reduced power takeoffs?

[RUDAS]

i read that many operators opt for reduced-power takeoffs out of airports with long runways,and i read of a particular instance where,for example,a 777 took off with reduced power out of lhr's 27L,and for this,the crew assumed a temp outside of 43 degrees celsius.

Being a piston pilot,i'd like to know if anybody can explain the reasons for assuming such a high temp when executing reduced power takeoffs? technically,what does this imply?

thanks:ok:

[sickBocks]

A clever way of prolonging engine life ($$$) by fooling the engines into thinking the temperature is warmer than it is.

A concise explanation can be found here:

http://www.b737.org.uk/assumedtemp.htm

sB

[alexban]

Indeed ,a clever way to prolong engine life,but recently there are anallyses to determine if the increased climb time due to power reduction is not inducing bigger costs than the savings from power reduction.
:confused:

[TR4A]

recently there are analysis to determine if the increased climb time due to power reduction is not inducing bigger costs than the savings from power reductionAt my company we use max climb power. They say there is no savings using reduced climb.

[Yellow Sun]

Alexban wrote:

increased climb time due to power reduction is not inducing bigger costs than the savings from power reduction

Quite possible Alex', but I think you may be referring to the "Reduced Climb Thrust" option available on some aircraft, or possibly option to perform the takeoff (and climb) calculation using a selection of thrust ratings.

I don't know of any aircraft where a reduced thrust (Flex Thrust) takeoff will result in a required takeoff thrust setting below the scheduled climb thrust. If that were not the case then you would have a Thrust Increase Alt (TIA) instead of the normal Thrust Reduction Alt (TRA). But someone out there may know of an exception???

YS

[RUDAS]

Thanks sickBocks,that link was most useful!:ok: :ok:

[mutt]

Yellow Sun,

Check out some Airbus and Douglas aircraft and i believe that you will find the throttles advancing for climb power.


RUDAS,

We can apply fixed derates and assumed temperature derates to the GE90 on the B777, this brings the total power reduction to around 40% and the thing still climbs like a homesick angel. :)


Mutt.

[TR4A]

I don't know of any aircraft where a reduced thrust (Flex Thrust) takeoff will result in a required takeoff thrust setting below the scheduled climb thrust. If that were not the case then you would have a Thrust Increase Alt (TIA) instead of the normal Thrust Reduction Alt (TRA). But someone out there may know of an exception???We use 20K and 18K derate on our B737-700's which means when we set max climb power it IS a throttle increase.

[Yellow Sun]

TR4A

We use 20K and 18K derate on our B737-700's which means when we set max climb power it IS a throttle increase.


Thanks for that, so can anyone explain why you should takeoff with a lower thrust setting than that which you intend to use for the subsequent climb.

YS

[mutt]

Different ratings with different goals. There is a crew idea that the throttles should come back for climb power, however there is no law nor technical reason why they should. You have finished the takeoff phase and moving into a new phase, you use the power required for that phase......


Mutt.