"On transition"
Thread Starter
Join Date: Oct 1999
Posts: 222
Likes: 0
Received 0 Likes
on
0 Posts
"On transition"
Just a question as to what ATC ( UK south ) expect?
We were descending at M0.84 with a planned 270 KT transition and were told 250 or below on transition, FMC reprogrammed and allowed the A/C to slow on the transition.
A rather curt transmission to the effect of I told you 250 or less followed after a couple of minutes.
So if you ask us for a speed on transition when do you expect it- my assumption was at the Mach/Airspeed transition, which for us is driven fron the FMC , but clearly in this case I was wrong?
Thanks.
We were descending at M0.84 with a planned 270 KT transition and were told 250 or below on transition, FMC reprogrammed and allowed the A/C to slow on the transition.
A rather curt transmission to the effect of I told you 250 or less followed after a couple of minutes.
So if you ask us for a speed on transition when do you expect it- my assumption was at the Mach/Airspeed transition, which for us is driven fron the FMC , but clearly in this case I was wrong?
Thanks.
My guess is that you were already above 250kts when you were at M0.84?
In this case, ATC would expect you to forget about Mach no. and slow to 250 kts immediately. When ATC give an IAS 'on conversion', they assume that you will accelerate to that speed as you descend at fixed Mach and then maintain it.
If you had said something like, "we currently have 270kts indicated; would you like us to reduce to 250 now?" then ATC would probably have confirmed that. If 250 is too slow for you at that altitude, just tell them.
BTW, the phrase, "on transition" in this context was replaced some years ago with, "on conversion", to avoid confusion with transition altitude.
In this case, ATC would expect you to forget about Mach no. and slow to 250 kts immediately. When ATC give an IAS 'on conversion', they assume that you will accelerate to that speed as you descend at fixed Mach and then maintain it.
If you had said something like, "we currently have 270kts indicated; would you like us to reduce to 250 now?" then ATC would probably have confirmed that. If 250 is too slow for you at that altitude, just tell them.
BTW, the phrase, "on transition" in this context was replaced some years ago with, "on conversion", to avoid confusion with transition altitude.
Last edited by eckhard; 8th Jun 2017 at 17:09. Reason: Transition/conversion
Join Date: Jan 2011
Location: Earthville
Posts: 49
Likes: 0
Received 0 Likes
on
0 Posts
As eckhard says, 'on transition' was replaced with 'on conversion' a while back, however a lot of UK controllers will still use 'on transition' (old habits die hard...like some will still use millibars instead of hectopascals).
Anyhow. There is a lot of misinformation amongst controllers about when a/c are flying on what speed. I imagine what happened here is the controller wanted you to fly 250kts when you converted from flying on a Mach Number. We are taught that is usually around FL290 when descending however understand that it can vary greatly depending on a/c type/FMC and profiles etc. Therefore impossible for us to know when you will convert. In the UK we can see what IAS you are flying from the Mode S, however it does not show what that is as a Mach Number and which you are currently flying. So it's very difficult for us to know if you have converted or not.
In the future just say to the controller that you haven't converted to IAS yet and will do when you convert. Or if you're able to fly the IAS straight away then do so as this will show on the Mode S.
Hope that makes sense.
Anyhow. There is a lot of misinformation amongst controllers about when a/c are flying on what speed. I imagine what happened here is the controller wanted you to fly 250kts when you converted from flying on a Mach Number. We are taught that is usually around FL290 when descending however understand that it can vary greatly depending on a/c type/FMC and profiles etc. Therefore impossible for us to know when you will convert. In the UK we can see what IAS you are flying from the Mode S, however it does not show what that is as a Mach Number and which you are currently flying. So it's very difficult for us to know if you have converted or not.
In the future just say to the controller that you haven't converted to IAS yet and will do when you convert. Or if you're able to fly the IAS straight away then do so as this will show on the Mode S.
Hope that makes sense.
Join Date: Mar 2001
Location: etha
Posts: 300
Likes: 0
Received 0 Likes
on
0 Posts
If you have been given speed 250kts or less, then I would imagine that a delay would have also been passed so why would you want to accelerate to 300kts+ before coming back on the speed? There is a debate about whether ATC can give aircraft an indicated speed to transition at rather than allowing the aircraft to automatically convert at whatever altitude it desires, however there are obvious arguments against (brick walls). I don't mind aircraft accelerating beyond the speed I have issued, I just hope that the extended mileage it then accrues from a couple of rather harsh turns isn't minded either.
