Noise abatement

[lederhosen]

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?

[Denti]

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.

[Gulfstream757]

At 1500ft there would be a reduction in power to climb thrust would there not?Sorry if I've understood incorrectly.

[lederhosen]

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]

@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.

[Gulfstream757]

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.

[Gulfstream757]

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.

[Pub User]

I'm a bit confused here.

The FMC will automaticaly select a corresponding climb thrust which should be the same or higher than the reduced take off thrust,

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:

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.

Please explain in language suitable for someone who is halfway down his second bottle of red .. (days off!!) ..

Thanks

[lederhosen]

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.

[Denti]

@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.

[lederhosen]

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.

[mutt]

Automatic climb thrust selection is supposed to select a climb thrust which should be the same or lower than take off thrust The A300-600 was the first aircraft where we encountered increasing thrust at acceleration height, Airbus solved this by limiting the thrust reduction to 25% OR CLIMB THRUST, I'm pretty sure that Embraer does the same thing.

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 Strange combination :)

the point that the aircraft reaches 35 feet will be much closer to the departure end of the runway. True

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. True, (aircraft dependent)

I am also not getting any real benefit from the improved climb You are not getting any benefit as you are trading the increased weight associated with the improved climb for lower thrust settings.

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 And if you combine this with improved climb you will get an even better result.

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.

[haughtney1]

That is indeed an anomaly. The lowest allowable climb thrust is above the thrust we regularly use for takeoff.

http://www.youtube.com/watch?v=y1bDteQ1RsQ

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:ok:

[lederhosen]

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.

[Denti]

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.

[mutt]

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. IN both cases you are achieving 2.4% gradient, normally with an improved climb gradient you would get a higher gradient, but you have traded this for thrust reduction, therefore the flight paths will not cross.

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

[Denti]

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.

[mutt]

our EFB doesn't support that though Are you sure? I believe that you are using LIDO? The performance options are set by the operator in the administration section. You can get your company to reset the parameters. We looked at LIDO couple years ago, they gave us that option, so I presume its for all units and not unique to us.

Mutt

[lederhosen]

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.

[mutt]

could explain why our current procedure makes sense from a noise point of view It doesnt make sense from a noise point of view :)

Mutt

[Denti]

Are you sure? I believe that you are using LIDO

We do use LIDO, however only for charting, obstacle data and operational flight planning. Not for performance calculation, although the performance tool uses the LIDO obstacle data of course. Our performance EFB tool on the boeing is a tui frontend and boeing calculation solution.

[Annex14]

Gentlemen, untill now this has primarily been a pilots discussion. However let me add a bit to this discussion from the experience of an "Dinosauer" that once has spent 8 frustrating year in what is called "Noise Abatement and Environmental Protection ".
Before I go to the approach or departure noise problems let me quote an important sentence from ICAO PANS OPS Doc 8168 - Vol I - Chap V - Noise Abatement Procedures:
Nothing in these procedures shall prevent the pilot-in-command from exercising his authority for the safe operation of his aeroplane.

That sentence in mind I can assure you that taking off in a reduced power procedure will make you the "darling" of the beancounters in your company because of reduced fuel burn and wear on the costly engines. Also you´ll become the darling of the Rabbits on the airport because of 2 or 3 db less perceived noise, but that´s it!!
All the good intentions are gone once you or you FMC or what so ever gadget used applies climb power beyond the airport fence. One should remember what once a Scientist said. Aircraft noise is also perceived via the eyes, means the noise source you see you will hear more intensive. Also as mentioned in this thread social structure of the airport neighbours plays a major role in the amount of noise protests!!
On top of this remark - noise distribution in free atmosphere is a somewhat strange thing to happen. If an ideal atmosphere would exist at the moment of take off, the distribution of noise underneath the flightpath of an aircraft follows an "Gaussian Bell Distribution". Unfortunately there is wind, sometimes cloud layers and / or temperature layers / inversions. The wind will drift the noise in worst case towards one side of the flightpath, the clouds or temperature layers work as a mirror.
I remember evaluations done in the early 80´s at FRA that showed some departures to be extremly noisy while flying excactly on centreline of a SID and passing through a noise monitoring gate - two Noise microphones right and left of the centre line.
This all together can have as a result, that though a pilot has done everything he can do to contribute to noise abatement, the perceived noise level at the airport neighbours house or property becomes uncomfortable, to say the least.

As for the noise generated on an approach, I remember a discussion I had in 1984 with some engineers at Boeing Everett plant. They claimed than already that approach noise will become primarily Aerodynamic Noise, not engine noise.
This said, this is the explanation why Continous Descend Approaches work very well in a distance to the airport fence, but will not have a similar influence on the noise levels on final with gear, flaps and slats extended.
So all you as a pilots involved can do is to follow the SOP´s and try your best. Don´t expect to receive a glorious appreciation fromthe airport neighbours!!
Jo

[Denti]

Interesting that you should mention Germany too. The last time I looked in our Jeppessen rule book, in the ATC differences section it stated that NADP1 should be used for all german airports.


