New Policies at EK (The Green Dot Thread)
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Zomp
As I stated ".....more or less" -> GD, minimum drag, Vcl or Vm(manoevering) are not absolutely the same, however per aerodynamical law and definition they come up more or less the same. They are all +/- 1.3 of Vs with no limits on bank. Most manufacturers and operators only recommend flying below these speeds with T/O, CLB or MCT power settings. These V2 speeds are somewhat bank limited due to the very reason of beeing closer to Vmin, Vls or Vs whatever you want to call them.
As I stated ".....more or less" -> GD, minimum drag, Vcl or Vm(manoevering) are not absolutely the same, however per aerodynamical law and definition they come up more or less the same. They are all +/- 1.3 of Vs with no limits on bank. Most manufacturers and operators only recommend flying below these speeds with T/O, CLB or MCT power settings. These V2 speeds are somewhat bank limited due to the very reason of beeing closer to Vmin, Vls or Vs whatever you want to call them.
Last edited by chinawladi; 25th Jun 2006 at 10:59.
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Am I right in saying that after take off, you must wait for a positive trend in speed before selecting the next higher flap setting?
You don't deliberately fly below the flap speed for any length of time.
You don't deliberately fly below the flap speed for any length of time.
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Quite right, I believe there should be no confusion between flying below GD speed near the ground with engines at idle thrust during approach and flying at
V2+10 or greater with engine(s) on MCT or TOGA thrust at Take Off.
As break dancer said:"You don't deliberately fly below the flap speed for any length of time."
Next time, at or close Max TOW, when you retract your CONF 1+F, see what the V/S does, because of reduced "stall" margin: very scary close to ground.
Back to the original post, I see quite a lot of guys on the left seat pushing you to do things they are unable to demonstrate or accomplish. Back with my current airline the first sector is "always the captain's sector", which initially irritated me, but now I really kind of like it, 'cause I see what's the jockey on the left seat worth from the outset and if I might learn something from him
Happy landings.
V2+10 or greater with engine(s) on MCT or TOGA thrust at Take Off.
As break dancer said:"You don't deliberately fly below the flap speed for any length of time."
Next time, at or close Max TOW, when you retract your CONF 1+F, see what the V/S does, because of reduced "stall" margin: very scary close to ground.
Back to the original post, I see quite a lot of guys on the left seat pushing you to do things they are unable to demonstrate or accomplish. Back with my current airline the first sector is "always the captain's sector", which initially irritated me, but now I really kind of like it, 'cause I see what's the jockey on the left seat worth from the outset and if I might learn something from him
Happy landings.
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Chin,
Not true mate. In an Airbus, Vls clean is 1.23xVs and at 10k and 200 tons that would be 192kts. Green dot under those same conditions would be.......227kts.
Yep, Green Dot is just the Clean maneuvring speed and is set at 1.45Vs. So when you were flying around in the 'Ludmobile' at 1.3Vs you were actually .15 below Green Dot, so Green Dot is providing us with a 23kt buffer over your suggested limits, at the said conditions.
Vls is a different matter, it ensures 1.23Vs when clean but that drops to only 1.13Vs when you have flap out and are taking off. Your comments about power settings close to Vls are certainly appropriate on take off.
The bottom line is that it seems to be you are slamming a guy for flying below Green Dot but above Vls which is where you spent most of your career. Top tip, if you want to provide some sage advice about FBW aircraft, before you go wading in make sure you know what the speeds actually mean.
I have absolutely no problem with a guy flying below Green Dot as long as he doesn't need to maneuvre the aircraft significantly and stays well clear of Vls. Out of interest, on the approach with full flap selected we routinely decay the speed to Vls+5 with idle power selected and the protection afforded there is still more than 15% below the clean situation decried above.
Schnowzer
Not true mate. In an Airbus, Vls clean is 1.23xVs and at 10k and 200 tons that would be 192kts. Green dot under those same conditions would be.......227kts.
Yep, Green Dot is just the Clean maneuvring speed and is set at 1.45Vs. So when you were flying around in the 'Ludmobile' at 1.3Vs you were actually .15 below Green Dot, so Green Dot is providing us with a 23kt buffer over your suggested limits, at the said conditions.
Vls is a different matter, it ensures 1.23Vs when clean but that drops to only 1.13Vs when you have flap out and are taking off. Your comments about power settings close to Vls are certainly appropriate on take off.
There is very little reason to fly too close to min speed, you trade margin and pax comfort (att) for just a little show off of knowledge of AOM's but lack of airmenship.
I have absolutely no problem with a guy flying below Green Dot as long as he doesn't need to maneuvre the aircraft significantly and stays well clear of Vls. Out of interest, on the approach with full flap selected we routinely decay the speed to Vls+5 with idle power selected and the protection afforded there is still more than 15% below the clean situation decried above.
Schnowzer
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You are absolutely, certainly, positively right mate. Give me at least credit having said "more or less"....... or +/-.
The general idea is to fly with a appropriate margin and that it's poor airmenship to fly too close to min speeds. I was referring to manoevering speeds versus minimum (selectable) speeds.
