aerotech777
Topic Author
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Reduced Versus Full Takeoff Thrust

Wed Oct 26, 2011 5:37 pm

Hi,

How often (approximate percentage if possible) do you use assumed or derated takeoff thrust versus full takeoff thrust?

Feedback appreciated.
 
wilco737
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RE: Reduced Versus Full Takeoff Thrust

Wed Oct 26, 2011 6:25 pm

Quoting aerotech777 (Thread starter):
How often (approximate percentage if possible) do you use assumed or derated takeoff thrust versus full takeoff thrust?

I am FO on 744 and I did almost 100 flights this year and only ONCE we had to use full take off thrust. Rest was all derated.
Same on the MD11 I flew before. Most of the times reduced, only once in a while full thrust.

wilco737
  
 
XFSUgimpLB41X
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RE: Reduced Versus Full Takeoff Thrust

Wed Oct 26, 2011 7:08 pm

I would say a good 90-95% of our takeoffs are reduced/FLEX thrust.
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BoeingGuy
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RE: Reduced Versus Full Takeoff Thrust

Wed Oct 26, 2011 7:19 pm

Quoting XFSUgimpLB41X (Reply 2):
I would say a good 90-95% of our takeoffs are reduced/FLEX thrust.

FYI, just as an aside, Boeing calls it "Assumed Temperature Derate" what Airbus and McDonnell Douglas call/called "Flex Power". Some Boeing airplanes also have a Fixed Derate, which is usually 10% and 20%.

My understanding is also that some sort of takeoff derate is used about 99% of the time, except at certain high altitude or short runway airports like SNA.
 
kcrwflyer
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RE: Reduced Versus Full Takeoff Thrust

Wed Oct 26, 2011 7:27 pm

Quoting BoeingGuy (Reply 3):
My understanding is also that some sort of takeoff derate is used about 99% of the time, except at certain high altitude or short runway airports like SNA.

I've heard that most aircraft even get out of SNA with a certain derate, and that PHX requires more thrust.
 
FlyMKG
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RE: Reduced Versus Full Takeoff Thrust

Wed Oct 26, 2011 9:19 pm

We use reduced thrust around 80% of the time on our 727 freighters.

FlyMKG
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Mir
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RE: Reduced Versus Full Takeoff Thrust

Wed Oct 26, 2011 11:01 pm

We never do reduced thrust. Push the thrust levers to the takeoff detent, FADEC takes care of the rest.

-Mir
7 billion, one nation, imagination...it's a beautiful day
 
boeingfixer
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RE: Reduced Versus Full Takeoff Thrust

Thu Oct 27, 2011 12:07 am

Quoting Mir (Reply 6):
We never do reduced thrust. Push the thrust levers to the takeoff detent, FADEC takes care of the rest.

What aircraft might that be?

Cheers,

John
Cheers, John YYC
 
Mir
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RE: Reduced Versus Full Takeoff Thrust

Thu Oct 27, 2011 2:54 am

Quoting boeingfixer (Reply 7):
What aircraft might that be?

CJ3. The FADEC sets the power so that the takeoff detent corresponds to max rated power (even if the engine is capable of doing more). If it's hot or high, then you might not be able to get max power, but you'll get whatever the engine is capable of (and the published numbers reflect this).

-Mir
7 billion, one nation, imagination...it's a beautiful day
 
SUPRAZACHAIR
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RE: Reduced Versus Full Takeoff Thrust

Thu Oct 27, 2011 3:41 am

Assuming the aircraft has no MEL restrictions, every takeoff except first flight of the day and 10kt+ tailwind takeoffs. This is on the Dash-8-Q200/300.
 
CosmicCruiser
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RE: Reduced Versus Full Takeoff Thrust

Thu Oct 27, 2011 4:21 am

We always use "flex" if it's available.
 
pilotpip
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RE: Reduced Versus Full Takeoff Thrust

Thu Oct 27, 2011 4:44 am

The only time we are required to do a max thrust takeoff is on a contaminated runway with braking action less than good. The only time we really see this is with snow/slush. I like to do them any time there is a windshear advisory or when I'm at HPN. Other than that we do what the ACARS tells us performance wise.