That is true for Annex 16 chapter 2 certified aircraft. Annex 16 chapter 3 certified aircraft can use NADP 2 and apparently there is a loophole that allows acceleration at 1000ft as well. Might be one of those LBA special approvals though, that would be nothing new.

[lederhosen]

Thanks for everyone's input including those via private mail. I am particularly interested how others determine takeoff N1 setting and V speeds and how climb gradients required by particular SIDs are taken account of. Ryanair apparently do not use improved climb. So it seems like they share Mutt's view.

I think it fair to say that this has been a bit of an eye opener. If I lived close to Schönefeld, which a lot of my colleagues do, I would be concerned that everything really is being done to minimize noise when it finally gets going.

[despegue]

As far as I know, and our company policy, is that all German airports have the following noise abatement procedure:

T/o thrust V2 plus 10 min. Until 1500'agl
Then climb thrust and accelerate to flap up speed on schedule.

I am now confused as some German airlines don't seem to comply with this rule themselves? is our company wrong and our info incorrect?

[Annex14]

Nothing to worry about or to be confused. Your company simply flys according
ICAO PANS OPS Doc 8168 Vol I - Part V - Chap. 3.1.2.1 - Procedure A.
That was tested repeatedly on different airports in Germany back in the 80´s, also the Procedure B was checked. However the differences - max 1 - 3 db perceived noise level - are not considered to be significant enough to recommend only one of the two ICAO procedures, or probably any specific type or company related procedure.
As mutt pointed out earlier very correct, the best method of noise abatement is to get as much distance possible between your aircraft and the recepient on the ground.
Jo

[lederhosen]

Things have changed a bit over the last 20 years. The vast majority of takeoffs are now twin jets, which as has been pointed out are most often limited by the 2.4% climb gradient engine out scenario in the second segment. But in almost all cases we have such a surplus of thrust that we see pretty healthy initial climb rates once we finally get airborne.

The noise per aircraft has obviously reduced over time. But overall number of takeoffs has also increased dramatically. The question is could we do better? Ironically I can find no evidence that reduced thrust takeoffs save fuel, nor can I find any conclusive proof that they are noise optimized at least at low weights with low acceleration heights. What they definitely do is make engines last longer as the recent post about the TUI 737 engine record shows. It depends who the engine belongs to as to who benefits from that long term.

[captplaystation]

Annex14, ref your post #22, as you stated, on approach aerodynamic noise is the killer.

I used to fly for a company that had a limit for geardown @ 3.5nm, sometimes a bit late to use as a target versus limit, and certainly only usable if one was applying the 500' VMC stable appr gate in preference to the 1000' IMC one.

It was always nice when flying a visual to try to leave the gear till that point & be spooling up @ 500 agl if possible just for self satisfaction (to the naysayers who say too late to stabilise I would say, well, a CFM56 is permanently spooled up anyhow, so response is pretty much instantaneous from the artificially high flt idle we have)
I had the good fortune to fly many visuals over the city I lived (no noise abatement/local regs to prohibit it, and I am sure the local tourist board liked it ;) ) following an sms sent from 8000' ft or so to Mrs Playstation to look out.
I always asked afterwards, "was it loud" as we arched gracefully across the centre @ 1500' or so agl in a turn, apparently it wasn't, but on the days when I judged it less well & passed above 1500' but with the gear down it was, I am told, much noisier.
So (and good airmanship does sometimes dictate otherwise) the key to appr noise appears to be the latest practical selection of gear (following a well executed CDA ) On take off I am sure thrust reduction@ 1500 accelerate @ 3000 in reduced climb would be the best, but , the need to save fuel/engines has won the day here in most companies priorities, witness Ryanairs change from NADP1 to 2 as the default choice.

[john_tullamarine]

The A300-600 was the first aircraft where we encountered increasing thrust at acceleration height, Airbus solved this by limiting the thrust reduction to 25% OR CLIMB THRUST, I'm pretty sure that Embraer does the same thing.

As a sideline anecdote .. nothing new here.

Wal Stack (the QF ops eng boss back in REALLY olden times) related a tale concerning the very earliest days of reduced thrust takeoffs (QF was one of the initial leading lights).

Appears one of his 707s launched to wherever ... crew came back and raised the point that, at thrust reduction to climb power, the FE had pushed up the throttles .. and the Commander thought that a tad strange.

Whereupon Wal had a direction issued to limit takeoff thrust reduction to the intended climb thrust setting .. which made the spectre go away and kept his operating crews happy and contented.

One of the advantages of having an (ex) operator running the ops eng show.

[an3_bolt]

crew came back and raised the point that, at thrust reduction to climb power, the FE had pushed up the throttles

...pretty common on the 747 these days - but without the FE. Happens mostly at regional/lower weights. Still feels uncomfortable using a serious amount of runway at lower thrust settings, getting airborne and increasing thrust shortly after......

Haven't seen the FAFC "unlock" shuffle for a while though.........