New Scientist - lining up from 70km out reduces noise (Merged)

[5711N0205W]

From New Scientist, all sorts of implications for all sorts of people, posted here as an illustration of discussions that may affect aircraft ops.

New Scientist Link (http://www.newscientist.com/news/news.jsp?id=ns99994395)

Noise nuisance from aircraft can be reduced significantly by changing the way the planes come in to land. Lining up with the runway as far as 70 kilometres away and making a steady descent can more than halve the acoustic energy that reaches the ground, an international research consortium has found.

Now pressure is on for the technique to be considered for the busiest international airport in the world, Heathrow, in London, UK.

Noise pollution around airports is set to get worse. Air traffic worldwide is increasing at 4.7 per cent per year and is expected to triple by 2030. Without a major initiative to reduce aircraft noise, airports will be prevented from handling the extra flights, says Mike Howse, director of technology and engineering at the British aero-engine maker Rolls-Royce.


Noise-reducing approach
The noise during descent comes from two sources: the engines, particularly when they have to deliver high power as the plane manoeuvres near to the ground, and aerodynamic noise from the flaps on the trailing edge of the wing, which also gets worse during manoeuvres.

So the way to reduce noise near the ground seems straightforward: carry out the manoeuvres needed to get on course for the runway farther away from airports and at high altitude, and then descend slowly with minimal corrections.


Continuous descent


A method of noise reduction along these lines, known as a continuous descent approach, is already in use at many airports. But now a consortium that includes Rolls-Royce, the Massachusetts Institute of Technology, the University of Cambridge, British Airways and the UK Civil Aviation Authority wants to take the idea further.

In a continuous descent approach, an aircraft begins its final descent from a distance of about 17 kilometres and an altitude of 4000 feet. It then maintains a steady 3° angle of descent during its approach, says Richard Wright, spokesman for the UK's National Air Traffic Services.

But this technique involves significant manoeuvring at 4000 feet and below, which can be noisy for people living under that part of the flight path. "What we need is an approach procedure where there are no transients in thrust over noise-sensitive locations," says John-Paul Clarke, an aeronautical engineer at MIT.

Using a flight simulator modified to analyse noise, he and colleagues at Boeing and NASA developed a quieter continuous descent path into Louisville International Airport in Kentucky. Working with the cargo airline UPS, Clarke then asked the crews of two Boeing 767 jets to adopt the new approach routine.


Acoustic energy


Instead of beginning the descent 17 kilometres away, the crew began their descents some 70 kilometres away and from a height of 11,000 feet, while maintaining an angle of descent of 3° and keeping engine power changes to a minimum.

The teams measured the results with 14 microphones placed in neighbourhoods near the airport and found that compared with conventional 767 approaches, the noise dropped by between 3.9 and 6.5 decibels. That is a drop in acoustic energy of more than half, and is noticeable to the human ear.

What is more, the manoeuvre saved nearly 200 kilograms of fuel on each landing, Clarke says. The team has submitted its research to the Journal of Aircraft.



Complex patterns


London is served by five airports whose in and outbound air lanes form complex patterns above the city and require aircraft to manoeuvre at relatively low altitude. Wright says it could be extremely difficult to reorganise the airspace in a way that does not require low-altitude manoeuvres.

But the public may force the issue. John Stewart of the pressure group Heathrow Association for the Control of Aircraft Noise welcomes the idea. "These experiments are worth doing, whatever the challenges," he says.

"It certainly sounds like there is an upside for people living near the airport. We'd need to know what it means for people further out. But the technique should be considered for Heathrow."


Paul Marks

[Pax Vobiscum]

See New Scientist article :Smooth aircraft approach cuts noise pollution (http://www.newscientist.com/news/news.jsp?id=ns99994395)

HACAN are in favour (no surprise there) - I'd be interested in the views of the professionals!

[Shaggy Sheep Driver]

The article seems to stating the bleedin obvious. The aeroplanes will still be very noisy near the ground with high power against the drag of flaps.

It does seem 'a bad thing' to use lots of brute force power in order to bring a heavy object like a jet transport from a high and fast position (start of descent) to a low and slow position (on the runway).

Perhaps glide approaches are the answer? They would be very unforgiving of undershooting (maybe retracting powerful airbrakes, glider-fashion, could be used to 'add energy' rather than spooling up the engines?), so perhaps the approach should be computer controlled - a bit like the Space Shuttle? Something for future, perhaps?

SSD

[Self Loading Freight]

From a press release from New Scientist today:


NOISE nuisance from aircraft can be reduced significantly by changing the way the planes come in to land. Lining up with the runway as far as 70 kilometres away and making a steady descent can more than halve the acoustic energy that reaches the ground, an international research consortium has found. Now pressure is on for the technique to be considered for London's Heathrow, the busiest international airport in the world.

