Noise abatement
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Noise abatement
Anyone else concerned that a procedure where thrust (and noise) is increased at 1500 feet might not comply with the spirit of noise abatement. It is obviously SID dependent, but some late night departures have us also using improved climb and rotating most of the way down 4,000 meter runways.
I have raised this one with our experts and they claim that as we are making less noise by reducing takeoff thrust so much, it does not matter. Is anybody aware of any studies that have been carried out that would back this up and what do other people do?
I have raised this one with our experts and they claim that as we are making less noise by reducing takeoff thrust so much, it does not matter. Is anybody aware of any studies that have been carried out that would back this up and what do other people do?
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Wondered that myself. We changed that procedure around a year back and nowadays use always full climb thrust whenever an unrestricted climb is likely no matter how much we reduced thrust for take off. Additionally we changed our acceleration altitude to 1000ft.
Kinda seems to be not in line with noise abatement in general.
Kinda seems to be not in line with noise abatement in general.
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That is exactly the point Gulfstream, our performance tool now has us using toga N1 often way below climb 2, never mind full climb thrust.
Denti I wonder if there is any link between the big outcry from people around Frankfurt, Munich and SXF and our bean counter's recent attitude towards noise.
The difference in height at the airfield boundary in Munich and therefore presumably noise impact on the good burgers of Halbergmoos is huge if you take out the improved climb (usually same N1 I have found). I appreciate that climb gradient further away is improved as was discussed in some detail a couple of years ago. But the noise impact to those close in seems to have been neatly ignored!
Denti I wonder if there is any link between the big outcry from people around Frankfurt, Munich and SXF and our bean counter's recent attitude towards noise.
The difference in height at the airfield boundary in Munich and therefore presumably noise impact on the good burgers of Halbergmoos is huge if you take out the improved climb (usually same N1 I have found). I appreciate that climb gradient further away is improved as was discussed in some detail a couple of years ago. But the noise impact to those close in seems to have been neatly ignored!
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@Gulfstream757: that depends. We use 1000ft AGL as acceleration altitude anyway, not 1500ft, which moves the point of climb thrust reduction closer to the airport, however closer to the ground as well.
As i fly the 737, and i believe lederhosen does as well, we can user select derates 1 and 2, add assumed temperature to the mix and we can reduce our take off thrust by something around 35 to 40% of the full rated thrust. The FMC will automaticaly select a corresponding climb thrust which should be the same or higher than the reduced take off thrust, but actually quite often is not since climb 2 as lowest climb thrust setting is only a reduction by around 20%. The climb thrust ratings are user selectable as well. Since it is more economical to use full climb thrust to save fuel (shorter time to cruise level) we do that now.
Which means that we will get a huge increase of thrust at acceleration altitude, especially in a lightweight -700. And corresponding to that increase of thrust we will get an increase of noise output.
As i fly the 737, and i believe lederhosen does as well, we can user select derates 1 and 2, add assumed temperature to the mix and we can reduce our take off thrust by something around 35 to 40% of the full rated thrust. The FMC will automaticaly select a corresponding climb thrust which should be the same or higher than the reduced take off thrust, but actually quite often is not since climb 2 as lowest climb thrust setting is only a reduction by around 20%. The climb thrust ratings are user selectable as well. Since it is more economical to use full climb thrust to save fuel (shorter time to cruise level) we do that now.
Which means that we will get a huge increase of thrust at acceleration altitude, especially in a lightweight -700. And corresponding to that increase of thrust we will get an increase of noise output.
Last edited by Denti; 6th Jul 2012 at 16:45. Reason: fingertrouble
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Aah,OK I understand now,as you can see I'm only 14 so please excuse my mistake,with what I now know I agree with you it is against noise abatement,but I guess in the modern world money is the no.1 concern.
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Thanks for the good info,nice to hear from a real 737 pilot,sorry for my lack of knowledgeon the matter,would I be able to send you a private message with a few Q's I have on the 737? I don't want to change the subject of this thread.
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I'm a bit confused here.
That is not as I understand it. I have always seen a thrust REDUCTION upon selection (automatically or otherwise) of climb thrust. Mr Boeing's publication for the 737 has this to say on the matter:
Please explain in language suitable for someone who is halfway down his second bottle of red .. (days off!!) ..
Thanks
The FMC will automaticaly select a corresponding climb thrust which should be the same or higher than the reduced take off thrust,
The FMC automatically selects the highest climb thrust available (CLB, CLB-1, CLB-2) which would not result in a thrust lever push, when the aircraft transitions from takeoff to climb.
Thanks
Thread Starter
That is indeed an anomaly. The lowest allowable climb thrust is above the thrust we regularly use for takeoff. In any case you can always select a higher climb thrust as Denti's airline appears to be doing.
Years ago my company insisted that we increase take off thrust N1 if necessary so as to ensure that it was not below climb thrust. This was fairly rare. When we introduced the EFB it became a regular occurrence and the company line was that as we were reducing noise at takeoff we were still quieter than we would have been.
However it would interest me to know what line Ryanair, Norwegian and other big 737 players are using.
