B737 improved climb

[fruitbatflyer]

I would be interested in opinions on the use of improved climb at lower weights to further reduce takeoff thrust.
Obviously I am talking about long, dry and smooth runways, no tailwind etc.
As I see it, if you can use it at high weight for a given set of conditions to squeeze extra payload, why not use it at lower weights to help with engine life and to enjoy greater margins above VMC and minimum certified climb gradients if it does go wrong? I reiterate, on sufficiently long and suitable runways of course. What is your company policy and your own opinion? Do you practice rejected takeoffs using the higher speeds on regular simulator sessions and if so, do many pilots end up over running?
Or is improved climb really only there for max payload when the lower speeds won't give it to you?

[mutt]

If you decided to use Boeings or Airbus Optimized V-speed philosophies you will find that you are using improved climb most of the time.

For the more generally used Boeing method of balanced field calculations, you should already have the ability to reduce your takeoff thrust using Fixed Derates and an extended environmental envelope up to 69C. This should provide you with approx a 35% thrust reduction.

Before you initiate an improved climb policy to enhance engine savings, I would ask your engine manufacturer to quantify the savings associated with getting the full 35% thrust reduction.

IMHO I believe that you will find that crews hate higher V1 speeds but will not be too concerned about increasing the speed margins above VMC and the climb gradient.

Mutt.

[calypso]

I thought the max derate was 25%.

[RAT 5]

General concensus, that I've come across, in UK is that improved climb is only used to increase MTOW if required. It is not used to obtain extra tanking fuel etc. etc.

I was taught that taking the 'top end' off the temp. was what mattered with engine life. Taking further dribbles off will do nothing other than make life difficult. It would possibly increase cost by asking the performance suppliers to provide the extra data in what they would consider to be a non-standard application.

It seems to go against the valuable KISS principle.

[High Volt]

RAT 5

Spot on! Top end temps are where the blade creep/wear affects the turbine most: or that at least is how I understand it. You can be too clever in this game if you're not careful. Indeed KISS.

[mutt]

I thought the max derate was 25%.

This is the maximum allowed thrust reduction Off the engine RATING, we can operate engines with two fixed derate ratings, DER1 @ -10% and DER2 @ -20%.

By applying the two types of thrust reductions, you can therefore end up operating a light B744 using a 45% thrust reduction.

I didnt mention DER2 for the B737 as i dont know if they have the 2nd option.

Mutt.

[john_tullamarine]

Reading a 737 manual the other day for an operator whose details I didn't know previously, there was reference to two levels of derate.

[DontSink]

fruitbatflyer,

I`ve never heard of that procedure! If it`s not written, don`t do it! To spare engine time, VMCs, etc..., has you said, you already have the reduced thrust takeoff with the assumed temperature.

Improoved climb is always a last resorce when 2nd segment climb limited, but long runway available! It is also wise to use improoved climb with the next flap setting when windshear has been reported. Also improoved climb reduces tyre life!

Cheers

[mutt]

I`ve never heard of that procedure!

I guess that you have never flown an Airbus....... or even a Boeing using optimized V-speeds...........

Happens all the time.\


Mutt.

[fruitbatflyer]

Thanks all. Mutt, you pretty well confirm my thoughts - that crews hate higher V1 speeds and therein lies most resistance to using improved climb when it is presented as an alternative set of numbers. However, when it is hidden by virtue of a single set of optimised V-speed figures, they happily accept the concept without perhaps realising that Mr Boeing or Mr Airbus is looking after their best interests, both commercially and performance margin wise.
As for tyre wear, I hear this from time to time. As a cost in the big scheme of things, do tyres really wear out that much on takeoff as opposed to landing, and in any case would their value over ride the considerations of payload and engine life?