Noise pollution around airports is set to get worse. Air traffic worldwide is increasing at 4.7 per cent per year and is expected to triple by 2030. Without a major initiative to reduce aircraft noise, airports will be prevented from handling the extra flights, says Mike Howse, director of technology and engineering at the British aero- engine maker Rolls-Royce.

The noise during descent comes from two sources: the engines, particularly when they have to deliver high power as the plane manoeuvres near to the ground, and aerodynamic noise from the flaps on the trailing edge of the wing, which also gets worse during manoeuvres. So the way to reduce noise near the ground seems straightforward: carry out the manoeuvres needed to get on course for the runway farther away from airports and at high altitude, and then descend slowly with minimal corrections.

A method of noise reduction along these lines, known as a continuous descent approach, is already in use at many airports. But now a consortium that includes Rolls-Royce, the Massachusetts Institute of Technology, the University of Cambridge, British Airways and the UK Civil Aviation Authority wants to take the idea further.
In a continuous descent approach, an aircraft begins its final descent from a distance of about 17 kilometres and an altitude of 4000 feet. It then maintains a steady 3-degree angle of descent during its approach, says Richard Wright, spokesman for the UK's National Air Traffic Services. But this technique involves significant manoeuvring at 4000 feet and below, which can be noisy for people living under that part of the flight path.

"What we need is an approach procedure where there are no transients in thrust over noise-sensitive locations," says John-Paul Clarke, an aeronautical engineer at MIT.

Using a flight simulator modified to analyse noise, he and colleagues at Boeing and NASA developed a quieter continuous descent path into Louisville International Airport in Kentucky. Working with the cargo airline UPS, Clarke then asked the crews of two Boeing 767 jets to adopt the new approach routine.

Instead of beginning the descent 17 kilometres away, the crew began their descents some 70 kilometres away and from a height of 11,000 feet, while maintaining an angle of descent of 3 degrees and keeping engine power changes to a minimum. The teams measured the results with 14 microphones placed in neighbourhoods near the airport and found that compared with conventional 767 approaches, the noise dropped by between 3.9and 6.5 decibels. That's a drop in acoustic energy of more than half, and is noticeable to the human ear. What's more, the manoeuvre saved nearly 200 kilograms of fuel on each landing, Clarke says.The team has submitted its research to the Journal of Aircraft.

London is served by five airports whose in and outbound air lanes form complex patterns above the city and require aircraft to manoeuvre at relatively low altitude. Wright says it could be extremely difficult to reorganise the airspace in a way that does not require low-altitude manoeuvres.

But the public may force the issue. John Stewart of the pressure group Heathrow Association for the Control of Aircraft Noise welcomes the idea. "These experiments are worth doing, whatever the challenges," he says. "It certainly sounds like there is an upside for people living near the airport. We'd need to know what it means for people further out. But the technique should be considered for Heathrow."

[Dave Gittins]

Whilst not wanting to deny the obvious advantages of more careful descent profile management without the classic noise of a "fist full" of spool up on finals, isn't the usefulness of this technique slightly outweighed by the considerably greater take-off noise which will not be diminished ???

Whilst appreciating that those who drive heavy metal for a living can make more carefully power limited take-offs under the right circumstances of field length and TOW, I for one will always want my right hand as near the front bulkhead as I can get it.

Personally I rate "power not being used" in much the same category as "runway behind" and "fuel in the bowser."

At the end of the day, noise reductions of a serious nature will only come from the powerplant manufacturers.

[Dave Gittins]

There are two very similar threads on this topic, one here and one on "Tech Log".

MERGE ??????

My reply on the latter was on the lines of ..... very good but no matter how well you glide quietly in to land, how do you get airborne again without making lots of noise ???

Personally, I consider limiting the power on take off to be right up there with "fuel in the bowser" and "runway behind one".

As in the past, it'll be Rolls, Pratt and GE who are responsble for the big noise reductions, not some dicky manoever that'll end in tears.

[Postman Plod]

Yep, living in Slough / Windsor, its not so much the landings that you hear, but the take offs. So what they going to do about that? Start the take-offs from 70km out? :rolleyes:

[Engine overtemp]

Dave Gittins

Personally, I consider limiting the power on take off to be right up there with "fuel in the bowser" and "runway behind one".

As you list your aircraft type as PA28 and are a PPL, I would not disagree that on light aircraft you are correct. However it is accepted practice (and indeed encouraged) on commercial jets to reduce power on take off. This has little to do with noise but is to do with preserving engine life and in turn reducing costs to the airline.:ok:

[spekesoftly]

I sincerely doubt the practicality of combining 'glide approaches' from a 70km final with accurate spacing and the strict adherence to speed control required during busy periods at major Airports.

