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convair880mfan
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At what height above field elevation is takeoff thrust reduced [increased] to climb thrust

Mon Aug 02, 2021 8:47 pm

I have heard 1000 feet agl and 1500 ft agl from pilots. A former TWA Boeing 707 pilot told me that in his time 800 feet agl was when they reduced thrust and leveled off to build speed for flap retraction.

A now retired 747 captain told me that on that aircraft, one needed to fly level for a time to build speed for flap retraction and that at heavy gross weights it was rare to be able to climb initially and retract flaps at the same time.

Are there many commercial airliners that can retract flaps in a climb or is it related to weight and other conditions?. I have no idea.

Thanks to one and all for your responses.
 
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BWIAirport
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Re: At what height above field elevation is takeoff thrust reduced [increased] to climb thrust

Mon Aug 02, 2021 8:56 pm

I've only flown on simulators (PMDG products, etc) but in my experience it's around where you mentioned, certainly below 2000ft. As you alluded to, there are variables to this such as aircraft weight and noise restrictions at the departure airport. Someone correct me if I'm wrong but the cost index or climb/cruise profile may contribute as well.
 
Nicoeddf
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Re: At what height above field elevation is takeoff thrust reduced [increased] to climb thrust

Mon Aug 02, 2021 9:16 pm

convair880mfan wrote:
I have heard 1000 feet agl and 1500 ft agl from pilots. A former TWA Boeing 707 pilot told me that in his time 800 feet agl was when they reduced thrust and leveled off to build speed for flap retraction.

A now retired 747 captain told me that on that aircraft, one needed to fly level for a time to build speed for flap retraction and that at heavy gross weights it was rare to be able to climb initially and retract flaps at the same time.

Are there many commercial airliners that can retract flaps in a climb or is it related to weight and other conditions?. I have no idea.

Thanks to one and all for your responses.


If not obstacle limited, it is 1000ft AGL for NADP2 and 3000ft AGL for NADP1, respectively.

Most of the times though, there is barely a real world change in thrust, due to take off derate.
 
convair880mfan
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Re: At what height above field elevation is takeoff thrust reduced [increased] to climb thrust

Mon Aug 02, 2021 9:18 pm

NADP1? NAPD2? Sorry I don't know the meaning of these?
 
Okcflyer
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Re: At what height above field elevation is takeoff thrust reduced [increased] to climb thrust

Mon Aug 02, 2021 9:38 pm

On many aircraft, there can be a thrust INCREASE transitioning from derated takeoff thrust to climb thrust (usually also derated)
 
ChrisKen
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Re: At what height above field elevation is takeoff thrust reduced [increased] to climb thrust

Mon Aug 02, 2021 9:39 pm

convair880mfan wrote:
NADP1? NAPD2? Sorry I don't know the meaning of these?

Noise Abatement (Departure) Procedures - 1 Areas close to airport. 2 Further away ~25kms
 
GalaxyFlyer
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Re: At what height above field elevation is takeoff thrust reduced [increased] to climb thrust

Mon Aug 02, 2021 10:02 pm

Quads tend to have less excess thrust on take-off than twins, so twins often can reduce to climb thrust and maintain a heathy climb rate. Remember they both have to fly with ONE engine inoperative, so the twin has lots of excess on a AEO take-off.
 
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tb727
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Re: At what height above field elevation is takeoff thrust reduced [increased] to climb thrust

Tue Aug 03, 2021 1:06 am

Okcflyer wrote:
On many aircraft, there can be a thrust INCREASE transitioning from derated takeoff thrust to climb thrust (usually also derated)


We had FE's giving us numbers on the 727 when light that would show an addition of thrust at 1000', at which point we said you don't reduce takeoff thrust below your climb thrust.

It's funny on the Airbus I call it a climb thrust takeoff when we are pretty light, especially on the 319's. I've seen some FO's will try to be all smooth bringing the thrust lever from FLX/MCT to CLB slowly as to have a smooth thrust change when there isn't even a difference.
 
