Performance /de-rated take-off

[badrace]

De-rated take off and flex take off ,some airlines do them both,for derated take off ,how do aircraft/engine manufacturer have these set reduced power settings meet certain regulations? since it might gets complicated when it comes to Vmcg issue.
I'm always curious about the performance optimization in which airbus seems to have more experience.Anyone can give me some lecture?

[johns7022]

Well I gather the derate numbers are certified for runway and climb gradient requirements...burning up valuable runway to that they can trend monitor an engine out to 25000 hrs before overhaul...

Passenger safety being number one of course....

Around here it looks like the 737s fly it to fence (8000 ft runway) then pull up..

The consensus being that after V1 has passed, your committed, lumbering down the runway waiting for V2, that if you lose an engine rotating at the fence(you planned accel/stop into the overrun) you now have the luxury of bringing up the good engine to max to get over those mountains ahead........lovely....

[Intruder]

De-rated take off and flex take off ,some airlines do them both,for derated take off ,how do aircraft/engine manufacturer have these set reduced power settings meet certain regulations? since it might gets complicated when it comes to Vmcg issue.

Vmcg is taken into consideration in derated/flex TO calculations.

With a fixed derate, you cannot use full thrust on the remaining engines if you lose one. With reduced thrust (assumed temperature), you can use full thrust. I don't know what Airbus uses for flex.

[badrace]

numbers

Max thrust should not be used during engine out take offs for de-rate for Vmcg consideration ; .however the airlines now must provide additional take-off performance charts as well as proper training for crew,since it's common sense to firewall the throttle when you feel chanlleged by the remaining runway.
My question again was: how do aircraft/engine manufacturers get these (i.e 6% 10% )prercentage of power certified ,are they just arbitary?do they need to test each power settings?Where do there numbers come from ,which regulation?

[john_tullamarine]

Basic rule is 25 percent max reduction flex for a given rating (although I understand AB has a 40 percent permission as they don't combine the two)

To get more, you need an artificially smaller engine by certifying a derate .. and then you can continue the reduction via flex.

Around here it looks like the 737s fly it to fence (8000 ft runway) then pull up..

That sounds like a significantly unbalanced takeoff with V1 having long gone and use of clearway. The later rotation approaching the end can give the impression of not much runway. Keep in mind that, for an unbalanced takeoff, only half the air distance to screen need be over the runway bits.

you now have the luxury of bringing up the good engine to max to get over those mountains ahead

That should never be necessary although it is optional. However, if you choose so to do .. do it slowly.

[FE Hoppy]

@JT
On out little E-Jets we've got an ATTCS system that will rapidly increase the thrust from a full 25% reduction to about 10% above Rated thrust. I've often wondered how that would look a kt or 2 above VMCG.

[Mad (Flt) Scientist]

Originally Posted by FE Hoppy

@JT
On out little E-Jets we've got an ATTCS system that will rapidly increase the thrust from a full 25% reduction to about 10% above Rated thrust. I've often wondered how that would look a kt or 2 above VMCG.

That would seem to violate part of FAR 25 Appendix I:

I25.4 Thrust Setting.

The initial takeoff thrust or power setting on each engine at the beginning of the takeoff roll may not be less than any of the following:

(a) Ninety (90) percent of the thrust or power set by the ATTCS (the maximum takeoff thrust or power approved for the airplane under existing ambient conditions);

That seems to be saying, at least as I read it, that the ATTCS delta should be 10% above the thrust set for that takeoff, not 10% above the Rated thrust. Whereas what you describe is more like 50% (75% rated to 110% rated).

Our equivalent system works, IIRC, on a delta to the set thrust, not a delta to the Rated thrust.

[Wizofoz]

Basic rule is 25 percent max reduction flex for a given rating (although I understand AB has a 40 percent permission as they don't combine the two)

GE-90s are also rated for 40%, John- we will regularly take off with a 76deg Assumed Temp in the GE powered 777s.

[Wizofoz]

The consensus being that after V1 has passed, your committed,

Not so much the "Consensus" as the bleeding obvious- thats what V1 IS.

lumbering down the runway waiting for V2

No, Vr. V2 come later.

[robert f jones]

johns7022

I think you need to brush up on your performance study/lessons. Less power used when not needed significently reduces the risk (however small) of engine failure and the problem of reaching Vr / V2 at the end of the take off run and Take off distance available.