If you state "I have absolutely no problem with a guy flying below Green Dot as long as he doesn't need to maneuvre the aircraft significantly" then you have to allow the question just WHAT are you doing if NOT manoevering when you fly such speeds................
If its for Vls+5 at Flaps 50, then you are on the final approach path and again bank and v/s limited (stall limited), allowing you to fly closer to min speeds.
The slamming was for the rather silly answer to ones post stating "give me a good reason to fly below GD" which said ".. give me a good reason not to". Sounds like "give me a good reason not to use full lenght".
The general idea is to fly with a appropriate margin and that it's poor airmenship to fly too close to min speeds. I was referring to manoevering speeds versus minimum (selectable) speeds.
If you state "I have absolutely no problem with a guy flying below Green Dot as long as he doesn't need to maneuvre the aircraft significantly" then you have to allow the question just WHAT are you doing if NOT manoevering when you fly such speeds................
If its for Vls+5 at Flaps 50, then you are on the final approach path and again bank and v/s limited (stall limited), allowing you to fly closer to min speeds.
The slamming was for the rather silly answer to ones post stating "give me a good reason to fly below GD" which said ".. give me a good reason not to". Sounds like "give me a good reason not to use full lenght".
I am guessing you are from Austria are you Zomp?
Don
Don
Well who wudda guessed!!!! No wonder there are no Kangaroos in Austria
Don
Don
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Just as a matter of interest Grumpy, where in the manuals did you find we can fly below gd? Do you often try to turn off the fuel pumps of an engine in flight? Ab doesn't mention it in the books neither. This is just common sense, which I obviously doubt you have any!
Thanks for your comments anyway, just wondering how you ever got into the LHS.
Thanks for your comments anyway, just wondering how you ever got into the LHS.
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Gents, all quite simple... Must agree for most part wirh schnowzer.
No problem flying below GD, as long as you stay out of trouble, which is avoiding the VLS.
When would you do it? For example on an extended downwind where control asks you to reduce to below your green dot. Instead of getting the drag already out (an make it uncomfy for the pax with only slats out.. lol), you could just reduce to green dot. The moment you get your base turn, you get your flaps out and start turning... In my opinion that's great airmanship.
About the comment that nothing is written in the book and the fuel pumps etc etc...
When you switch off a fuel pump you'll get a light that says OFF, while airbus has a dark cockpit concept.. on the other hand, nothing prevents you from vlying below GD, even the AP will do it in selected mode. It gets dangerous near VLS, so that's where they built the protection, hence the name VLS.
MR8
No problem flying below GD, as long as you stay out of trouble, which is avoiding the VLS.
When would you do it? For example on an extended downwind where control asks you to reduce to below your green dot. Instead of getting the drag already out (an make it uncomfy for the pax with only slats out.. lol), you could just reduce to green dot. The moment you get your base turn, you get your flaps out and start turning... In my opinion that's great airmanship.
About the comment that nothing is written in the book and the fuel pumps etc etc...
When you switch off a fuel pump you'll get a light that says OFF, while airbus has a dark cockpit concept.. on the other hand, nothing prevents you from vlying below GD, even the AP will do it in selected mode. It gets dangerous near VLS, so that's where they built the protection, hence the name VLS.
MR8
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GD is optimum clean speed, not lowest...
The whole purpose of managed mode is that it manages the profiles and the speeds to be optimum. For example, if you change the cost index, all the speeds will change.
Now, if you fly an approach completely managed (which is almost impossible because of ATC restrictions), the aircraft will fly a continuous descent up to the 'D'-point, where it will automatically activate the approach fase and start decelerating towards final approach speed if you select flaps, which you better do or you will end up hot and high.
If we don't follow the profile because of radar vectors, and we activate the approach fase early, the managed mode will come back to an OPTIMUM speed, which happens to be minimum drag speed (same happens in the holding pattern) and thus GD. There is absolutely no reason for a managed speed to go below the green dot.
We as pilots on the other hand might have reasons to go below green dot, like ATC requests on extended downwinds. And although it is below the OPTIMUM (GD), it is still better then the alternative, which is extending the slats.
MR8
Now, if you fly an approach completely managed (which is almost impossible because of ATC restrictions), the aircraft will fly a continuous descent up to the 'D'-point, where it will automatically activate the approach fase and start decelerating towards final approach speed if you select flaps, which you better do or you will end up hot and high.
If we don't follow the profile because of radar vectors, and we activate the approach fase early, the managed mode will come back to an OPTIMUM speed, which happens to be minimum drag speed (same happens in the holding pattern) and thus GD. There is absolutely no reason for a managed speed to go below the green dot.
We as pilots on the other hand might have reasons to go below green dot, like ATC requests on extended downwinds. And although it is below the OPTIMUM (GD), it is still better then the alternative, which is extending the slats.
MR8
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It is good to read the comments of others who are practical and apply good airmanship to a given situation. It is equally bad but not surprising to read the comments of others who merely resort to insults and personal attacks if their views are not the same as other contributors. It's easy to be rude and insulting on an anonymous forum; very brave. Take what you will out of the original post; perhaps there may be one item that provides food for thought. (p.s. "phase")
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My 2 cents:
GD is not a safe speed but a minimum drag speed. But in my opinion there is no valid reason to go below GD. Slats are mainly produceing lift with a minimum amount of drag. If you can get a grip on AB drag graph you'll see that flying 10kt below GD produces about the same amount of drag as flying the same speed with slats out.