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Starlionblue
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Re: At what height above field elevation is takeoff thrust reduced [increased] to climb thrust

Tue Aug 03, 2021 1:16 am

In our case, the thrust reduction and acceleration altitudes are typically both 1500ft AAL.

Nose down. Reduce thrust to the CLB detent. Accelerate and clean up. Maintain green dot (max L/D ratio until 3000ft. Basically NADP2.

Some airports have different procedures, which require variation of thrust reduction and/or acceleration altitude.

convair880mfan wrote:
NADP1? NAPD2? Sorry I don't know the meaning of these?


NADP1
Image

NADP2
Image
 
Woodreau
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Re: At what height above field elevation is takeoff thrust reduced [increased] to climb thrust

Tue Aug 03, 2021 3:29 am

When you run your performance numbers for the airport and specific runway, the takeoff performance report will tell you what your thrust reduction and AEO/TEO (all engines operating / two engines) and OEI (one engine inoperative) acceleration altitudes are for that one specific takeoff you are doing.

Normally, our airline does thrust reduction and acceleration at 1000ft AFE.

However at one airport, thrust reduction is at 1000ft AFE, and acceleration is at 3000ft AFE. At another airport, thrust reduction is at 800ft AFE, and acceleration is at 3000ft AFE.
 
CanukinUSA
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Re: At what height above field elevation is takeoff thrust reduced [increased] to climb thrust

Tue Aug 03, 2021 3:42 am

There are a lot of variables that may affect where a pilot reduces to climb thrust: (Sorry if this adds to your confusion over thrust reduction altitude)
1) How long the engines may be operated at takeoff thrust. All Engines are certified for 5 minutes at takeoff thrust. Many Engines now are approved to use takeoff thrust for 10 minutes in the event of an engine failure to improve climb performance. Since Engine life is typically affected by the time spent at high thrust levels, most airlines will try to reduce thrust during takeoff and the reduce to climb power as soon as they can legally and safely. It depends on the aircraft weight, runway length, elevation. temperature, air pressure and if there are obstacles present on the departure path. Larger airlines have Aircraft Performance Engineers that will do takeoff calculations and specify a Thrust reduction altitude to optimize Aircraft Performance and Engine Life. For smaller airlines and Business Jets because they do not have aircraft performance engineers and the flight crew typically do the takeoff performance calculations, they use procedures for reducing thrust in accordance with the FAA Aircraft Certification Standards, so they typically use 1500 feet above airfield elevation as that is what the FAA has the takeoff and climb out profile up to in the Aircraft Certification Regulations for Transport Category Aircraft.
2) Noise restrictions at many airports as demonstrated in the post above may require thrust reduction at particular locations to keep the noise level down over noise sensitive areas. The Noise Abatement procedures shown in the previous post were developed by International Civil Aviation Organization (ICAO) to standardize Noise Abatement procedures worldwide so that a million different procedures do not get developed in different countries, but some countries may decide to have procedures that differ from the ICAO standard ones.
 
Max Q
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Re: At what height above field elevation is takeoff thrust reduced [increased] to climb thrust

Tue Aug 03, 2021 4:56 am

Disregarding certain airports special departure procedures there are two types of noise abatement departures :


ICAO ‘A’ - Take off thrust is maintained to 1500’ AGL then reduced to climb thrust, and speed maintained, acceleration (with flap retraction) to clean maneuvering speed then cleared speed starts at 3000’ AGL, this procedure is more commonly used outside the US



ICAO ‘B’ - Take off thrust maintained to 1000’ AGL then reduce to climb power, accelerate to clean maneuvering (with flap retraction) maintain clean maneuvering to 3000’ AGL then accelerate to 250 KIAS or cleared speed
 
e38
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Re: At what height above field elevation is takeoff thrust reduced [increased] to climb thrust

Tue Aug 03, 2021 1:54 pm

convair880mfan, if it helps to put the two noise abatement departure procedures (NADP) in context, in the U.S., NADP1 (ICAO A) is commonly referred to as the “Close-in Community Noise Abatement Departure Procedure” while NADP2 (ICAO B) is called “Distant Community Noise Abatement Departure Procedure.”