This is in the ERJ-170. I haven't done a max takeoff in weeks and probably do less than 20 a year.
DMI
 
BoeingGuy
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RE: Reduced Versus Full Takeoff Thrust

Thu Oct 27, 2011 6:02 am

Quoting suprazachair (Reply 9):
every takeoff except first flight of the day

What is the significant of the first flight of the day in regards to derated takeoffs?
 
Max Q
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RE: Reduced Versus Full Takeoff Thrust

Thu Oct 27, 2011 7:19 am

Quoting Mir (Reply 8):

CJ3. The FADEC sets the power so that the takeoff detent corresponds to max rated power (even if the engine is capable of doing more). If it's hot or high, then you might not be able to get max power, but you'll get whatever the engine is capable of (and the published numbers reflect this).

Seems quite unusual to push the engines that hard every take off and must increase maintenance costs significantly.



Never heard of any jet operator not taking advantage of the ability to routinely do reduced power take off's.
The best contribution to safety is a competent Pilot.
 
saab2000
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RE: Reduced Versus Full Takeoff Thrust

Thu Oct 27, 2011 9:18 am

I would guess that we flex at my carrier 95%-98% of the time. I have used full thrust myself only a few times that I can remember in the past few months and both times were full airplanes and short runways. The engines will be up to 100º hotter on a full thrust take-off than on a flex thrust t/o, though 75º is probably more normal.
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JETPILOT
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RE: Reduced Versus Full Takeoff Thrust

Thu Oct 27, 2011 9:50 am

We use full thrust whenever,,,,,

Snow/slush/standing water is present on the runway
Anytime there is a tailwind
Crosswind over 12 knots
Anytime wing/engine anti ice is in use
When climb power is higher than reduced power
When there is an unbalanced field length
Anti-skid is INOP
Windshear is reported or suspected
Any EPR gauge INOP
 
Mir
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RE: Reduced Versus Full Takeoff Thrust

Thu Oct 27, 2011 10:33 pm

Quoting Max Q (Reply 13):
Seems quite unusual to push the engines that hard every take off and must increase maintenance costs significantly.

I don't disagree, but I just fly it the way I'm trained to fly it.

-Mir
7 billion, one nation, imagination...it's a beautiful day
 
tb727
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RE: Reduced Versus Full Takeoff Thrust

Thu Oct 27, 2011 11:14 pm

Quoting jetpilot (Reply 15):

We use full thrust whenever,,,,,

Snow/slush/standing water is present on the runway
Anytime there is a tailwind
Crosswind over 12 knots
Anytime wing/engine anti ice is in use
When climb power is higher than reduced power
When there is an unbalanced field length
Anti-skid is INOP
Windshear is reported or suspected
Any EPR gauge INOP

We also have to do a max blast in the past 7 days when we look at the logbook. I'd say 75-80% are reduced at my company.
Too lazy to work, too scared to steal!
 
aerotech777
Topic Author
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RE: Reduced Versus Full Takeoff Thrust

Sat Oct 29, 2011 5:21 pm

Thank you for your feedback.

Do you use wing anti-ice during full takeoff thrust?

A reduced takeoff thrust may increase the airplane-to-ground noise level as result of a lower flight path. If certain airports have some noise restrictions, do you use reduced takeoff thrust or full takeoff thrust?

Feedback appreciated.
 
tb727
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RE: Reduced Versus Full Takeoff Thrust

Sat Oct 29, 2011 8:51 pm

Quoting aerotech777 (Reply 18):
Do you use wing anti-ice during full takeoff thrust?

No, in the planes I have flown we always waited until we were in the air, typically after gear retraction and/or when we started bringing up the flaps. Engine anti-ice yes.
Too lazy to work, too scared to steal!
 
Mir
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RE: Reduced Versus Full Takeoff Thrust

Sun Oct 30, 2011 3:00 am

Quoting aerotech777 (Reply 18):
Do you use wing anti-ice during full takeoff thrust?

