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

I think CLB is automatically selected to be less than TO, not the other way 'round.

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. :8

With long runways and light weights it's not uncommon to have takeoff power to be less than climb power. When climb power is selected the power advances(increases).

AB actually use "derate 2" for take off, which is less than climb thrust.
Flex thrust normally cannot be less than clb thrust, at least for all the aircraft I flew.

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.

That is an odd thing for the Captain to tell the passengers. :suspect:

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. :ugh:

' Cause it's not actually what is "Required" for climb, it's just what is programmed into the EEC or FADEC.

Why?

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.

...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

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 :rolleyes:
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 :cool: indeed feels odd, but that is what they want us to do.

B 737-800. CLB thrust is frequently more than T/O thrust.

Is your airline making any money?:E

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.

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. :eek:

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.

You use de-rate + assumed temperature with improved climb to save engines on the NG? We use A/C OFF or improved climb only when we can't get out with A/C Auto - not to save money by using less than full takeoff thrust(Classic).

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.