Normally, published flight operations directives dictate to the crew which procedure to use when departing an airport. Occasionally it may be different for different runways at the same airport.

e38
 
delta-flyer
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Re: At what height above field elevation is takeoff thrust reduced [increased] to climb thrust

Wed Nov 03, 2021 3:18 am

[twoid]I have often thought of this, but in my mind, I assumed that it’s based on the engine exhaust gas temperature reaching a certain percentage of the critical level. But the chart shows altitudes, so just out of curiosity, how close does the engine temperature get to critical during takeoff? [/twoid]
 
FlapOperator
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Re: At what height above field elevation is takeoff thrust reduced [increased] to climb thrust

Wed Nov 03, 2021 8:28 pm

delta-flyer wrote:
[twoid]I have often thought of this, but in my mind, I assumed that it’s based on the engine exhaust gas temperature reaching a certain percentage of the critical level. But the chart shows altitudes, so just out of curiosity, how close does the engine temperature get to critical during takeoff? [/twoid]


Most modern aircraft, as noted earlier, aren't anywhere close to engine limitations during the vast majority of operations.

Essentially, the risk is in operating engines at close to their limits, so flex takeoffs essentially "fool" the engine into thinking its hotter out, and operating at a lower power setting consistent with the one engine inoperative climb gradients required by regulation. This prolongs engine life, reduces noise and keeps engines away from their most likely failure points, like high heat or rotational limits.
 
Max Q
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Re: At what height above field elevation is takeoff thrust reduced [increased] to climb thrust

Wed Nov 03, 2021 10:43 pm

FlapOperator wrote:
delta-flyer wrote:
[twoid]I have often thought of this, but in my mind, I assumed that it’s based on the engine exhaust gas temperature reaching a certain percentage of the critical level. But the chart shows altitudes, so just out of curiosity, how close does the engine temperature get to critical during takeoff? [/twoid]


Most modern aircraft, as noted earlier, aren't anywhere close to engine limitations during the vast majority of operations.

Essentially, the risk is in operating engines at close to their limits, so flex takeoffs essentially "fool" the engine into thinking its hotter out, and operating at a lower power setting consistent with the one engine inoperative climb gradients required by regulation. This prolongs engine life, reduces noise and keeps engines away from their most likely failure points, like high heat or rotational limits.



Agree with all that except lower noise


With a reduced thrust take off your climb gradient will be shallower and keep the aircrafts noise closer to the ground for longer


As far as the effect on the local neighborhood you’re better off doing a full power take off with thrust cutback at 1000 or 1500 AGL


That gets you and your noise up and away from the ground as quickly as possible


Of course this is detrimental in terms of engine life
 
FlapOperator
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Re: At what height above field elevation is takeoff thrust reduced [increased] to climb thrust

Thu Nov 04, 2021 1:48 am

Max Q wrote:


Agree with all that except lower noise


With a reduced thrust take off your climb gradient will be shallower and keep the aircrafts noise closer to the ground for longer


As far as the effect on the local neighborhood you’re better off doing a full power take off with thrust cutback at 1000 or 1500 AGL


That gets you and your noise up and away from the ground as quickly as possible


Of course this is detrimental in terms of engine life


Noise is kind of odd and frankly more art and NIMBYism than hard science, in my experience. One thing I've noticed is the slow elimination of noise scoring feedback in North America, at least. So, there seems to be no real "independent" means of verification, just a kind of a "know it when the noise monitors hear it" thing. In Europe, it seems that track is the important element to noise adherence, as often departures will keep you relatively low to the ground as you snake away from the terminal area to an enroute climb scheme. In my aircraft track adherence for noise often requires a very slow departure speed (say 185 KIAS vs. a normal 250-260 KIAS) so for a noise over ground standpoint good, for a total footprint thing, maybe bad? I don't know.