Not necessarily. It's entirely possible to do a full thrust takeoff when the weather is nice.

But if the wing anti-ice is on, we will definitely be using full thrust (well, we use it anyway like I said, but even if it were an option, I wouldn't even think about it in that scenario).

-Mir
7 billion, one nation, imagination...it's a beautiful day
 
SUPRAZACHAIR
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RE: Reduced Versus Full Takeoff Thrust

Thu Nov 03, 2011 12:24 am

Quoting BoeingGuy (Reply 12):
Quoting suprazachair (Reply 9):
every takeoff except first flight of the day

What is the significant of the first flight of the day in regards to derated takeoffs?

First flight of the day is going to have the highest chance for an engine failure, so you'll want normal takeoff power if that were to happen.
 
XFSUgimpLB41X
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RE: Reduced Versus Full Takeoff Thrust

Thu Nov 03, 2011 12:28 am

Quoting suprazachair (Reply 21):
First flight of the day is going to have the highest chance for an engine failure, so you'll want normal takeoff power if that were to happen.

You're increasing the chances of an engine failure by running it even harder first flight of the day...
Chicks dig winglets.
 
XFSUgimpLB41X
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RE: Reduced Versus Full Takeoff Thrust

Thu Nov 03, 2011 12:31 am

Quoting BoeingGuy (Reply 3):
FYI, just as an aside, Boeing calls it "Assumed Temperature Derate" what Airbus and McDonnell Douglas call/called "Flex Power". Some Boeing airplanes also have a Fixed Derate, which is usually 10% and 20%.

I was just trying to give a "cover all" term, as I've flown Bombardier, McDonnell Douglas, Boeing, and Airbus airliners.  

The 737NG had the fixed derate as well as assumed temp on top of that... all the other's I've flown had a temperature only derate.
Chicks dig winglets.
 
DashTrash
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RE: Reduced Versus Full Takeoff Thrust

Thu Nov 03, 2011 12:16 pm

Quoting Max Q (Reply 13):
Seems quite unusual to push the engines that hard every take off and must increase maintenance costs significantly.

It might be a Citation thing. In the X we push it to the takeoff detent each time, which is the highest possible setting in the aircraft. The FADEC takes care of the rest. With us, you're usually in the 83-86% N1 range. I've heard it's due to rudder authority if you lose an engine.

I know the G200 guys do the same thing, but are spooling up close to 100%.
 
foxxray
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RE: Reduced Versus Full Takeoff Thrust

Thu Nov 03, 2011 12:29 pm

Quoting DashTrash (Reply 24):
It might be a Citation thing. In the X we push it to the takeoff detent each time, which is the highest possible setting in the aircraft. The FADEC takes care of the rest. With us, you're usually in the 83-86% N1 range. I've heard it's due to rudder authority if you lose an engine.

I know the G200 guys do the same thing, but are spooling up close to 100%.

Same thing on the Citation Mustang and Beech Premier...
 
Rara
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RE: Reduced Versus Full Takeoff Thrust

Thu Nov 03, 2011 3:28 pm

One thing I've always wondered: the "assumed temperature derate", or flex thrust, basically means that the aircraft is given a "fake" outside temperature to artificially reduce takeoff thrust, right? Why then is takeoff thrust lower, the higher the assumed temperature is? Wouldn't the aircraft normally need higher power with higher temperatures?
Samson was a biblical tough guy, but his dad Samsonite was even more of a hard case.
 
BoeingGuy
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RE: Reduced Versus Full Takeoff Thrust

Thu Nov 03, 2011 10:46 pm

Quoting XFSUgimpLB41X (Reply 23):
The 737NG had the fixed derate as well as assumed temp on top of that... all the other's I've flown had a temperature only derate.

Yeah, Fixed Takeoff derate is baseline on the 737, 747, 777 and 787. It's a priced option on the 757 and 767 so most of those models don't have it. All models have the Assumed Temperature Derate.

In other words, most 757 and 767s only have Assume Temperature derate; other models have either or you can a combination of both as you state. There is an upper limit of total derate that the system will allow you to do - 25% IIRC. In other words, you can't put in an Assumed Temperature of 99C and a 20% derate and get some really really low takeoff thrust.

