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-   -   Standard speed during descent (https://www.pprune.org/atc-issues/489326-standard-speed-during-descent.html)

MD11Man 30th Jun 2012 16:49

Standard speed during descent
 
Hi all,

Just wondering if there is a standard speed during descent, which ATC would expect an aircraft to fly? If yes, what would it be for the B737?

I mainly wonder for the London TMA.

Thanks!

Ninja Controller 30th Jun 2012 22:25

It depends on the level, route and holding situation. If you were heading into a hold for a 10+ minute delay I'd expect you to reduce to minimum clean speed at about 50 miles out from the hold.

Below FL200, a lot of operators seem to fly at about 270Kts if there is little or no delay. Fly whatever speed suits you best, and if you want to change speed significantly don't forget to let us know.

Any particular airfield or route in the London TMA?

MD11Man 1st Jul 2012 04:09

It's for about half the descent into Manchester, before being transferred to Scottish.

One of the reasons I'm asking is that, if I stick to econ descend speeds, the a/c seems to think 250 knots (or a bit lower) seems to be the speed to go for. Just got a feeling last week that controllers didn't really 'like that', so I wonder if there is a speed they'd expect us to fly.

Rossoneri 1st Jul 2012 09:47

From an en-route perspective, 250kts seems slow particularly if there isn't much in the way of delays. I only use 250kts or less if delays are 10mins+. I'd normally expect short haul a/c to be descending anywhere between 270-300kts.

10W 1st Jul 2012 10:04

We have information from several operators that 250Kts is an economical descent speed and that various aircraft types might be flying at it in the descent, something which we might need to take account of in our separation plans. Operators of the same aircraft types might not all do it however.

Fly what you want to, and if ATC need a specific speed, it's up to us to specify it.

250 kts 1st Jul 2012 14:21

We did have a trial into the London TMA about 4 years ago when operators had agreed that 270kts was a reasonable speed for both fuel efficiency and the operation of the network as a whole. Unfortunately the procedure was poorly released to the ATCOs so quickly fell into disrepute despite analysis showing that operators were benefitting in terms of reduced fuel burn.

Some operators (EZY) continue to use 270kts or less as their normal speed so it is always frustrating to hear ATCOs actually speeding them up to stay in front of another company aircraft. In actual fact even some of the more notorious high speed merchants have significantly reduced their descent speeds even though they may have an unrealistic 25 minute turn round to make.

I think it is time that 270kts trial was re-introduced with better communication and training to the ATCOs.

There will always be times when it will be necessary to use high speed but if a speed range 240-270 kts is better for the operators than 270-300kts then why don't we use it and increase awareness of the reasons for it. It does also allow significantly more thinking time on a busy sector.

PointMergeArrival 1st Jul 2012 18:51

In Norway the 2 biggest operators (mostly B73x) have agreed to use 260KIAS during descend. If they for some reason use a different speed they are supposed to advise ATC which they ofcourse seldom do.
A B73x will use about 1kg extra fuel per knot from ToD to FL100(compared to 250KIAS), and unless needed for sequencing or requested by the crew I think ATC should not plan for everyone descending at 270+knots.
Why burn extra fuel going fast nowhere? If you know they'll have to hold why do you expect 270-300 knots?

i_like_tea 2nd Jul 2012 00:47

It all depends on the situation though, doesn't it?

For example, if I am being kept high (happens a lot in busy traffic areas, such as France, Spain, Italy... especially Italy!) then I'm going to be a lot happier if I can maintain a higher speed to descend at a quicker rate. The worst thing is being high, and told to slow down (especially when you've been told to maintain high speed 300kts, and then suddenly you get 220kts and being asked to expedite descent at the same time, DOH!).

Other days, we may have some weather en-route, or may be below profile so perhaps we will want to stick to more specific turb / econ speeds.

I understand the theory behind "one fixed speed", and they have many speed constraints published on the Paris arrivals from a long way out but the realistic terms is they are never stuck to by ATC or by arriving aircraft because every day, environment and situation is different.

Out of interesting, and to clear a rumour up, can you ATC guys see what speed we select? Or just the speed we are maintaining?

Ninja Controller 2nd Jul 2012 06:45


Out of interesting, and to clear a rumour up, can you ATC guys see what speed we select? Or just the speed we are maintaining?
In the London TMA we can see the actual IAS being flown. It's a very useful tool for streaming inbounds and since it's introduction, speed compliance has improved significantly.

Over+Out 2nd Jul 2012 08:11

For the LTMA, if you are given a speed fly that speed.
If you are given standard speeds or nothing is said, fly the airline SOP speed or what you wish and then reduce to 250kts at the SLP.
We can see the IAS you are flying. :ok:

Topjet 2nd Jul 2012 09:08

Mode S
 
We can see the current IAS in the En route (AC) ops room too now so flying slow shouldn't be a problem. The only gripe I have is when operators are filing to fly at 460TAS then are cruising at <M.74 etc without telling us in the en route phase!!!

The Many Tentacles 2nd Jul 2012 09:45

As an en-route UK ATCO I don't care what speed you're flying. If I need you to fly a speed for separation purposes then I'll tell you to fly that speed, if you can't do it then let me know and I'll for Plan B/C/D

Like others have said we can see the IAS being flown and the groundspeed so aircraft flying slowly shouldn't be an issue.

On the beach 3rd Jul 2012 12:26

Initial descent M.80 into 300kts down to about F150 when speed should be reducing towards 250/270kts. Most a/c can live with these speeds and it makes life a bit easier for most air traffic control situations wherever you are in the world.

FlightPathOBN 5th Jul 2012 16:53

What about idle descent...how does that fit in?

