Hi All,

 

I'm getting to grips with the engine derates, acceleration heights and reduced thrust combinations that can be entered into the CDU for noise abatement and such.

 

But can't quite work out when the reduced thrust at a particular flap setting would be used over an altitude.

 

Does anyone know or have experience of this ?

 

Regards

Simon Grant

I don't really understand the question...

 

Thrust reduction from TO to CLB usually comes at 1500ft AAL.

I don't really understand the question...

 

Thrust reduction from TO to CLB usually comes at 1500ft AAL.

 

When setting up the CDU/FMC you have the option to have reduced thrust kick in at an altitude AGL or when the aircraft is configured for a particular flap setting.

 

Last night I had the thrust reduction occur when the aircraft was at a flaps 1 which then reduced the thrust to below the flaps 1 speed. Obviously not the option I should have chosen for that particular take off.

 

So it just got me wondering what circumstances would be needed to use this.

 

Regards

Simon

 

 

When setting up the CDU/FMC you have the option to have reduced thrust kick in at an altitude AGL or when the aircraft is configured for a particular flap setting.

 

Right. I don't use that, so it did not click. I prefer my ICAO NADP profiles.

 

 

 

Last night I had the thrust reduction occur when the aircraft was at a flaps 1 which then reduced the thrust to below the flaps 1 speed.

 

Now - here is your problem. In climb, thrust does not control the speed. Thrust controls the rate. Speed is controlled by pitch - when the trust is reduced, you should pitch down to maintain the speed.

 

 

When setting up the CDU/FMC you have the option to have reduced thrust kick in at an altitude AGL or when the aircraft is configured for a particular flap setting.

 

That's the T/O to CLB kickover setting.  Essentially, there are a few things at play here:

1. Engine wear - running your engines at T/O longer than necessary shortens engine life.  The cost of the GE90 being somewhere around $24M, you can see why you'd want to make them last as long as possible.
2. Noise abatement - for some reason, people like to put houses next to airports, and in order to allow an airport to continue operating, airports often enforce some restriction for thrust modes, based on altitude and/or distance.

 

 

Last night I had the thrust reduction occur when the aircraft was at a flaps 1 which then reduced the thrust to below the flaps 1 speed. Obviously not the option I should have chosen for that particular take off.

 

Eh...sounds more like you weren't flying the plane properly and don't quite understand the concepts of a proper takeoff (sorry - but unless someone taught you before, nobody can fault you for that).

 

Speed - though a result of thrust - is dependent on a combination of factors.  A 777 at a low pitch angle is going to be going a lot faster than a 777 pointed up at 30 degrees.  So, if you're going to use the flaps-based trigger, you should ensure that you're above the Flap 5 indication (and accelerating) on the speed tape before selecting Flap 1.

 

The proper takeoff profile is described in the FCTM (page 3.2 and following text).

Thanks for the replies guys.

 

I confess it wasnt a properly thought out take off it was more of a "i've just read this in the manual let see what it does" kind of thing.

 

But it did make me wonder when a pilot would choose this method over setting an altitude.

 

More studying for me and thanks

 

Simon

The clb reduce at Flap one seems to be a 777 specific option. Most airports in europe have noise reduction rules. In EDDT you climb to 800ft agl reduce thrust to not less than clb and climb to 1500ft agl. Then begin acceleration to clean speed or 250kts.

Yes, it is an option you can set as default, which some airlines have.

 

I'm new to that particular option myself, 2 questions I have:

 

-I always thought (and recall seeing in a few instances) that simply selecting flaps 1 engages the thrust reduction, apparently in the PMDG model the flaps have to retract all the way to 1 before thrust is reduced. Is this an option as well?

-With flap 1 thrust reduction, do you retract to flaps 1 when passing the appropriate flap retraction speed or is there a minimum altitude also before doing this typically (eg 400, 800, 1000 AGL)?