There is plenty of interest in continuous decent approaches (CDA) as noise abatement and cost saving go hand in hand. But using most of the runway and then selecting a higher thrust setting lower down over people close to the airport seems to have escaped notice.
Years ago my company insisted that we increase take off thrust N1 if necessary so as to ensure that it was not below climb thrust. This was fairly rare. When we introduced the EFB it became a regular occurrence and the company line was that as we were reducing noise at takeoff we were still quieter than we would have been.
However it would interest me to know what line Ryanair, Norwegian and other big 737 players are using.
There is plenty of interest in continuous decent approaches (CDA) as noise abatement and cost saving go hand in hand. But using most of the runway and then selecting a higher thrust setting lower down over people close to the airport seems to have escaped notice.
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@Pub User, that sentence was indeed misleading. Automatic climb thrust selection is supposed to select a climb thrust which should be the same or lower than take off thrust, however as lederhosen wrote above that is even with the automatic selection quite often not the case.
With manually selected climb 1 or full climb thrust a thrust increase at "reduction" altitude is a sure thing.
With manually selected climb 1 or full climb thrust a thrust increase at "reduction" altitude is a sure thing.
Thread Starter
From the deafening silence of the experts other than Denti (whose input is as always interesting) it seems that noise abatement does not seem to be of much concern to most people or perhaps somebody can explain why increasing noise at the abatement point is not a problem.
I appreciate this will vary by aircraft type and airport. But assuming a non weight limited 737 departure in the early hours of the morning selecting derate 2, max assumed, improved climb and then accelerating at 1500 feet or lower does not seem to make sense from a noise abatement point of view.
The first segment of the takeoff will take much longer and the point that the aircraft reaches 35 feet will be much closer to the departure end of the runway. The second segment, whilst meeting the 2.4% climb gradient, will be performed at a thrust setting that may be well below minimum climb thrust and will therefore reach acceleration height further away from the airport.
I am also not getting any real benefit from the improved climb as I accelerate at or before the point where the improved climb path crosses the non improved climb path. At this point we increase power and clean up all of which increases the nuisance to those living close in to the airport.
Gut feel would suggest that if I use a takeoff thrust setting equivalent to minimum climb thrust and climb to acceleration height closer to the airport, even possibly climbing to 3000 feet before cleaning up, I will reduce the noise impact to those along the departure path. Again if anybody knows of any studies that throw light on this I would be most grateful.
I appreciate this will vary by aircraft type and airport. But assuming a non weight limited 737 departure in the early hours of the morning selecting derate 2, max assumed, improved climb and then accelerating at 1500 feet or lower does not seem to make sense from a noise abatement point of view.
The first segment of the takeoff will take much longer and the point that the aircraft reaches 35 feet will be much closer to the departure end of the runway. The second segment, whilst meeting the 2.4% climb gradient, will be performed at a thrust setting that may be well below minimum climb thrust and will therefore reach acceleration height further away from the airport.
I am also not getting any real benefit from the improved climb as I accelerate at or before the point where the improved climb path crosses the non improved climb path. At this point we increase power and clean up all of which increases the nuisance to those living close in to the airport.
Gut feel would suggest that if I use a takeoff thrust setting equivalent to minimum climb thrust and climb to acceleration height closer to the airport, even possibly climbing to 3000 feet before cleaning up, I will reduce the noise impact to those along the departure path. Again if anybody knows of any studies that throw light on this I would be most grateful.
Last edited by lederhosen; 7th Jul 2012 at 10:43.
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Automatic climb thrust selection is supposed to select a climb thrust which should be the same or lower than take off thrust
On the 737, I presume that you guys are using Laptops utilizing SCAP compliant software.... but what happens when you just use the FMS, will it give you an assumed temperature lower than climb thrust?
derate 2, max assumed, improved climb
the point that the aircraft reaches 35 feet will be much closer to the departure end of the runway.
will be performed at a thrust setting that may be well below minimum climb thrust and will therefore reach acceleration height further away from the airport.
I am also not getting any real benefit from the improved climb
Gut feel would suggest that if I use a takeoff thrust setting equivalent to minimum climb thrust and climb to acceleration height closer to the airport
Remember that you are concerned about perceived noise levels rather than the amount of noise that you are actually making, so increasing distance from the recipient and limiting the exposure are the keys.
You could try searching the community noise document for the 737, or downloading the Boeing training course on the subject.
Good Luck.
Last edited by mutt; 7th Jul 2012 at 18:24.
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That is indeed an anomaly. The lowest allowable climb thrust is above the thrust we regularly use for takeoff.
Not as unusual as you think. On GE90-115/110 777's on anything longer than about 2800m of runway, the assumed temp is almost always less than climb thrust
Last edited by haughtney1; 7th Jul 2012 at 18:55.
Thread Starter
Thanks for those contributions, I have looked at the references you suggest Mutt. The community noise document is pretty vague, in summary it says noise is a difficult subject to quantify and one should refer to individual operators for more information.
