ATC assigning "Ground Speed" for sequencing.

[Jerricho]

Question for you pilot types (especially Turboprop drivers)

Let's say you're flying into Terminal airspace and you're assigned a ground speed rather than IAS for sequencing. My brain only works in IAS, but I supposed with GPS and all that good gear it's possible.

Good thing or bad thing or couldn't care thing? Discuss........

[AuxBatOn]

Question for you pilot types (especially Turboprop drivers)

Let's say you're flying into Terminal airspace and you're assigned a ground speed rather than IAS for sequencing. My brain only works in IAS, but I supposed with GPS and all that good gear it's possible.

Good thing or bad thing or couldn't care thing? Discuss........

THe only thing I could see is that a groundspeed is going to require more power changes to accommodate for wind. Personally, I'd rather have an indicated air speed on vectors.

[ywg-atc]

Jerricho: I thought manops only lets us assign speed in terms of indicated or mach number? Is assigning ground speed allowed? I haven't looked at manops in a while.

[Jerricho]

You are correct reference MANOPS ywg-atc. IAS or MACH are the only things referenced in MANOPS regarding speed.

Having heard it used more than a few times recently, I thought I would get a pilot point of view. Personally, it's making me cringe (MANOPS aside) as it has caused some confusion. But, some drivers must be accepting it......is it begrudgingly or best attempt at attaining the specified ground speed?

[TG]

Same question could be asked regarding radar vectors. We could work out wind corrections and give you a constant 'ground' heading.
But, as AuxBatOn said, it would require more work on our side and I guess this would give you something more constant on your radar screen (if you can trust pilots)

Jerricho, unless I'm missing something, if a couple of aircraft are given specific IAS for sequencing they will all encounter the same upper winds at some point or another.
They might play accordion during descent/ascent but it will be at the same places and this should not affect their time between each other no !? (distance yes but timing no)

Regardless, flying a ground speed instead of an IAS one is not something I will want to do during an approach (especially in windy conditions)

[Check Pilot]

Asking for a particular groundspeed would place an undue workload on a pilot. The winds change with altitude, sometimes very quickly, particularly in the terminal phase on either departures or arrivals. It's busy enough getting the aircraft configured for the appropriate phase of flight but to also now need to be concerned about power settings or climb or descent rate to also be having to look at a GPS groundspeed and adapting to the changing winds in climb of descent is just adding an additional workload all the while respecting navigation issues on either departure or arrival.

It's busy enough just getting the lateral navigation stuff done correctly, much less what now becomes a vertical requirement as well.

Pilots are adept at holding IAS at a particular value but to have to look at 2 different speeds - IAS and GS - puts an extra unwanted and unneeded workload on the pilot just when it is least desirable. Some autopilots are very capable of holding a very accurate IAS, but I know of none that can couple up to groundspeed. It would likely result in a few wild vertical speed and IAS rides that would not only get the pilots PO'd but also the controllers who might be looking for a smooth altitude transition to maintain separation.

6 of one or half a dozen of the other, take your pick.

A bad idea. Stick with IAS restrictions. I think any proposed change to MANOPS that mandated GS restrictions would likely result in a giant pile of complaints. I would refuse any such instruction if it was given to me. I'm very amenable to IAS requests and comply with them, but a particular groundspeed? Forget it.

[Willis Nigh]

I often wondered while being vectored way out on a 15-20 mile final why the controller didn't just ask us to reduce groundspeed ahead of time. I'd imagine it's just a workload thing. I will request a reduction in speed if I'm not number one for the approach and I'm being vectored away from the airfield. It seems to work well. As fuel conservation becomes a bigger issue the system will have to be changed towards what you're suggesting. You're ahead of your time Jerricho.


For small-medium category aircraft I don't think it would be too difficult if you asked the pilot to reduce average groundspeed to a certain range (+/- 10 kts). Even in changing winds aloft.

[Jerricho]

You're ahead of your time Jerricho

I wish.

As I said, I (an others) have been on the receiving end of this one (queue disparaging lewd comment). First aircraft comes over no speed assigned, second aircraft has been "assigned the ground speed" of the one their following. Maybe it is the way of the future?