What I usually design is a set waypoint at FL10 with a 250kts speed restriction. The ac will calc a TOD, and pull to idle to meet that mark. I know it has issues with non-RNP traffic, but between this, and another waypoint at 5000 with a speed restriction of 180kts seems to balance it out quite a bit.

While this works very well for the location of those designs (which include multiple transitions to a 5nm final,...I am curious on other opinions from ATC on how to work with RNP and non-RNP aircraft...or with CDA, how to work the idle descent from the STAR, and drive it down from 5000...

RVF750 5th Jul 2012 19:55

I'm just a TP jockey, and we got the poster of 270kts into the TMA as well.

We can do that but the fuel burn goes through the roof and our standard descent speed is 230kts now. We're very flexible if it stops problems but personally I don't mind being put to the side if I'm in the way rather than be made to go flat out and be 10-15 minutes early.

Times are tight and I love my job. Saving fuel whenever possible is all I can do to help me keep it in this context.

One question, where does the TMA start on a willo inbound? Is the FL150 considered inside or as far back as DISIT?

I forgot to ask last time I visited Swanwick....

Not Long Now 5th Jul 2012 20:19

TC Midlands, who work the 150L KIDLI inbounds counts as TMA and go up to Birmingham adn across to East Midlands. Ever expanding kingdom....

On the beach 5th Jul 2012 21:21

FlightPathOBN,


"What about idle descent...how does that fit in?"
In a quiet environment or at night, it's generally not a problem, but at airports operating at max capacity it trashes the movement rate and results in those following you having to spend unecessary time in the hold. Or if you are following someone on idle descent, then it's you going around the hold, wondering why.

It's an unfortunate fact these days that operating an aircraft economically is ok for one aircraft but for those following, going into the hold makes the whole idea uneconomical at busy airports. The greatest benefit for all concerned is down to aircraft operating at the mean fastest speed possible. This applies as much on final (160kts to 4nm) as to the en-route phase. One aircraft cruising at M.73 when everyone else wants to cruise at M.80 means that every hour for that particular level, one aircraft has to stay on the ground because that level is not available because of one aircraft flying "economically".

Flying is not a cheap option (despite what LCCs may want you to believe) and so-called "economical" flying is also not necessarily the cheap or best option that airline "bean counters" may want you to believe. One aircraft on idle descent while 6 aircraft from the same company get vectored "x" extra miles or go around the hold once makes a nonsense of the economics of it all.

One radical solution is for Mr. Airbus and Mr. Boeing to make aircraft that don't generate wake turbulence. Mind you getting over the sight of 3 landing aircraft on the runway with you just in the flare might present other perception problems.

Meanwhile, back in the real world, controllers around the world have to cope with the realities of generating increasing amounts of runway and airspace capacity. And I see Mr. Boeing is thinking of adding an extra 1700 aircraft a year for the next 20 years. No doubt Mr. Airbus, not wishing to be outdone, will also do his bit and add an extra 2000 for the next 25 years!

Remember that when you next drive down a motorway and are following someone "cruising economically" at 50mph. Is he doing everyone a favour and saving the planet "x" amounts of CO2 emissions and everyone 3 mpg or is he just making everyone behind 20 minutes late and creating one of those "phantom" queues which result in a 20 mile tailback. Flying is just the same, kind of. :E

On the beach

FlightPathOBN 5th Jul 2012 22:06

On the Beach,

I completely agree with you. While RNP has been sold down the drain with the benefits of fuel savings on idle descent, the reality is that I cannot see how this works, and have been marginally successful in some of the coding tricks mentioned above. Unfortunately, now the funding is all towards a solution that does not work.
When I first got involved with RNP, and the mantra idle descent, (to somehow fund the cost), I struggled with the concept, first off, asking if anyone had talked with ATC about all of this.(which of course I found out NOT)
So in trying to balance this, there are still certain variables to work with...

For me, Econ cruise means the ability to meet the timing, without demurring or a go around...if you have to knock off 5 kts enroute, to drive in, then that is econ cruise...

What is econ for one ac is not for another....

You have a slot, you make that slot, TOD off the enroute can still be idle descent to the hard point at the outer marker. The computer can calc this out, just back out the time needed to be at that waypoint.
We can work this automatically through the intent bus, and ADSB already.

I hate when I get feedback like you are saying, and it is really difficult, on CDA, with idles descent, when you have a 747 F, and an A320 following..

As far as turbulence, if you have coded routes, that can easily solve that issue. Whn you get in close, have the heavies on a 2.8GPA and the mediums on a 3.1GPA...everyone will be fat and happy. That all fits within existing ILS GPA and the lighting...

As you guys are aware, wake turbulence is being looked at with real time systems. When that all gets sorted out, the first thing you will see is a change in SOP for approach. Then you will see Boeing and Airbus getting serious about their wing designs, which currently, date from when?
The flex wings on A350 and 787 may have some potential, but if the current computational fluid dynamic models are still in use, don't expect too much from that. Just look at all of the recent 'new' winglet configurations that all are 5-7 percent more efficient than the last or the 'other' manufacturer...

Stepping back, the wake sep is one of the biggest constraints in the mix for ATC...look for a radical change in the next few years...

250 kts 15th Jul 2012 16:26


We can do that but the fuel burn goes through the roof and our standard descent speed is 230kts now. We're very flexible if it stops problems but personally I don't mind being put to the side if I'm in the way rather than be made to go flat out and be 10-15 minutes early.
What company is that using 230kts?

The Fat Controller 15th Jul 2012 18:19


We can do that but the fuel burn goes through the roof and our standard descent speed is 230kts now. We're very flexible if it stops problems but personally I don't mind being put to the side if I'm in the way rather than be made to go flat out and be 10-15 minutes early.

What company is that using 230kts?
As the pilot says he is a turboprop driver, I would guess it is FlyBe.


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