Thread Starter
Join Date: Oct 1999
Posts: 222
Likes: 0
Received 0 Likes
on
0 Posts
Thanks Guys
Maybe 250 "as soon as you can" is a better way of putting it - the mach/speed transition is very variable dependent on type.
With regards to delay ... theres another conundrum - this was due LGW delays - the next controller gave us direct MAY and LGW a base leg for 26L - hey I know its dynamic, but there you go!
I was surprised, I have been operating into LGW for nearly 30 years and it was the first time I have be "rebuked". The 787 is a very different beast and Im not sure that ATC have got their collective head(s) around the way it works.
Bring back the jumpseat rides .....
Maybe 250 "as soon as you can" is a better way of putting it - the mach/speed transition is very variable dependent on type.
With regards to delay ... theres another conundrum - this was due LGW delays - the next controller gave us direct MAY and LGW a base leg for 26L - hey I know its dynamic, but there you go!
I was surprised, I have been operating into LGW for nearly 30 years and it was the first time I have be "rebuked". The 787 is a very different beast and Im not sure that ATC have got their collective head(s) around the way it works.
Bring back the jumpseat rides .....
Join Date: Jan 2011
Location: Earthville
Posts: 49
Likes: 0
Received 0 Likes
on
0 Posts
If it's a speed for delay then personally I often just say 'when able to make the level restrictions, bring it back to 250kts'. Bit trickier if you're in the middle of a stream of inbounds however.
Expect to be given 250kts due to Gatwick delays an awful lot more in the future. I believe there are plans to bring in the same system as is currently used at Heathrow where aircraft are slowed down in the descent in order to minimise holding. Whether the adjacent ANSP's will be slowing Gatwick traffic down in the cruise for delay as they currently do for Heathrow I'm not sure, however definitely expect it on first contact with London soon.
P.S. I'd love a jumpseat ride in a 787!
Conversely, have you ever been down to Swanwick to see how it works from the other end? Definitely worth a visit...
Expect to be given 250kts due to Gatwick delays an awful lot more in the future. I believe there are plans to bring in the same system as is currently used at Heathrow where aircraft are slowed down in the descent in order to minimise holding. Whether the adjacent ANSP's will be slowing Gatwick traffic down in the cruise for delay as they currently do for Heathrow I'm not sure, however definitely expect it on first contact with London soon.
P.S. I'd love a jumpseat ride in a 787!
Conversely, have you ever been down to Swanwick to see how it works from the other end? Definitely worth a visit...
Join Date: Aug 2009
Location: -
Posts: 39
Likes: 0
Received 0 Likes
on
0 Posts
I believe there are plans to bring in the same system as is currently used at Heathrow where aircraft are slowed down in the descent in order to minimise holding. Whether the adjacent ANSP's will be slowing Gatwick traffic down in the cruise for delay as they currently do for Heathrow I'm not sure, however definitely expect it on first contact with London soon.
For many operators "as soon as you can" equates to "whenever you feel like it".
For the benefit of controllers everywhere and those of us who fly normal aeroplanes, can you please elaborate on what you mean by that statement? I'd certainly like to know how "very different" it is.
t-bag: Not wishing to be controversial but in my experience (737, 747, A320, 787) they all behave pretty much the same in the descent. Sure, the FMC/FMGC and autopilot behaviour may vary but aerodynamically they are all heavy, swept-wing jets; they will go down or slow down, but not at the same time.
Whether 250KIAS in the descent is achievable at e.g.FL350 is another question. IIRC, all except the 747 should be capable of it.
If the FMC/FMGC speed schedule is preventing or delaying compliance with an ATC request, you can always use 'FLCH' or 'Open Descent'. That way you can control the speed manually.
Whether 250KIAS in the descent is achievable at e.g.FL350 is another question. IIRC, all except the 747 should be capable of it.
If the FMC/FMGC speed schedule is preventing or delaying compliance with an ATC request, you can always use 'FLCH' or 'Open Descent'. That way you can control the speed manually.
Thread Starter
Join Date: Oct 1999
Posts: 222
Likes: 0
Received 0 Likes
on
0 Posts
Eckhard - completley agree, 250 KTS is achievable, but from where we were it wasnt "instant" as we allowed the FMC to manage the transition in VNAV, hence my question above - if the controller wanted a more immediate response there are, as you know, other options that we could have used.
