 hours total
2500 Airbus Captain

And, 3 cars! One is 15 years old, with 900,000 KM's and the original engine, trans, etc.


Give my regards to the Engineers....