[johns7022]

I guess the consensus is that when you make a derate takeoff, there is less of a chance of engine failure then at max takeoff...

Interesting theory...given the whole point of derate take offs is to trend monitor the engines out as far as you can to save money on overhaul cost..

So let's do the math...you run a corporate jet to 3500 hours, and do max take offs every flight if you want..

Or you do some max take offs, some derates and you get to enjoy doing them all the way out to 25000 hrs...

Hmm....let's see...I am at the end of the runway with a couple of 25000 hrs engines that the company mechanic said was OK...and I now need to get over those hills...or I am in a plane that has 3000 hour engines....

How come I feel safer with the 3000 hour engines...is it just me or am I missing something?

[Wizofoz]

...is it just me or am I missing something?

...Decades of data involving millions of takeoffs showing the incredible reliability of large jet engines and a virtual zero incidence of accidents due to engine failure after takeoff?

Yes derate saves money, because it saves the engines.

I am in a plane that has 3000 hour engines

I take it you fly Biz jets...Do you REALLY want to start making comparisons between the saftey records of airliners and biz jets?

[n1_spindown]

much easier on the engines = saves money

[johns7022]

I wouldn't have any problem comparing safety records between biz jet ops and airlines..

If the consensus is that trend monitoring an engine out as far as you can safely do so is ok...then I think it should be ok for biz jet operators to do it as well...fair is fair.

[Wizofoz]

Sure.

Do you have the infrastructure, maintenece systems and large body of data to prove it provides equivelent saftey?

If so, by all means put in the requests for variations of the regs. It should only cost several million dollars.

That's what airlines and airline manufacturers have had to do.

I wouldn't have any problem comparing safety records between biz jet ops and airlines..

EBACE: Business aviation not as safe as it is cracked up to be?

This team found that the fatal accident rate for all business jet civil operations is more than eight times that for large Western jets in airline operation, and four times that for large Western-built turboprops flying commercial operations.

[johns7022]

You mean the special interests lobby's, the FAA in your back pocket...to bend and twist the regs to allow planning accel stop into overruns, put 200 hr ab initios into the right seat and have your own mechanics determine with a look see if an engine at 20,000 hours is good enough to go to 25000 hrs..

Nope you got me..corporate aviation doesn't have the where with all to pull that off...

[Denti]

That sounds very familiar, wasn't the same guy around last year spouting the same nonsense?

[Wizofoz]

You mean the special interests lobby's, the FAA in your back pocket

So perdictable that someone of that mindset is also an American Chavenist.

No, those procedures are used world-wide, ratified by a huge number of regulaory agencies, many of whom require their own, entirerly idependent saftey case.

So, Airline do all that, and are STILL EIGHT TIMES safer than Biz Jets?

Do you have trouble getting life insurance?

[johns7022]

'I think what we have here is a failure to communicate'

Let's take a hypothetical....same plane, same 5000ft runway, 1000ft over run, mountains up ahead, have to fly a complicated SID....and your choice is this..

- You can put a 200 hr ab initio pilot right seat or experienced captain.

- You can have 3000 hr engines or 25000 hr engines

- You can run max take off, get off early, or run your accel stop numbers into the over run, and rotate at the fence...

And the justification IS? 'Well gosh, you know...we are trying to save money on engine overhaul costs....yeah yeah I know...we just bought a fleet of all new A300s...yeah yeah, the CEO is making 40 million a year...yeah yeah, I know we chuck money down the toilet all over...but you know, we are really TRYING...and that's what counts.'

lol....always good for a chuckle when I come here....

[Wizofoz]

Certainly is a chuckle when clowns like you appear.

What exactly is your evidence that Airline practices are in any way unsafe?

Are you aware that the accident rate for two Captains flying together is higher than for experienced Captain/ Inexperienced FO?

Where do YOUR FOs gain experience?

If what we do is so heinous, why do you biz jet guys crash so often?

Are you aware you are MORE LIKELY to have an engine failure if you use max thrust instead of flex where available?

Are you aware that it HAS been shown that it is safer to leave a perfectly functional engine alone rather than tear it down every few thousand hours for no good reason?

In other words, each of these has been shown to enhance safety AND cost.

Seems like you like to spend your employers money JUST to make things LESS safe because your ego is to big to actually learn the facts about your own profession.