Noise Abatement

[DOC.400]

Living under westerley departures from Heathrow(Dover and associated departures I think) it's sometimes quite alarming to hear noise abatment being practiced 3000' or so above my roof!

How is noise abatement carried out/decided in practice? On reaching a certain height? speed? automaticaly or manually?

Thanks in anticipation.

DOC

[sanjosebaz]

Can it be? A complaint about noise abatement? Can be a little disconcerting when inside the plane too, particularly as it was in Concorde last Monday, in low cloud and accompanied by smoke alarms going off (oil in the ducting, allegedly, so no problem)! The deceleration for noise is particularly dramatic in the rapid pointy thing and is done just over one minute from brakes-off.

It's a manual change to a pre-determined thrust setting, I believe.

[G.Khan]

Out of LHR in a heavy B747-400 we would not derate the take off at all, use full power, select auto pilot at 400', (Company SOP to better comply with min noise routing and not over fly the monitors), at 1000'agl the FMS had been pre programmed to reduce to normal climb thrust, climb to 4000'agl and then carry on with acceleration and clean-up.

[747FOCAL]

lol

[steve1969]

In a 747-400, by how much (if at all) would you pitch the nose down to facilitate acceleration prior to cleaning up the configuration?

[G.Khan]

Good question, not very much but it would be done by the auto-pilot anyway, the initial climb pitch angle will reduce considerably when power is reduced at 1000'agl, I would have to check it out and come back for actual numbers, (which would be small), but don't have access anymore!

747FOCAL, sorry not up to date with chat abbreviations, what does 'lol' stand for? <img src="frown.gif" border="0">

[The_Banking_Scot]

( Lol)Laughing out Loud ? <img src="smile.gif" border="0">

[411A]

747FOCAL just does not appreciate pilots' attempts to reduce noise, I guess. But not being a pilot, would have no idea of the skill required to achieve a really quiet departure.
Most airlines try to be as quiet as possible, not an easy task at times.
Perhaps 747FOCAL would like to recommend a better procedure for the -400 (or any other aeroplane)instead of LOL <img src="rolleyes.gif" border="0">

[747FOCAL]

411A- I told you I would stop in the other forum. You can't look at the name and figure it out can you?

[411A]

747FOCAL....appreciate your input, but the question still stands.....how, IN YOUR OPINION, can flight crew reduce noise by changing operational procedures. You don't have to give away trade secrets here, just a "hint" (or two) will do.
Surely you must agree that this would be better than.....LOL.
Over....

[Busta Level]

On the A330 we'll climb at max rate (=slow speed) to 1000' AAL, then pitch down (change in pitch from 15-20 degrees nose up to about 10 or less depending on weight) whilst reducing thrust. Mostly flown manually on the 330 (depending on the departure) because the simultaneous reduction of thrust and pitch can be alarming when the A/P is controlling the pitch. We try to be a bit more gentle!

This is then followed by the acceleration phase, where we are climbing more slowly and accelerating to 250 knots, bringing the flaps in as we go.

The idea behind it is to get to an altitude as quickly as possible where the noise footprint is minimised, rather than scream across the countryside accelerating at low levels!

We also try to reduce noise on the approach as much as possible (although the 'landing' footprint is always much bigger then the takeoff one) by trying to maintain a continuous descent and configuring the aircraft later rather than earlier - ie avoid dragging it in level with everything hanging out for 10 miles!

[747FOCAL]

411A- Depends on the airplane. If it makes sense, we are up against a wall when it comes to new technology(hardware) aimed at reducing noise levels. Operational procedures is one way that we can realize viable noise reductions that actually have impact on monitored levels. The common suggested procedures are a good start but there is more that we can be doing. Busta Level talks about his cutback procedure that he flys manually so as to ease the sensations on the passengers. Well his way of doing is going to add more noise than what the airplane is programmed to do on it's own. Anymore than that and I am going to be giving up some things that I hope will help the airport community and make me some money. :) :) <img src="wink.gif" border="0">

[Busta Level]

More Noisy? How? The thrust is still brought back to the same level (CLB) regardless of the pitch angle being flown manually, and it happens at the same height (1000' AAL). The pitch angle only influences the acceleration rate during this phase, not the thrust setting! <img src="confused.gif" border="0">

If anything, the A/P way of doing it means more noise, as the pitch down is more sudden, therefore the acceleration phase starts closer to the ground = more percieved noise.

[G.Khan]

The auto pilot on the B747-400 is a very, very gentle beast and the pich change at throttle retard, (1000agl) is very smooth.

[eyeinthesky]

With regard to the initial reference to 3000 ft, from an ATC point of view, we are not allowed to turn a/c off the NPR until they have passed 4000'. That is why you will often hear the instruction: "Upon passing 4000 ft, fly heading 150" or whatever. Of course by then they are well past the monitors, but it reduces the complaints from the residents of Chertsey when the Dover departures scream off toward EPM at 2000ft!

[747FOCAL]

Busta - It has to do with time integration at cutback. When a cutback procedure is not done correctly it can cast the noise footprint hundreds of feet further. Doesn't seem like much unless your house happens to be in that extra 500 ft. If you take the extra 500 ft(or whatever) and multiply it by the length of the noise footprint a rough calculation of how many square blocks just got more noise than they otherwise would have. Most airports want to keep the noise footprint above 85 dBa on the airport property. Doesn't happen very often in a 747-400.