There's another oddball 777 custom option that a few customers insisted on (apparently to mimic something the A340 does?) that allows a much higher Assumed Temperature Derate but inhibits Fixed Derates, but we won't dwell on that.

We are talking takeoff derates here. Climb Derates on all Boeing models are just the two Fixed Derates.



Quoting Rara (Reply 26):
One thing I've always wondered: the "assumed temperature derate", or flex thrust, basically means that the aircraft is given a "fake" outside temperature to artificially reduce takeoff thrust, right? Why then is takeoff thrust lower, the higher the assumed temperature is? Wouldn't the aircraft normally need higher power with higher temperatures?

You ask a good question. It's confusing. It's the opposite of the way you are thinking about it. The hotter it gets, takeoff performance is reduced. Engines and aerodynamics are less efficient at higher temperatures. So at +40C engine and takeoff performance will be less than if it were +5C.

Supposing it is +5C outside. By entering an assumed temperature of +40C, you are telling the airplane to pretend like it were really +40C and give me that same level of reduced takeoff performance. So, it would derate the thrust such to mimic the reduced performance that the airplane would have had if it were +40C outside.

So that's why an Assumed Temperature Derate reduces thrust.

[Edited 2011-11-03 15:55:31]
 
Fabo
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RE: Reduced Versus Full Takeoff Thrust

Fri Nov 04, 2011 12:53 am

Quoting BoeingGuy (Reply 27):
There's another oddball 777 custom option that a few customers insisted on (apparently to mimic something the A340 does?) that allows a much higher Assumed Temperature Derate but inhibits Fixed Derates, but we won't dwell on that.

What is that good for?   Seems quite the contrary of what could be actually be beneficial for 777 - more fixed derates - as I understand that in case of 777 with very light load, Vmca at TO (as computed for D-TO as I understand) could lead to values too high? Whereas with TO-1/2/x Vmca is actually computed for derated thrust? Do I understand this right?

As a sidenote, if I were to get a 777, throw everything out, including seats, upholstery, non-essential wiring, basicaly anything not fundamentaly required, minimum fuel and most powerful engine variant available, could I theoreticaly get into a situation that even a 25% derate would not let me depart as it would lead to a V2 < Vmca?

Quoting BoeingGuy (Reply 27):
So that's why an Assumed Temperature Derate reduces thrust.

Would the actual limiting factor in real temperature be EGT?
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Mir
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RE: Reduced Versus Full Takeoff Thrust

Fri Nov 04, 2011 4:11 am

Quoting DashTrash (Reply 24):
I know the G200 guys do the same thing, but are spooling up close to 100%.

For what it's worth, the Challenger 300 works the same way - thrust levers to the TO detent (except that that's not as high as they go - there's a detent above that for extra thrust in an emergency) on each takeoff, and let the FADEC take care of things.

-Mir
7 billion, one nation, imagination...it's a beautiful day
 
tdscanuck
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RE: Reduced Versus Full Takeoff Thrust

Fri Nov 04, 2011 6:36 am

Quoting Rara (Reply 26):
One thing I've always wondered: the "assumed temperature derate", or flex thrust, basically means that the aircraft is given a "fake" outside temperature to artificially reduce takeoff thrust, right?

Yes.

Quoting Rara (Reply 26):
Why then is takeoff thrust lower, the higher the assumed temperature is?

As outside temperature goes up, all temperatures in the engine go up (all the temperature ratios say the same but the inlet temperature is increasing). At some outside temperature, you'll hit the point where some component inside the engine hits its temperature limit...if you go any higher than that, you have to reduce engine thrust to avoid destroying whatever your critical component is (often the HPT). So, as temperature goes up, the engine has to pull back to keep temperature within allowable operating bands.

Quoting Rara (Reply 26):
Wouldn't the aircraft normally need higher power with higher temperatures?

No. The aircraft needs exactly the same thrust regardless of outside temperature. The issue is how hot the engine has to get to provide that required thrust. At very high temperatures the engine cannot physically deliver full rated thrust and it has to pull back.