Re the 787 on short haul european work we are normally at higher levels (410+) and cruising at M84/85, it also descends on a much shallower profile than other Boeings I have flown ,so yes it is different- fitting us into the lower traffic in the descent seems to be a bit of a headache.
Re the 787 on short haul european work we are normally at higher levels (410+) and cruising at M84/85, it also descends on a much shallower profile than other Boeings I have flown ,so yes it is different- fitting us into the lower traffic in the descent seems to be a bit of a headache.
Re the 787 on short haul european work we are normally at higher levels (410+) and cruising at M84/85, it also descends on a much shallower profile than other Boeings I have flown ,so yes it is different
Had something similar recently. Still in the cruise and informed delays into LGW. Asked to slow down to 250 and to expect some holding. Replied we would slow down immediately to min speed and then 250 when able. Controller was ok with that.
Saved about 5 minutes with the speed reduction but still given the opportunity to admire the Sussex countryside for about ten minutes! Pretty rare to hold but from comments above perhaps it'll become the norm. As an aside always a pleasure to work U.K. ATC. Thanks guys.
Saved about 5 minutes with the speed reduction but still given the opportunity to admire the Sussex countryside for about ten minutes! Pretty rare to hold but from comments above perhaps it'll become the norm. As an aside always a pleasure to work U.K. ATC. Thanks guys.
Had something similar recently. Still in the cruise and informed delays into LGW. Asked to slow down to 250 and to expect some holding. Replied we would slow down immediately to min speed and then 250 when able. Controller was ok with that.
Saved about 5 minutes with the speed reduction but still given the opportunity to admire the Sussex countryside for about ten minutes! Pretty rare to hold but from comments above perhaps it'll become the norm. As an aside always a pleasure to work U.K. ATC. Thanks guys.
Saved about 5 minutes with the speed reduction but still given the opportunity to admire the Sussex countryside for about ten minutes! Pretty rare to hold but from comments above perhaps it'll become the norm. As an aside always a pleasure to work U.K. ATC. Thanks guys.
Join Date: Jul 2000
Location: My views - Not my employer!
Posts: 1,031
Likes: 0
Received 0 Likes
on
0 Posts
Tbag...
If they want 250kt, then FLCH is your friend. VNAV Follows the path at the expense of speed control, so if it rides fast, you end up not following the clearance...
If they want 250kt, then FLCH is your friend. VNAV Follows the path at the expense of speed control, so if it rides fast, you end up not following the clearance...
Thread Starter
Join Date: Oct 1999
Posts: 222
Likes: 0
Received 0 Likes
on
0 Posts
Cough
Doh, I give up, yes I know how the aeroplane works.
What is the title of the thread -250 "on transition" not 250 now?
Thanks to those of you that made sensible contributions.
Doh, I give up, yes I know how the aeroplane works.
What is the title of the thread -250 "on transition" not 250 now?
Thanks to those of you that made sensible contributions.
Join Date: Oct 2007
Location: not the W.P.
Age: 70
Posts: 50
Likes: 0
Received 0 Likes
on
0 Posts
From an old git-
On transition was used by AC CLN as a means of applying, but not actually applying in some cases, separation to streamed aircraft. They could then transfer the aircraft ASAP to TC East but not entirely confirming that they would both be flying at the same speed. I personally gave up ringing CLN to inform them that the following aircraft was actually flying faster and had they ever read the section about separation being 'constant or increasing'.
Parallel headings-Always fails safe.
On transition was used by AC CLN as a means of applying, but not actually applying in some cases, separation to streamed aircraft. They could then transfer the aircraft ASAP to TC East but not entirely confirming that they would both be flying at the same speed. I personally gave up ringing CLN to inform them that the following aircraft was actually flying faster and had they ever read the section about separation being 'constant or increasing'.
Parallel headings-Always fails safe.
What is the title of the thread -250 "on transition" not 250 now?
If you like, It's the reverse of the climb schedule, e.g. 320/M0.85, where after conversion to mach, the IAS reduces from 320 as you climb.
Going back to descent, if ATC asked you to "maintain 320kts after conversion" there would be no real issue as your current IAS would in all likelihood be less than 320. The problem with the FMC arises when 250kts is slower than the current IAS at top of descent.
So, it's not that we think 'you don't know how the aeroplane works', but rather that you might not know what ATC want?
All offered with the highest respect and in the spirit of constructive debriefing!