The combination of derate, assumed and improved climb is what our EFB churns out pretty much by default. Previously with paper tables I found it easier to get an overview of what we were doing. Now a small change in a non limiting situation can result in a different flap setting and derate without it being obvious why. The EFB tries to get the lowest takeoff thrust setting for the weight and conditions. The result is what another contributor wittily referred to on another thread as high idle takeoffs. I have seen no evidence that noise is taken into account.
In one of the training courses there is a graph showing the effect of improved climb. It shows clearly from the start of the takeoff run that the point where the improved climb crosses above the unimproved is half way to 3000 feet. Thus my hypothesis that if we speed up at 1500 feet or below there does not seem to be much climb performance benefit and there is a significant increase in noise for the airport's neighbors.
If I have understood Haughtney correctly then the increase in thrust seems to occur on most 777 takeoffs as well, although unless you live at the end of the runway in Dubai you will probably be less concerned by this then by the sheer volume of takeoffs by 737s at most other places.
What has got me thinking is the significant increase in complaints from people living around airports in Germany at a time when traffic has not really increased. The new runway in Frankfurt has led to changes in where planes fly and therefore annoyed people who were previously unaffected. But I wonder if some of the recent operational changes like those mentioned by myself and Denti who flies for the second largest airline here are also contributing.
The combination of derate, assumed and improved climb is what our EFB churns out pretty much by default. Previously with paper tables I found it easier to get an overview of what we were doing. Now a small change in a non limiting situation can result in a different flap setting and derate without it being obvious why. The EFB tries to get the lowest takeoff thrust setting for the weight and conditions. The result is what another contributor wittily referred to on another thread as high idle takeoffs. I have seen no evidence that noise is taken into account.
In one of the training courses there is a graph showing the effect of improved climb. It shows clearly from the start of the takeoff run that the point where the improved climb crosses above the unimproved is half way to 3000 feet. Thus my hypothesis that if we speed up at 1500 feet or below there does not seem to be much climb performance benefit and there is a significant increase in noise for the airport's neighbors.
If I have understood Haughtney correctly then the increase in thrust seems to occur on most 777 takeoffs as well, although unless you live at the end of the runway in Dubai you will probably be less concerned by this then by the sheer volume of takeoffs by 737s at most other places.
What has got me thinking is the significant increase in complaints from people living around airports in Germany at a time when traffic has not really increased. The new runway in Frankfurt has led to changes in where planes fly and therefore annoyed people who were previously unaffected. But I wonder if some of the recent operational changes like those mentioned by myself and Denti who flies for the second largest airline here are also contributing.
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I guess the take off case really never mattered, especially for small jets like the 737 which have a pretty small noise footprint compared to those longhaus planes.
Especially in Frankfurt most noise complaints come from areas affected by the approaches to the new runway. Those areas have in general a higher income bracket population than below the other existing approach paths. As someone who has to work quite a bit below one of new approach paths (VC) the change is a pretty heavy one, not so much inside the building since it is mostly noise proof, but on the deck on the roof (smokers lounge) it is hard to miss.
Especially in Frankfurt most noise complaints come from areas affected by the approaches to the new runway. Those areas have in general a higher income bracket population than below the other existing approach paths. As someone who has to work quite a bit below one of new approach paths (VC) the change is a pretty heavy one, not so much inside the building since it is mostly noise proof, but on the deck on the roof (smokers lounge) it is hard to miss.
Last edited by Denti; 8th Jul 2012 at 07:23.
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In one of the training courses there is a graph showing the effect of improved climb. It shows clearly from the start of the takeoff run that the point where the improved climb crosses above the unimproved is half way to 3000 feet.
Normal V1 may give a V2 at 35 feet and 7000 feet.
Imp Climb may give a V2 at 35 feet and 10000 feet.
From these starting points, draw gradient lines of 2.4% up to acceleration height and you will see that they wont cross. However, if you use improved climb without the additional thrust reduction, they will cross.
Your EFB is only as good as the inputs, garbage in, garbage out.....
Mutt
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Hmm, nice idea, our EFB doesn't support that though. Many of us do not like improved climb though, especially on long runways as it tends to erode any safety margin there is and it is not really fun to start your rotation behind the opposite 1000ft marker with a medium jet.
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our EFB doesn't support that though
Mutt
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I was hoping that someone could explain why our current procedure makes sense from a noise point of view. So far things seem to be going in the opposite direction.
I am interested that only one other current 737 pilot has contributed. Anybody know what Ryanair or even Southwest do (although I accept that is less likely on this forum).
While the noise footprint of a medium jet is a lot smaller than a heavy, there are a lot more of them taking off around 6 in the morning. If you pull more than idle reverse in Palma at that time you get treated like a criminal, but scream past Sant Jordi off the end of 06R possibly selecting 90% N1 at 1000 feet and nobody cares.
I am interested that only one other current 737 pilot has contributed. Anybody know what Ryanair or even Southwest do (although I accept that is less likely on this forum).
While the noise footprint of a medium jet is a lot smaller than a heavy, there are a lot more of them taking off around 6 in the morning. If you pull more than idle reverse in Palma at that time you get treated like a criminal, but scream past Sant Jordi off the end of 06R possibly selecting 90% N1 at 1000 feet and nobody cares.