View Full Version : Auto Throttle vs Noise

10th Nov 2004, 15:04
Reading HTBJ and found something which I cannot work out. A number of methods are mentioned on how to reduce noise on final appch. One is not to use Auto Throttle.

How does having the auto throttle engaged increase engine noise and is their policies at some aerodromes/companies relating to their use.

10th Nov 2004, 15:23
When using auto throttle the amount of thrust varies up and down which I assume you know. Sometimes the thrust is lower than a steady state approach setting and sometimes the thrust is higher. You end up with noise spikes when the thrust is higher. More thrust = More noise.

A person looking at monitor data vs. the certified EPNL of the aircraft may wonder why the aircraft monitors way above it's certified levels. Auto throttle is usually responsible for this. :)

11th Nov 2004, 09:55
747FOCAL; one aircraft widely known to measure higher than its certified EPNLs on approach is the RR powered 747-400. The GE and PW variants appear fine by all accounts. By that reckoning, are you implying that RR aircraft routinely use auto throttle but GE and PW powered -400s do not.

Care to elaborate?

My understanding is that auto throttle simply causes frequent variations in power setting, thus causing transient noise, which is sometimes cited as more annoying than a steady state level.

11th Nov 2004, 19:16
If I told you what I know about the RR powered 747-400 and 767 and the "noise" you talk about I would have to kill you. :p

Auto throttle does cause all aircraft that use it to sometimes be louder and sometimes be quieter than certified. Well accept for the above mentioned aircraft. :E

11th Nov 2004, 19:58
Original message Deleted answered through PM.


11th Nov 2004, 20:39
Mutt, I totally agree... 747FOCAL should tell us what he (or she) knows about the RR 747/767!! :p

Mutt, for info, the 'widely known' noise readings I was referring to are published in the following report (see Figure 8 for the RR powered 747/767 noise results)


(dial-up users beware though - it's nearly 9MB!)

17th Nov 2004, 14:08
sorry to bump this but still waiting for a response (of some sorts) from 747FOCAL. Are you gonna reply?

17th Nov 2004, 14:27
I already told in private to people I am familiar with at PPRUNE. :)

17th Nov 2004, 20:54
:hmm: OK fair enough, but can I politely suggest then that you stop posting messages along the lines of "If you only knew what I new..." on a PUBLIC forum such as this one. Doing so is pointless if you have absolutely no intention of backing up your 'talk' with actual facts (if they exist) and it just makes you sound self-important.

17th Nov 2004, 21:35
I am important in my own world...............:E

I did tell those I am familiar with. I do not know you and in defense of the industry I chose to make the information private.

18th Nov 2004, 04:21

747FOCAL replied to me via PM. His reasoning makes sense and in this corporate world of ours, i can understand why he doesnt want it made public......

Sorry, but i cant share his information. :(