[PAXboy]

Let a non-pilot muse for a moment ...

A/c arriving to London from North America. Winds are also from the west, so they travel another 70ks EAST, in order to come back another 70Ks????

If they turn onto base leg over Wembley or City of London as now, will they not keep fuel burn to a minimum?

Does HACAN want to increase fuel burn/pollution just to save a few decibels?? (I think I know the answer to that one ...) :rolleyes:

[Jerricho]

Somebody got something wrong!

CDA's in the London TMA start at 6000', with a restriction not to be below this outside 20 miles from touchdown (at night we also ensure aircraft do not iintercept the localiser inside 10 miles.) Also, it is my understanding that a flight is deemed not to have leveled out if the altitude isn't maintained for more than 2 nm.

[Daysleeper]

Another great idea that might work in the wide open spaces of the central US of A but would be a blinking nightmare in Europe ,
so for Brussels turn finals at Mastricht,
Heathrow somewhere out by southend,
Brum down by Oxford. and Frankfurt traffic would go neatly over the top of Hahn. Super.:sad:

[Vage Rot]

One could always shut down engines 2,3&4 and fly the approach on 1 - only 25% of the noise!!! Or invent some other B0llocks!

70 mile approaches indeed! We manage to achieve that on approach to some remote scottish airfields but that's straight in to the airfield. To line up on the runway at a great distance - loads of extra miles to fly, unless we build circular airfields!

The noise from air traffic is limited to an area of around 10 miles from the field and is only significant closer than that. Don't buy a house near an airfield then comlain!!!

Rant Ends!

[Young Paul]

The change of noise of aircraft above 4000' on the approach may be detectable to the human ear, but in the context of modern airliners, it is not significant. For example, at 4000', we are most of the way to City Airport - certainly further east than the West End. How many people would grumble about aircraft noise further east than the houses of Parliament?!

I would instead recommend tight circling approaches over the airfield, to limit the area which is affected by noise.

[747FOCAL]

I really find reporters to be extremely funny. :ok:

[Basil]

Can't see that it's much different from what we're attempting now except, as Paxboy says, we sure ain't going 35nm past destination before turning finals.

[BOAC]

Basil - perhaps you haven't been to CDG lately........:p

Why not move the airfield 70kms away? I think I'll write to the New Scientist.............

[747FOCAL]

If you really want to affect percieved noise levels and leave things as they are now make ILS accept a 5.5 degree glidescope and you will see serious noise improvements. :ooh:

[BEagle]

"..and Frankfurt traffic would go neatly over the top of Hahn"

A certain airline thinks that Hahn IS Frankfurt:E

[paulo]

Heh heh... 70km ahead? For 'that' airline, it could still be 30km after the 'destination'. :E

[wonko the sane]

Young Paul says : "How many people would grumble about aircraft noise further east than the houses of Parliament?!"

Wonko Says : Lots. This has been debated to death before, but I assure you there is a lot of Heathrow bound aircraft noise as far out as the Isle of Dogs.

[overstress]

Alternative research suggests the following:

Pilots should only accept approaches in CAVOK conditions. They should position the ac in VMC at will to a 'High Key' position of their choosing in the overhead, or its environs. This would be type specific.

They would then announce 'idle power', close the thrust levers, and manouevre, subject to wind, to a 'low key' position.

At this point, an 'Initial aiming point' 1/3 down the runway in use will be chosen.

The pilot will then select services, again in a type-specific manner, to achieve a power-off approach, reserving the final flap selection until landing with idle power is assured, thus bringing the touchdown aiming point to the fixed distance markers.

The advantages of this procedure are many, namely:

Increased pilot proficiency, especially, say, amongst ultra long-haul pilots at the end of a 12 hour sector

Reduced fuel usage (idle power throughout)

Lower noise (see above)

Greater entertainment for the passengers

Increased endorphin levels for the non-handling pilot


I will submit these ideas to the next edition of New Scientist

[DanAir1-11]

One small but rather notable omission thus far - TERRAIN

not always going to possible to line up and float on in with our bathroom slippers on from 70kms
certainly not in Euro-Alpen / Himalayan / (insert range of choice)
locations. Jet noise is unfortunately unavoidable, I think we all do what we can, where we can, as safely (hopefully)as we can, to limit it. NAP's are probably as good as they are going to get for those who suffer the noise and whilst often an inconvenience to crews at a critcal stage in flight, we all do our best. Jet noise has been drastically reduced over the past decade and I don't honestly see that we can get any quieter without a revolution in propulsion.