[ywgflyboy]

Personally I feel (taking into account the poor math skills of some people I have flown with) that "G-ABCD reduce/increase speed ## knots" is fairly direct and eliminates room for mathematical error for those flying without GPS, LORAN ground speed readouts.

[parrot_head]

I'll sometimes use groundspeed when I have an aircraft on a visual approach behind another aircraft. ie" 'ABC your 4 miles behind your traffic he's ground speed is 60 kts slower ( or he's grounding 160), contact tower....." Sometimes I get a "thanks for the heads up" and sometimes I get a "yeah we know... we see him remember?".

[ahramin]

While there might be circumstances where I could see this being useful, it does open a huge can of worms. As others have said it can take far more effort to maintain a groundspeed than an airspeed, and no autopilot will follow a groundspeed (except that some will adjust groundspeed to arrive at a fix at a certain time).

But I suppose if a groundspeed was requested I wouldn't find it a problem. Winds don't typically change that fast.

[Jerricho]

Winds don't typically change that fast.

Ah, but what happens if you were given a 30 degree turn?

[the_professor]

If you are asked to maintain a ground speed, call the ACC shift manager after you land (phone numbers are in the CFS, collect calls are accepted), and demand an explanation. This is a nightmare scenario for pilots, and contrary to ATC regs, as previously pointed out. Only a lazy or ignorant controller would attempt this, and they should be shut down immediately. They're not paid $130k+ so that they can transfer workload to pilots, especially without having any clue as to the implications of this illegal instruction when it comes to the cockpit.

(the above is not directed at Jerricho in any way)

[ahramin]

Winds don't typically change that fast.

Ah, but what happens if you were given a 30 degree turn?

Then you make 1 small adjustment to your power setting and continue.

[AuxBatOn]

ahramin,

Winds and TAS change dramatically with altitude normally. Why add workload in an already busy phase of the flight, when the current method works? If it ain't broken, don't fix it.

If all the aircraft fly the same IAS on a similar profile, then their ground speed should be pretty close.

[ahramin]

AuxBatOn, we must be flying in very different parts of the world. I rarely see anything close to a "dramatic" change in winds while climbing or descending, the little wind arrow on the EFIS just increases fairly steadily and might change direction a bit. For example, here are the current FDs overhead:

YVR 3000 6000 9000 12000 18000 24000 30000 34000 39000
17-21 1305 9900+01 2810-03 2917-08 3032-14 283259 295042 295152 295463
21-06 1307 1809+02 2114-02 2318-07 2739-13 284942 284853 296964 284360
06-17 1623 1721+00 2329-02 2430-06 2242-18 224743 224552 234159 254361

Only 1 random sample but it confirms what I usually see. A look at the bottom 12 000 feet shows a worse case gs change of 15 knots on the way down due to winds, and the TAS change in this altitude range is minimal.

I don't know if there is any merit to this idea myself, especially in Terminal Airspace, but if someone at ATC decides that it can help, my workload can handle it. I'm not suggesting that you should be able to handle it, I once flew an airplane that the only way to see the groundspeed was to look down at the GPS implanted into the floor boards. I would not have accepted a required groundspeed in that plane. But in my case, groundspeed is one of those parameters that I am aware of normally anyway.

What I would find annoying is it's just not something any FMS I am aware of will handle. Time over a fix, sure. Mach #, airspeed, sure.

I would certainly find flying a given groundspeed easier to deal with than runway changes all the way in!

[AuxBatOn]

Lets say you are assigned to maintain 300 kts G/S on decent from FL390 to 12000', on a heading of 290T

At FL390, you'll need to maintain 194 KIAS
At FL300, you'll need to maintain 220 KIAS
At FL180, you'll need to maintain 245 KIAS
At 12000, you'll need to maintain 250 KIAS

This is quite the changes (that have to be made continually) to maintain a constant Groundspeed, vice keeping a constant Mach Number until transition, then maintain a constant IAS.

[ahramin]

Like I said, I think it would be a lot less work to change your IAS 2 knots per thousand feet than to reprogram and rebrief an approach.

Tell you what though, I'll give it a try next time I have the chance and report back with actual results. Anyone else want to give this a go?

[Jerricho]

Please not into YWG, coz I'll start cringing again......

[ywgflyboy]

Please not into YWG, coz I'll start cringing again......

When you working next?