Jet decent profile question
Thread Starter
Join Date: Apr 2007
Location: Here and Now
Posts: 41
Likes: 0
Received 0 Likes
on
0 Posts
Jet decent profile question
Question for the jet girls and boys. The following is a fairly realistic (yet hypothetical) scenario and i would appreciate some feedback from the jet drivers (B767/B737/A320 etc) as to what they would find reasonable and workable in this (or similar) situation.
3 jets (3 different companys - use your imagination as to who operates which ones) all inbound to the same airport with estimates within 7 minutes of each other. An A320 so far #1 two minutes ahead - on a different track to a B767 (#2). The B737 (#3) on same track as B767 however 2000ft higher.
The enroute controller handling the aircraft prior to approach to this major centre has no radar and thus hands the aircraft off at 150nm rather than the usual which is much closer. The A320 had been given best speed to get him #1 easily (no problem so far). The B737 when advised that he was too close to the preceeding B767 and could possibly expect delays increased from 450kts (or thereabouts) to 540kts (or thereabouts) - it seemed in an effort to get in front of aforementioned B767.
Ok with me so far? The A320 is now far enough ahead as to not cause any great issues. However the nice 10nm gap between the 2 boeings is now approximately 2nm and closing (very unworkable) but the 737 is still 2000ft above. At 150nm the 737 was requested to reduce speed by 30kts. The 737 had no yet commenced descent. The pilot advised the controller that 30kts wasn't possible, however 10kts was ok.
In this (or similar) situation...
a) Would a 30kt reduction at 150nm prior to descent being commenced be a huge problem? Does it depend on the aircraft operator (policy etc)?
b) would the pilot prefer vectors for a 20nm final instead?
c) considering that both aircraft belonged to 2 different companies was the B737 driver just being painful?
The sheer quantity of extra work this lack of airmanship (if the pilot was just being a pain) has the ability to cause is pretty astronomic. A 30kt reduction over 150nm should have given a nice 10nm on final, enough for the preceeding B767 to land/backtrack and vacate. Surely it would make sense to play nice and therefore play safe?
Advice/information from jetdrivers would be greatly appreciated.
Som
3 jets (3 different companys - use your imagination as to who operates which ones) all inbound to the same airport with estimates within 7 minutes of each other. An A320 so far #1 two minutes ahead - on a different track to a B767 (#2). The B737 (#3) on same track as B767 however 2000ft higher.
The enroute controller handling the aircraft prior to approach to this major centre has no radar and thus hands the aircraft off at 150nm rather than the usual which is much closer. The A320 had been given best speed to get him #1 easily (no problem so far). The B737 when advised that he was too close to the preceeding B767 and could possibly expect delays increased from 450kts (or thereabouts) to 540kts (or thereabouts) - it seemed in an effort to get in front of aforementioned B767.
Ok with me so far? The A320 is now far enough ahead as to not cause any great issues. However the nice 10nm gap between the 2 boeings is now approximately 2nm and closing (very unworkable) but the 737 is still 2000ft above. At 150nm the 737 was requested to reduce speed by 30kts. The 737 had no yet commenced descent. The pilot advised the controller that 30kts wasn't possible, however 10kts was ok.
In this (or similar) situation...
a) Would a 30kt reduction at 150nm prior to descent being commenced be a huge problem? Does it depend on the aircraft operator (policy etc)?
b) would the pilot prefer vectors for a 20nm final instead?
c) considering that both aircraft belonged to 2 different companies was the B737 driver just being painful?
The sheer quantity of extra work this lack of airmanship (if the pilot was just being a pain) has the ability to cause is pretty astronomic. A 30kt reduction over 150nm should have given a nice 10nm on final, enough for the preceeding B767 to land/backtrack and vacate. Surely it would make sense to play nice and therefore play safe?
Advice/information from jetdrivers would be greatly appreciated.
Som
It does depend upon altitude and weight, a 30kt reduction at high altitude is probably not possible.
540kts for a 737
must have had a reasonable tailwind.
Bloggs, what are you drinking tonight?
540kts for a 737
must have had a reasonable tailwind.Bloggs, what are you drinking tonight?
The B737 when advised that he was too close to the preceeding B767 and could possibly expect delays increased from 450kts (or thereabouts) to 540kts (or thereabouts)
) 737 crew sped up of their own volition from 450 to 540 to try to beat the 767 and then said they couldn't take a 30kt speed reduction, they are being dickheads. If the 737 is anything like the thing I fly, from normal cruise you can slow down at least 20kts G/S, especially if they've already sped up by 90!The controller should have fixed it all at 150nm-ish by asking everybody's DME/RNAV distance to the field. That would have confirmed the 737 was behind the 767 and that's the way it should have stayed.
Would a 30kt reduction at 150nm prior to descent being commenced be a huge problem?
would the pilot prefer vectors for a 20nm final instead?
If that doesn't work apply a bit of trackstretching later.
Somni,
sounds like the 73, was initially attempting to get ahead of the 76 by his increase in speed. At high altitudes (am assuming it was an NG) there probably wasn't much cruise speed range between Vmax and Vmin - likely 20 knots, so it seems reasonable that 10 knots off was all he could give you without commencing descent. As he descends, he will get more margin and be able to reduce speed further - even worst case extending slat at lower levels. The only way (worst way economically) for significant spacing at high levels would be some extra track miles for such types.
To answer your questions:
a: See above - yes for most types at high altitudes.
b: Preferably not - ecomomics - best to start the speed reduction early such as a requirement to cross a position at a certain time - but give them plenty miles to effect this "RTA".
c: Initially, but he had little choice to slow down unless you got him down say below FL200.