The thing is that difference between max blast and min thrust might be the difference between 3-5% N1. A ton of value in the grand scheme of things cumulatively, even if we are talking at the margins at the point in time. For a data point like noise, I'd say really questionable to its total effect of the noise the last 10% of thrust made to total noise along track or airport footprint.

Like I said, super soft science, at best.
 
bluecrew
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Re: At what height above field elevation is takeoff thrust reduced [increased] to climb thrust

Fri Nov 05, 2021 7:00 am

FlapOperator wrote:
Max Q wrote:


Agree with all that except lower noise


With a reduced thrust take off your climb gradient will be shallower and keep the aircrafts noise closer to the ground for longer


As far as the effect on the local neighborhood you’re better off doing a full power take off with thrust cutback at 1000 or 1500 AGL


That gets you and your noise up and away from the ground as quickly as possible


Of course this is detrimental in terms of engine life


Noise is kind of odd and frankly more art and NIMBYism than hard science, in my experience. One thing I've noticed is the slow elimination of noise scoring feedback in North America, at least. So, there seems to be no real "independent" means of verification, just a kind of a "know it when the noise monitors hear it" thing. In Europe, it seems that track is the important element to noise adherence, as often departures will keep you relatively low to the ground as you snake away from the terminal area to an enroute climb scheme. In my aircraft track adherence for noise often requires a very slow departure speed (say 185 KIAS vs. a normal 250-260 KIAS) so for a noise over ground standpoint good, for a total footprint thing, maybe bad? I don't know.

The thing is that difference between max blast and min thrust might be the difference between 3-5% N1. A ton of value in the grand scheme of things cumulatively, even if we are talking at the margins at the point in time. For a data point like noise, I'd say really questionable to its total effect of the noise the last 10% of thrust made to total noise along track or airport footprint.

Like I said, super soft science, at best.

You're both right - it does definitely increase noise because of the longer takeoff and climb phase, especially if your aircraft does a derate on the climb.
But, this is also why we have new-ish RNAV procedures at seemingly every noise sensitive airports to avoid those areas. Unfortunately... unless there's water, it's usually the poor parts of the city. On RNAV tracks for noise, typically you can easily hit RNP compliance at 210 or greater, unless there's real sharp turns. In BOS you can do the whole departure accelerating normally to 250.

To me it's super telling that all the noise monitoring airports, all the mandatory NA programs like FlyQuiet, etc., seem to be around the super wealthy areas near airports. We're happy to have any number of airplanes and an unlimited number of APUs spinning around a rural poor neighborhood near Memphis, but as soon as it affects Newport Beach, CA, that's a bridge too far. The NIMBY problem doesn't seem to be going away, either. Airplanes get quieter and quieter, noise complaints continue to increase, and homebuilders keep buying the cheap seats at the end of runways and building homes there (See: Denver).

For the OP: unless specified somewhere else, it's a 1000AGL transition from TO thrust to CLB, and then you also start accelerating and retracting flaps on schedule, at least at my operator in the US. In the US this, to my knowledge, is the rule not the exception: I don't know of any carrier that has a different policy.
 
seven47
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Re: At what height above field elevation is takeoff thrust reduced [increased] to climb thrust

Sat Nov 06, 2021 11:36 am

On the 747 Classic (-100/‐200), we would select a vertical speed between 200 and 500 feet per minute to get enough acceleration for flap retraction when we were heavy. If we were flying out of the Middle East in the summer, we often had to completely level off to accelerate for cleanup.
 
seven47
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Re: At what height above field elevation is takeoff thrust reduced [increased] to climb thrust

Sat Nov 06, 2021 11:37 am

On the 747 Classic (-100/‐200), we would select a vertical speed between 200 and 500 feet per minute to get enough acceleration for flap retraction when we were heavy. If we were flying out of the Middle East in the summer, we often had to completely level off to accelerate for cleanup.

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