[Airbubba]

These low drag, idle approaches have been touted for the past couple of decades. The sim instructors can do them in their sleep and then brag about the fuel savings.

In the real world they are great when they work but inevitably someone will misjudge, have a tailwind, try to show off or otherwise deviate from the ideal profile and metal will get bent. Several carriers have gone back to the old concept of a stabilized visual approach with engines spooled by at least 1000 feet. Not everyone gets as much practice as Southwest and even they have been known to have a bad day with a tailwind and a late descent.

[BEagle]

I wish that some of these idiot tree-huggers had been in London in the 1970s with the racket of Tridents, 707s, Vickers FunBus and the like roaring in with gear down for several miles. You can barely hear the hum of an Airbus or the rumble of a 747 above the traffic noise these days....it really is a very insignificant factor compared to the noise back then.

The last time I heard ac noise in the City, it was the throb of 4 Merlins when the RAF Lancaster was doing a flypast. I don't think anyone complained.......

[100% N1]

Would it really be a good idea to do idle approaches? Sure, it will reduce noise, but what happens when you need to make a missed approach and the engines are at idle? Or you reach DH without becoming visual and have to descend even further while the engines spool up so you can begin to climb...

[fiftyfour]

100%N1 is right. The main point of the last few stages of extra flap on jet aircraft is to keep the engine in the high idle range which allows good speed control and quick acceleration if needed.

[Vage Rot]

PABTO departures and power against flap approaches for a few months at LHR Village strip. That'll make 'em realise how quiet ac normally are these days!


Or adopt the military method of dealing with noise complaints:

'It wasn't one of ours Madam, have you tried calling Gatwick?"

[Jerricho]

Hee-hee..........I like the way this guy thinks!!!

[davethelimey]

BEagle: you should take a stroll through SW1 and then tell us whether you think an Airbus, um, 'hums'. I guarantee you that it can drown out a conversation in a flat if the window's open!:)

[747FOCAL]

100% N1,

FYI - Even with the engines all off the 747 will ring about 100.3 EPNdB on the monitors from airframe noise during a flaps 30 landing.

There are no commercial jet aircraft where they would become completely buried in the 65 dB noise floor of any airport community shooting approaches with the engines off. :)

[PAXboy]

davethelimeyyou should take a stroll through SW1 and then tell us whether you think an Airbus, um, 'hums'. Indeed, from the ground I tend to find that the Bus has a distinct whine. It is probably engine manufacturer dependent. When inside them, there is a real 'cutting edge' noise at take-off and initial climb.

The answer probably lies with the Spotters. Ask them which Bus has which engines and which makes the most noise as they watch them go by.

[Tony_EM]

I never despatched any of the 744s with derated thrust since they all went out full or close to it (SQs ex LHR). But my question is; when using less thrust, wouldn't it mean a shallower climb and therefore a bigger noise 'footprint'?

Having lived in Richmond for a few years and worked all over the west of London recently, I'd have to say that aircraft noise on approach is no worse than traffic until you get closer to Hounslow, and as many have said, it's not just engines that make the noise. Quite often you can hear the ripping sound of the vortices long after the plane has gone.

I think for approach noise, the only advances left that will bring any significant reductions are; a steeper glide path which still gives the engines something to push against (4-4.5 deg?) and more height above the (richer) suburbs, cleaner flaps-deployed aerodynamics (which kinda defeats the object of them), and quieter engines (which seem to have gotten as quiet as they can get).

I reckon the whiners that live in areas affected by aircraft noise have only just moved there in the last decade or so, because the rest have seen massive reductions in noise levels due to the modern engines and phasing out of the old iron (BAC111s). Why they can't just learn to love the sound of a flying machine is beyond me, but they certainly knew the deal when buying their house.

As for departing aircraft, there seemed to have been a change to aircraft routes departing 09R at LHR after 9/11, as they seem to be doing a circuit of my garden in feltham now, where they used to fly much farther before turning right. Even then, some make VERY little sound, like the A330s and B777s. Very impressive. But like I said, I'd rather listen to the chest throbbing echos of Concorde (and watch her tip a wing to my garden) 10 times a day if I had my way.

BTW, any of you boys departing LHR 09R and doing a sharp right turn, mines the garden with the mown lawn, you can't miss it, it's the only one in Feltham.:8

[Dave Gittins]

Nah .. not the only one. My uncle's lawn's pretty good in Harlington Road West - that's the one they are using as an aiming point, straight off the wingtip in the right turn.

Have to say though being in his garden is quite a treat as the big boys go right off 09R. Looking across the whole wingspan of the big old noisy bird brings back such memories and now it's too late to take my camera next time I go visiting !!!!!!!!!