 

 

-I always thought (and recall seeing in a few instances) that simply selecting flaps 1 engages the thrust reduction, apparently in the PMDG model the flaps have to retract all the way to 1 before thrust is reduced. Is this an option as well?

 

With the large difference between V2+[additive] and your Flap 1 maneuvering speed, would you really want your thrust to be reduced prior to the flaps actually reaching Flap 1?

 

 

 

-With flap 1 thrust reduction, do you retract to flaps 1 when passing the appropriate flap retraction speed or is there a minimum altitude also before doing this typically (eg 400, 800, 1000 AGL)?

 

Company SOP would likely be the factor here, unless there was a prescribed procedure otherwise.

With the large difference between V2+[additive] and your Flap 1 maneuvering speed, would you really want your thrust to be reduced prior to the flaps actually reaching Flap 1?

Depending on acceleration, sure.

Depending on acceleration, sure.

 

...which you'd be killing by reducing to CLB thrust on Flap 1 selection if it was a reduction at selection, not actual flap position.

...which you'd be killing by reducing to CLB thrust on Flap 1 selection if it was a reduction at selection, not actual flap position.

Situation-dependent, some cases yes, some no.

Situation-dependent, some cases yes, some no.

Try running that explanation by the FAA and see how they take to it.

 

"So the aircraft commands less thrust prior to the flaps reaching their commanded position. Does this not have an associated safety implication?"

It's situation-dependent - some cases, yes; others, no."

"Right. Well thank you for your time..."

Mh maybe I have a pretty big error in reasoning but you'll select a lower Flap setting after reaching a save speed for this lower setting isn't it? So take 2 situations as an example:

 

1st: departing EDDT (which dictates CLB thrust @800 and acceleration @1500). It's commanding CLB at 800 AGL and acceleration at 1500 AGL. With this option you'll manually set CLB Thrust at 800 and climb further. At 1500AGL you lower the nose and accelerate.

 

2nd: departing let's say EDDM (which dictates CLB & acceleration @1500): you'll lower you'r thrust to clb and lower your nose. You'll accelerate and retract flaps.

 

Now think of F1 thrust reduction by selection. Case EDDM you'll lower nose to accelerate to flap retraction speed. You have TO power set. At flap reduction speed you'll retract and thrust get's reduced too. You have lower drag, same pitch and some lower thrust. But isn't it the same than 2nd example? But instead of setting CLB thrust at 1500AGL you'll wait until flap retraction. But speed and thrust at selecting flaps will be the same +- some seconds to spin to that rating.

 

Maybe I am really wrong in that. Just asked a 738 captain this evening and showing him this example before he left. This are his words.

 

 

Edit: Another thought: You'll select F1 at the correct speed and then thrust is reduced. Or do you select lower flap to reduce thrust even at V2+15-25? The last case seems to be very dangerous to me; think of some gusty conditions or wind sheer.

Try running that explanation by the FAA and see how they take to it.

 

"So the aircraft commands less thrust prior to the flaps reaching their commanded position. Does this not have an associated safety implication?"

It's situation-dependent - some cases, yes; others, no."

"Right. Well thank you for your time..."

No, I'm not talking FAA or safery or aircraft certification or otherwise. You are taking my words of context, so why would I say that to the FAA? I'm simply referencing acceleration. If you have an abundance of thrust, and are light enough, then reduce that thrust but yet still have an abundance (and attitude, etc etc all allow), you will still accelerate. Hence, in some cases, like my original statement, yes. I'm not going to argue that point or safety hypotheticals and it's a tangent anyway, so that's my last word on that subject.

 

Not claiming to be an expert by any means, I'm the first to admit that. Not trying to pick a fight either. Flew a 777 sim once for a few hours that didn't use flap reduction method, and not it is scientific or hard fact but a few of the World Air Routes 777 DVDs show this, hence my question to the general community of experts. A few aircraft I've flight tested as well have reduction behavior like this.

 

Thank you.