With the price of fuel these days most operators are running low cost indexs ie. they are able to fly faster speeds if needed but not a lot slower (up high)
Hope this helps
WD
sounds like the 73, was initially attempting to get ahead of the 76 by his increase in speed. At high altitudes (am assuming it was an NG) there probably wasn't much cruise speed range between Vmax and Vmin - likely 20 knots, so it seems reasonable that 10 knots off was all he could give you without commencing descent. As he descends, he will get more margin and be able to reduce speed further - even worst case extending slat at lower levels. The only way (worst way economically) for significant spacing at high levels would be some extra track miles for such types.
To answer your questions:
a: See above - yes for most types at high altitudes.
b: Preferably not - ecomomics - best to start the speed reduction early such as a requirement to cross a position at a certain time - but give them plenty miles to effect this "RTA".
c: Initially, but he had little choice to slow down unless you got him down say below FL200.
With the price of fuel these days most operators are running low cost indexs ie. they are able to fly faster speeds if needed but not a lot slower (up high)
Hope this helps
WD
Thread Starter
Join Date: Apr 2007
Location: Here and Now
Posts: 41
Likes: 0
Received 0 Likes
on
0 Posts
opps
Amos you caught me out. Of course my incorrect spelling was a dead give away that I was having you all on!
Thanks to everyone else I wasn't sure whether 30kts was a lot or a little in the greater scheme of things... quite obviously i don't fly the buggers!
Is there much competition between companies as far as trying to get to airfields first in order to not have to be delayed? - stupid question I know, but I like to think of myself as naive enough to think that the pilots are happy to help each other out at times.
If I have screwed up any spelling on this one please forgive me. It is too late to get out the dictionary - don't even mention spellchecker!
Thanks to everyone else I wasn't sure whether 30kts was a lot or a little in the greater scheme of things... quite obviously i don't fly the buggers!
Is there much competition between companies as far as trying to get to airfields first in order to not have to be delayed? - stupid question I know, but I like to think of myself as naive enough to think that the pilots are happy to help each other out at times.
If I have screwed up any spelling on this one please forgive me. It is too late to get out the dictionary - don't even mention spellchecker!
There is no way that any jet aircraft could accelerate from 450 GS to 540 GS in the cruise by cranking up the thrust.
There simply isnt that much margin between high and low speed buffet - unless they were both cruising in the mid twenties.
Sounds like the 737 got a good tailwind - which does happen from time to time.
There simply isnt that much margin between high and low speed buffet - unless they were both cruising in the mid twenties.
Sounds like the 737 got a good tailwind - which does happen from time to time.
Join Date: Feb 2007
Location: 3rd rock from the sun
Posts: 59
Likes: 0
Received 0 Likes
on
0 Posts
Mass X Inertia
Simple physics by dear boy MASS X INERTIA. and the 3 times table comes in handy, add say 10 miles to slow down Bingo.....TWC and WT all add to the equation. But hey, Mr Boeing & Airbus have made it easy.
.
Join Date: Jun 2006
Location: Down a dark hole
Posts: 301
Likes: 0
Received 0 Likes
on
0 Posts
I don't see the problem here.
Just treat the 737 like he was GA.
Centre - XX1234, turn left heading ZZZ, traffic separation for your descent
Send him via Bullamakanka and cost him lots of extra fuel.
R
Just treat the 737 like he was GA.
Centre - XX1234, turn left heading ZZZ, traffic separation for your descent
Send him via Bullamakanka and cost him lots of extra fuel.
R
Join Date: Apr 2002
Location: Australia
Posts: 126
Likes: 0
Received 0 Likes
on
0 Posts
All you rocket scientists forget about wind some time.
A while ago was accused of "speeding up by 50 knots" by BNE CEN when our Mach number and therefore TAS had not changed. We had just turned over a waypoint and picked up extra speed due to an increase in tail wind.
Also the type of 73 and the weight will make a difference. A heavy 800 might only be able to reduce 10 knots while a light one maybe 20 or so.
Just give us a time at the feeder fix, remembering we can be up to one minute early. Vector us if need be, just don't give us the restriction on time or descent speed when we've just commenced the descent.
Tag
A while ago was accused of "speeding up by 50 knots" by BNE CEN when our Mach number and therefore TAS had not changed. We had just turned over a waypoint and picked up extra speed due to an increase in tail wind.
Also the type of 73 and the weight will make a difference. A heavy 800 might only be able to reduce 10 knots while a light one maybe 20 or so.
Just give us a time at the feeder fix, remembering we can be up to one minute early. Vector us if need be, just don't give us the restriction on time or descent speed when we've just commenced the descent.
Tag
Join Date: Sep 2003
Location: In a burrow
Posts: 252
Likes: 0
Received 0 Likes
on
0 Posts
Somn,
You will see there is not much room to slow down, about 20kts would be it.
This is at F370 which is lower than usual for an NG. At higher levels the margin is much smaller, so your 30kt reduction is not going to happen.
I know you said it was a hyperthetical situation, but it didn't take long for blokes (Capn Bloggs) to start calling people d!ckheads, and assuming who the operators would be.
As for a 737 overtaking a 767 by a large margin (and only 2000' higher) - that will never happen unless the 76 is on a big speed reduction.
You will see there is not much room to slow down, about 20kts would be it.
This is at F370 which is lower than usual for an NG. At higher levels the margin is much smaller, so your 30kt reduction is not going to happen.
I know you said it was a hyperthetical situation, but it didn't take long for blokes (Capn Bloggs) to start calling people d!ckheads, and assuming who the operators would be.
As for a 737 overtaking a 767 by a large margin (and only 2000' higher) - that will never happen unless the 76 is on a big speed reduction.
Last edited by Capt Basil Brush; 27th May 2007 at 06:07.
