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Engine De-rate

Wed Aug 15, 2012 3:07 pm

Dear All,

Can anyone tell me how much I can expect to extend the expected engine life between shop-visits by using 15% or 20% de-rate as opposed to 10%?

Thanks, Sveinn.
Nothing compares to taking off in an empty 757 with full thrust!
Posts: 815
Joined: Fri Sep 07, 2001 1:38 am

RE: Engine De-rate

Wed Aug 15, 2012 5:07 pm

I found some goodies for you, take a look;

Rolls Royce on derating:

The Operator Benefits Of Climb Derate
As a rule of thumb, if the average time weighted climb derate achieved in operation
is 5%, then Rolls-Royce estimates that this will typically result in 3% more time-onwing
to full refurbishment compared to using maximum climb thrust all the time
(although other factors such as takeoff derate, stage length, harshness of operation,
etc., also have an effect).
Three percent more time on wing to full refurbishment is equivalent to 3% reduction
in Direct Maintenance Cost (DMC) per engine flying hour, so climb derate can offer
some significant savings if used consistently.
As previously shown in section 2, the block fuel increase is very small; in the CLB 1
Slow example in Figure 9 the value was $9 per trip. Assuming 700 trips per year the
cost of the increased fuel is $6,300 per aircraft per year, but the DMC savings due to
5% achieved climb derate could typically be 10 times this per aircraft per year.

Airbus on derating:

The severity factor for a one hour flight is 1.6 with no derate and 1.2 with 10% derate, which represents a 30% decrease therefore: Shop visit rate improvement = 0.9% x 30% = 0.27... etc etc, this from a 1984 'airbus technical digest'

Some old Mil-reports on life extension, which don't mention derating, but interesting nonetheless:

And finally, an old thread:
How To De-rate An Engine (by Liamksa Nov 8 2003 in Tech Ops)

Thanks for giving me something fun to research - more interesting than work  
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Posts: 8572
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RE: Engine De-rate

Wed Aug 15, 2012 5:20 pm

Quoting SRQKEF (Thread starter):
Can anyone tell me how much I can expect to extend the expected engine life between shop-visits by using 15% or 20% de-rate as opposed to 10%?

It depends what's driving your shop visits; if it's happening because you're hitting the limits on the life-limited parts, then it won't save you any time. If it's happening because of EGT degradation then you'll see some benefit (but it will depend a lot on which derates you're using and what the original thrust rating is).


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