Quoting Fabo (Reply 28):
I understand that in case of 777 with very light load, Vmca at TO (as computed for D-TO as I understand) could lead to values too high? Whereas with TO-1/2/x Vmca is actually computed for derated thrust? Do I understand this right?

Yes. TO-1/TO-2 are fixed derates...they make the engine behave as if you installed a lower thrust engine and Vmca drops as a result. D-TO (and D_TO1 and D-TO2) allow the crew, at any time, to advance the throttles to bypass the ATM part of the thrust reduction, so you have to calculate Vmca as if you didn't have the ATM in there.

Quoting Fabo (Reply 28):
As a sidenote, if I were to get a 777, throw everything out, including seats, upholstery, non-essential wiring, basicaly anything not fundamentaly required, minimum fuel and most powerful engine variant available, could I theoreticaly get into a situation that even a 25% derate would not let me depart as it would lead to a V2

No. V2 is just single engine climb-out speed, it will never be lower than Vmca (it could be equal).

Quoting Fabo (Reply 28):
Quoting BoeingGuy (Reply 27):
So that's why an Assumed Temperature Derate reduces thrust.

Would the actual limiting factor in real temperature be EGT?

Yes.

Tom.
 
Rara
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RE: Reduced Versus Full Takeoff Thrust

Fri Nov 04, 2011 3:25 pm

Quoting BoeingGuy (Reply 27):
Quoting tdscanuck (Reply 30):

No. The aircraft needs exactly the same thrust regardless of outside temperature. The issue is how hot the engine has to get to provide that required thrust. At very high temperatures the engine cannot physically deliver full rated thrust and it has to pull back.

Thanks to you both! Now I get it. I was always under the impression that high temperatures somehow prevented engines from packing the full force into the air, so to speak.   I see now that it is really due to overheating. Cheers!
Samson was a biblical tough guy, but his dad Samsonite was even more of a hard case.
 
Mir
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RE: Reduced Versus Full Takeoff Thrust

Fri Nov 04, 2011 5:44 pm

Quoting Rara (Reply 31):
I was always under the impression that high temperatures somehow prevented engines from packing the full force into the air, so to speak.

This isn't wrong - high temperatures (and the resulting thinner air) do make it more difficult for the engine to produce thrust. Thus the requirement for the engine to work harder, and thus the running up against limitations.

-Mir
7 billion, one nation, imagination...it's a beautiful day
 
BoeingGuy
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RE: Reduced Versus Full Takeoff Thrust

Fri Nov 04, 2011 6:45 pm

Quoting tdscanuck (Reply 30):
Yes. TO-1/TO-2 are fixed derates...they make the engine behave as if you installed a lower thrust engine and Vmca drops as a result. D-TO (and D_TO1 and D-TO2) allow the crew, at any time, to advance the throttles to bypass the ATM part of the thrust reduction, so you have to calculate Vmca as if you didn't have the ATM in there.

On Seattle Boeing airplanes, the autothrottle sets the actual thrust lever position lower for TO-1 or TO-2. So you could override it and command full underated thrust by pushing the thrust levers forward (or pushing the TO/GA switch also removes the derate). However since all the V speeds, including Vmca are calculated as if TO-1 or TO-2 were the actual maximum trhust of the engine (as tdscanuck has noted) pilot are prohibited from doing that unless you are in a real emergency like ground contact is imminent.

But yeah, if you are doing a combined fixed and assumed temperature derate that would make it hard for the pilot in the heat of the moment. It's okay to push the throttles forward to remove the assumed temperature portion of the derate, but not the fixed derate part. Well, how's he or she going to figure that out?

From what I understand the 717s fixed derate actually kind of resets the scale of the thrust levers, so to speak, and puts the throttles exactly where they would be if doing a full thrust takeoff. That same throttle position now just corresponds to the derated thrust. The derate is done behind the scenes. So you couldn't advance the throttles to remove the derate. "Boeing North" airplanes actually just set the thrust levers back a little where they'd be for the lower derated thrust. Not sure if I'm explaining this clearly.

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