B738 increased thrust after liftoff?
Thread Starter
Join Date: Jun 2009
Location: beirut!
Age: 29
Posts: 17
Likes: 0
Received 0 Likes
on
0 Posts
B738 increased thrust after liftoff?
Please help an observant youngster here...
Flew with AB with their 738s some days ago and noticed something i really never experienced before... Say about 30 seconds after liftoff the engine power increased notable... It did the same on the outbound leg too...
Why? I thought that T/O thrust never could get below CLB?
Thank you,
BP
Flew with AB with their 738s some days ago and noticed something i really never experienced before... Say about 30 seconds after liftoff the engine power increased notable... It did the same on the outbound leg too...
Why? I thought that T/O thrust never could get below CLB?
Thank you,
BP
Bottums Up
On the b717 when Using Flex takeoff powers, if one flexes over about 50 degrees C, then takeoff power will be less than climb power, so once the aircraft passes through the acceleration altitude, power is increased to climb power setting.
I agree with you, if feels and sounds weird.
I agree with you, if feels and sounds weird.
Thread Starter
Join Date: Jun 2009
Location: beirut!
Age: 29
Posts: 17
Likes: 0
Received 0 Likes
on
0 Posts
Okey, interesting. Thanks for your replies.
The captain told us during the climb that our TOW was 55T...Runway length 4000m...
So yeah, the ''light weight'' could explain it.
The captain told us during the climb that our TOW was 55T...Runway length 4000m...
So yeah, the ''light weight'' could explain it.
Bottums Up
Originally Posted by aviatorhi
Maybe it's common sense kicking in but why on earth anyone would set do a takeoff at a power setting which is less than that required for climb is beyond me.
The company produces manufacturer endorsed performance figures, that allow a certain level of flex (assumed temperature) power (haven't used de-rate so can't comment) which meet the takeoff performance requirements, for the given runway, atmosphere and gross weight.
Join Date: Jun 2002
Location: Wor Yerm
Age: 68
Posts: 4
Likes: 0
Received 0 Likes
on
0 Posts
...and on an Embraer when using Take Off 2 or 3. Someone did some difficult sums some time ago and calculated that using the highest possible climb power would save us a fortune in fuel. And according to recent feedback, the sums were right.
PM
PM
Join Date: Apr 2002
Location: FUBAR
Posts: 3,348
Likes: 0
Received 0 Likes
on
0 Posts
Current company uses min (determined by EFB ) take-off thrust possible, often DeRate 2 (22k from a 27k engine) & max assumed temp , + improved climb, so take-off N1 = something close to high idle 
However. . .this is purely to preserve engine life & apparently power setting after airborne has no detrimental effect on eng life. So given the most economical in fuel burn is to use full climb thrust (if continous climb expected) to shorten time in climb , it goes like this. . . . . . .
Take off at derate 2/55c or whatever . . 800' full climb thrust
indeed feels odd, but that is what they want us to do.
However. . .this is purely to preserve engine life & apparently power setting after airborne has no detrimental effect on eng life. So given the most economical in fuel burn is to use full climb thrust (if continous climb expected) to shorten time in climb , it goes like this. . . . . . .
Take off at derate 2/55c or whatever . . 800' full climb thrust
indeed feels odd, but that is what they want us to do.
Last edited by captplaystation; 19th Sep 2012 at 12:29.
Join Date: Apr 2010
Location: Home soon
Posts: 0
Likes: 0
Received 0 Likes
on
0 Posts
Current company uses min (determined by EFB ) take-off thrust possible, often DeRate 2 (22k from a 27k engine) & max assumed temp , + improved climb, so take-off N1 = something close to high idle
Join Date: Mar 2001
Location: I wouldn't know.
Posts: 4,497
Likes: 0
Received 0 Likes
on
0 Posts
AB uses user selected full climb thrust if a unrestricted climb is likely. Independent of take off reductions full climb thrust is therefore the normal thing and that is indeed nearly always a thrust increase at climb thrust reduction altitude (1000' AGL). Nowadays it feels weird to experience a real climb thrust reduction, for example when deadheading on the airbus fleet.
Join Date: Jan 2006
Location: US
Posts: 2,205
Likes: 0
Received 0 Likes
on
0 Posts
Lots of airplanes have reduced climb power also. CLB 1 or CLB 2 are both less than regular CLB power. CLB 2 is in the range of 10-15% less than CLB power.
CLB power uses less fuel getting to altitude but the tradeoff is a higher EGT.
And the a/c that use the lowest power of the multiple engine 'choices' along with flex/derated power takeoff with a power setting that's about the same as cruise power.
CLB power uses less fuel getting to altitude but the tradeoff is a higher EGT.
And the a/c that use the lowest power of the multiple engine 'choices' along with flex/derated power takeoff with a power setting that's about the same as cruise power.
Join Date: Mar 2001
Location: I wouldn't know.
Posts: 4,497
Likes: 0
Received 0 Likes
on
0 Posts
That is true for the 738 as well, however the pilots can always user select the full climb thrust regardless. And that is exactly what AB, and apparently cptplaysations outfit as well, do. According to Boeing and CFM it has no negative impact on engine life and saves some fuel which accumulates to several million Euro a year quite fast.
Join Date: Apr 2010
Location: IRS NAV ONLY
Posts: 1,230
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by captplaystation
Current company uses min (determined by EFB ) take-off thrust possible, often DeRate 2 (22k from a 27k engine) & max assumed temp , + improved climb, so take-off N1 = something close to high idle
Join Date: Feb 2003
Location: UK
Posts: 272
Likes: 0
Received 0 Likes
on
0 Posts
I fly the 737-800. We always derate and use an assumed temperature if possible and this automatically selects a reduced climb 1 or climb 2 thrust. Unlike other contributors however, my airline wants us to leave the reduced climb thrust in as apparently it does save engine life (at the expense of increased fuel burn) and with our lease agreement, increased engine time on wing saves far more money than the increased fuel burn costs.
Join Date: Feb 2006
Location: UK
Posts: 112
Likes: 0
Received 0 Likes
on
0 Posts
Use of reduced thrust:
On T/O: Reducing T/O thrust, significantly reduces engine wear, keeps greater EGT margins long term- keeps the specific engine operating more efficient.
On climb: CFM/Boeing say fuel savings, climbing at full thrust outweighs long term engine wear.
-----
CLB = full trust for the climb
CLB1 = an approx 10% derate of thrust (3% N1), (gradually increasing up to full thrust at approx 12000' i think)
CLB2 = an approx 20% derate of thrust (6% N1), (gradually increasing up to full thrust at approx 15000´ i think)
Also the aircraft "should" be preprogrammed so that Climb thrust does not exceed T/O thrust unless selected on CDU N1 page.
So to save the company money, reduce thrust as much as possible for T/O and climb at full thrust once above acceleration height if you are expecting unrestricted climb to above 12-15000'
On T/O: Reducing T/O thrust, significantly reduces engine wear, keeps greater EGT margins long term- keeps the specific engine operating more efficient.
On climb: CFM/Boeing say fuel savings, climbing at full thrust outweighs long term engine wear.
-----
CLB = full trust for the climb
CLB1 = an approx 10% derate of thrust (3% N1), (gradually increasing up to full thrust at approx 12000' i think)
CLB2 = an approx 20% derate of thrust (6% N1), (gradually increasing up to full thrust at approx 15000´ i think)
Also the aircraft "should" be preprogrammed so that Climb thrust does not exceed T/O thrust unless selected on CDU N1 page.
So to save the company money, reduce thrust as much as possible for T/O and climb at full thrust once above acceleration height if you are expecting unrestricted climb to above 12-15000'