Reduced Thrust B737-200(Performance)Question
Thread Starter
Join Date: Feb 2005
Location: TANZANIA
Posts: 163
Likes: 0
Received 0 Likes
on
0 Posts
Reduced Thrust B737-200(Performance)Question
Hi
I have a question, this is for a B737-200.
Sometimes when weight for take-off is low , we reduced thrust until to the actual weight , e.g. a take-off at 26C reduced to almost 43C and then we read the speeds and EPR required at 43C
Now someone decides to take speeds at actual weight but take-off EPR is measured as average, that is in between 26C to 43C , somewhere in between, around 32C .
Its claimed that rotation is much earlier this way and its helpful for rough runways, now Im asking , is this true ?
Do you get airborne earlier if EPR is higher than whats shown on actual weight ?
Zenj
I have a question, this is for a B737-200.
Sometimes when weight for take-off is low , we reduced thrust until to the actual weight , e.g. a take-off at 26C reduced to almost 43C and then we read the speeds and EPR required at 43C
Now someone decides to take speeds at actual weight but take-off EPR is measured as average, that is in between 26C to 43C , somewhere in between, around 32C .
Its claimed that rotation is much earlier this way and its helpful for rough runways, now Im asking , is this true ?
Do you get airborne earlier if EPR is higher than whats shown on actual weight ?
Zenj
it seems you're using a thrust value for a lower assumed temp therefore you have more thrust---I may have misunderstood the question though?
also remember during a reduced thrust take off the wings are still working at the lower DA so that = better performance at times
a few questions,
Could you show please a sample AFM calculation?
What limitation comes up climb segments/ field lengths just interested?
also remember during a reduced thrust take off the wings are still working at the lower DA so that = better performance at times
a few questions,
Could you show please a sample AFM calculation?
What limitation comes up climb segments/ field lengths just interested?
Join Date: Aug 2006
Location: USA
Posts: 142
Likes: 0
Received 0 Likes
on
0 Posts
I think what we are being asked about is "assumed temperature" method of calculating take off performance.
In your sample if the data supports a 43 degree day assummed temp and the power is set for this condition the takeoff will be very close to a 43 degree day takeoff.
Now you confuss me a bit. If the runway condition is poor and the Captain want to spend less time on the runway reducing the assummed temperature will reduce the take off roll. The trust would be set for this new assumed temperature.
The advantages of using assumed temperature,
- less likely to experience and engine failure, because of placeing less demand on the engine. (less rpm and turbine temperature, longer engine life, better economics..)
- if the engine fails, before or after V1, it is an easier aircraft to control, less rudder or wing into the failed engine, I like this reason best!
Remember assumed temperature still gives the crew all the perfomance to stop or continue at that critical before/after V1. Some companies will even add an additional margin. The other common factor is fixing the assumed temperature limit, by either a fixed degree, say 48C or a maximum of 25 degrees over actual temperature.
Safety is paramount and this method increase both safety and operating efficiencies.
Hope I helped,
In your sample if the data supports a 43 degree day assummed temp and the power is set for this condition the takeoff will be very close to a 43 degree day takeoff.
Now you confuss me a bit. If the runway condition is poor and the Captain want to spend less time on the runway reducing the assummed temperature will reduce the take off roll. The trust would be set for this new assumed temperature.
The advantages of using assumed temperature,
- less likely to experience and engine failure, because of placeing less demand on the engine. (less rpm and turbine temperature, longer engine life, better economics..)
- if the engine fails, before or after V1, it is an easier aircraft to control, less rudder or wing into the failed engine, I like this reason best!
Remember assumed temperature still gives the crew all the perfomance to stop or continue at that critical before/after V1. Some companies will even add an additional margin. The other common factor is fixing the assumed temperature limit, by either a fixed degree, say 48C or a maximum of 25 degrees over actual temperature.
Safety is paramount and this method increase both safety and operating efficiencies.
Hope I helped,
Thread Starter
Join Date: Feb 2005
Location: TANZANIA
Posts: 163
Likes: 0
Received 0 Likes
on
0 Posts
Thanks guys for your input.
What you have said is correct and makes sense.
What my question was , instead of reducing to actual weight prevailing , e.g. at 43C read speeds and EPR , someone reads speeds on 43C ( thats were actual weight is ) but instead of taking EPR also from 43C column of which we all do , he takes somewhere halfway between 43C and where it gives max thrust ( actual temp column).
They say this procedure gives early lift-off ( good for rough runways ) .
I have not seen this in performance books , so im asking is it true that it gives early lift-off ?
Is it a common procedure anywhere ?
Zenj
What you have said is correct and makes sense.
What my question was , instead of reducing to actual weight prevailing , e.g. at 43C read speeds and EPR , someone reads speeds on 43C ( thats were actual weight is ) but instead of taking EPR also from 43C column of which we all do , he takes somewhere halfway between 43C and where it gives max thrust ( actual temp column).
They say this procedure gives early lift-off ( good for rough runways ) .
I have not seen this in performance books , so im asking is it true that it gives early lift-off ?
Is it a common procedure anywhere ?
Zenj
Join Date: Oct 2005
Location: in them thar hills
Posts: 264
Likes: 0
Received 0 Likes
on
0 Posts
Yes, more thrust (greater EPR) for a given weight will accelerate the airplane to V1 more rapidly, so in that regard it is a quicker liftoff in less distance than is the case at the minimum allowed EPR (assumed temperature method). However, if he is that bothered by the prevailing conditions, he should be using max thrust and considering a bleeds off takeoff as well, maybe with a greater flap setting to alleviate the effects of the rough runway. More flap = lower V1 and faster acceleration to that V1, less distance on runway, but suffers a climb penalty after takeoff and a longer 3rd segment.
If the company has some SOP like you describe, it should be in your FCOM and everyone should know it and use it.
It should not be his place to just dream up some pet procedure and force it on you.
If the company has some SOP like you describe, it should be in your FCOM and everyone should know it and use it.
It should not be his place to just dream up some pet procedure and force it on you.
Thread Starter
Join Date: Feb 2005
Location: TANZANIA
Posts: 163
Likes: 0
Received 0 Likes
on
0 Posts
Thanks gas-chamber for nice and precise answer.
I see my first officers , some few of them doing it and they say they were trained by their instructors, well I found out it's a practice done by one of the instructors.
As you said it. if its not in SOPS its not a standard !
Z
I see my first officers , some few of them doing it and they say they were trained by their instructors, well I found out it's a practice done by one of the instructors.
As you said it. if its not in SOPS its not a standard !
Z