But there is another component to that. Although GD is not a safe speed, flying at or above protects you COMFORTABLY in any case. Try to fly at GD with the speed breakes out and do a 30 deg bank turn and you'll see that VLS is is about 1 or 2 kts below GD. So no major action needed by the engines. That is what really scares the pax and not the pitch build up by extending slats.
Conclusion:
It is perfectly safe to fly below GD but there is no need to and is therefor not recommended by the manufacturer.
Do not compare an AB with what you have learned on a conventional aircraft. GD is not minimum clean speed. But there is still reason not to fly below, although it's not a safety issue.
You safe more fuel with a decent desent planning than with flying below GD and THIS is a real issue within EK crews.
GD is not a safe speed but a minimum drag speed. But in my opinion there is no valid reason to go below GD. Slats are mainly produceing lift with a minimum amount of drag. If you can get a grip on AB drag graph you'll see that flying 10kt below GD produces about the same amount of drag as flying the same speed with slats out.
But there is another component to that. Although GD is not a safe speed, flying at or above protects you COMFORTABLY in any case. Try to fly at GD with the speed breakes out and do a 30 deg bank turn and you'll see that VLS is is about 1 or 2 kts below GD. So no major action needed by the engines. That is what really scares the pax and not the pitch build up by extending slats.
Conclusion:
It is perfectly safe to fly below GD but there is no need to and is therefor not recommended by the manufacturer.
Do not compare an AB with what you have learned on a conventional aircraft. GD is not minimum clean speed. But there is still reason not to fly below, although it's not a safety issue.
You safe more fuel with a decent desent planning than with flying below GD and THIS is a real issue within EK crews.
Last edited by what_goes_up; 30th Jun 2006 at 16:40.
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WGU,
The speedbrake issue has nothing to do with Green Dot. If you leave the speedbrake out in many configurations it is possible to force the aircraft into Vls without turning at all. You have just removed lift from the wing so the min speed has increased. I think that argument is a red herring, we often have to modulate the amount of speedbrake selected to keep above Vls.
Icare, being trite the logical conclusion is that we must descend on the arrow. If the FMS says decelerate, we must decelerate. If we are above the FMS calculated vertical profile we must use speedbrake to achieve it even though we know it is incorrectly calculated.
It does not say in the manuals that we should put out the wheels before the flaps but sometimes going to Moscow you have to do it. Flying below Green Dot is an alternative just like selecting Flap 2, Gear down and flying at 180kts to get down to platform rather than decelerating and descending, which never seems to work as well. Surely (Don't call me Shirley) as pilots, it is our job to apply airmanship to come up with an appropriate solution in any given circumstances from a range of options.
The actual definition of Green Dot may surprise you, it is the 'Engine Out Operating Speed in the Clean Configuration' which also corresponds to the best lift to drag. It would therefore seem to be pretty stupid to fly below it with full power on but in a descent at idle it may well not be the worst thing to do. Interestingly though during clean up on take off we do fly below it with full bore on the jet every day. Worth thinking about?
The speedbrake issue has nothing to do with Green Dot. If you leave the speedbrake out in many configurations it is possible to force the aircraft into Vls without turning at all. You have just removed lift from the wing so the min speed has increased. I think that argument is a red herring, we often have to modulate the amount of speedbrake selected to keep above Vls.
Icare, being trite the logical conclusion is that we must descend on the arrow. If the FMS says decelerate, we must decelerate. If we are above the FMS calculated vertical profile we must use speedbrake to achieve it even though we know it is incorrectly calculated.
It does not say in the manuals that we should put out the wheels before the flaps but sometimes going to Moscow you have to do it. Flying below Green Dot is an alternative just like selecting Flap 2, Gear down and flying at 180kts to get down to platform rather than decelerating and descending, which never seems to work as well. Surely (Don't call me Shirley) as pilots, it is our job to apply airmanship to come up with an appropriate solution in any given circumstances from a range of options.
The actual definition of Green Dot may surprise you, it is the 'Engine Out Operating Speed in the Clean Configuration' which also corresponds to the best lift to drag. It would therefore seem to be pretty stupid to fly below it with full power on but in a descent at idle it may well not be the worst thing to do. Interestingly though during clean up on take off we do fly below it with full bore on the jet every day. Worth thinking about?
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Wow this is a really exciting topic.
Come on!!!! There must be something more important to discuss.
If you can hack it do it if not don’t. If your captain doesn’t want you to do it because of some odd reason then don’t. Who cares.
If you people had had just a little excitement in your previous flying career before joining this circus you would not give a rat’s @ss.
Come on!!!! There must be something more important to discuss.
If you can hack it do it if not don’t. If your captain doesn’t want you to do it because of some odd reason then don’t. Who cares.
If you people had had just a little excitement in your previous flying career before joining this circus you would not give a rat’s @ss.
