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engine to a specified condition.
Finally, reduced thrust on a given takeoff reduces stress level and likelihood of
an engine failure on that takeoff.
99
Flight Operations Support
10 September 2005
CFM PROPRIETARY INFORMATION
Subject to restrictions on the cover or first pa ge
EGT
N1
FLAT RATED THRUST
Thrust
(TOGA)
OAT
CP*
ISA+15°C
EGT RED LINE
* CP: Corner Point or Flat Rated Temperature
Reduced TTaakkeeOffff TThhrruusstt
Lower Takeoff EGT
Full rated 25% reduced
thrust thrust D%
Thrust (lbs) 26,218 19,663 -25
N1 (rpm) 5,061 4,509 -10.9
N2 (rpm) 14,968 14,490 -3.2
EGT (oC) 870o 752o -13.6
PS3 (psia) 482 377 -21.8
CFM56-5B/P 5B3 Engine Parameters
(Full Versus Reduced Thrust)
At Sea Level, Flat Rate Temperature of 30oC, 0.25 Mach, Typical New Engine
100
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CFM PROPRIETARY INFORMATION
Subject to restrictions on the cover or first pa ge
Reduced TTaakkeeOffff TThhrruusstt
EGTMargin and SFC deterioration vs Thrust Rating
Increasi ng
EGT
Deteriorati on
Rate
EGT Deterioration
SL Static Takeoff Thrust Rating Increasi ng
Increasi ng
FF
Deteriorati on
Rate
Fuel Flow Deteriorati on
SL Static Takeoff Thrust Rating Increasi ng
Although we do not have empirical
data to allow us to plot EGTM/SFC
deterioration or Cycles to Shop Visit
versus derate , we do know that for
different thrust ratings of the same
engine model the deterioration rate
tends to be greater on the higher
thrust ratings. This concept is shown
in the above and across charts.
Increasi ng
Cycles to
Shop Visit
Cycles to Shop Visit
SL Static Takeoff Thrust Rating Increasi ng
101
Flight Operations Support
10 September 2005
CFM PROPRIETARY INFORMATION
Subject to restrictions on the cover or first pa ge
2.0 4.0
1.6
1.2
0.8
0.4
0
Severity
Factor
Flight Length - Hours
01
0
20
% Effective Derate*
(Effective Derate* = Partial Takeoff % + Partial Climb % + Partial Cruise %)
0 10 20 30
1-Hour Flight Length
Takeoff
Climb
Cruise
Partial
Derate*
(%)
16
12
8
4
Operational Derate* (%)
0 10 20 30
3-Hour Flight Length
Takeoff
Climb
Cruise
Operational Derate* (%)
16
12
8
4
• Severity of operation is a
function of flight length and
“effective derate*” which is a
composite of takeoff, climb and
cruise reduced thrust/derate.
• T/O is weighted heavier on
shorter flights; climb and cruise
derate are weighted heavier
(relative to takeoff) on long
flights.
• This visualization is not used in
the pricing of maintenance
service contracts.
Severity Analysis
*Reduced Thrust
A means of quantifying and predicting mission severity based on how the engine is used
Reedduucceedd TTaakkeeOffff TThhrruusstt
102
Flight Operations Support
10 September 2005
CFM PROPRIETARY INFORMATION
Subject to restrictions on the cover or first pa ge
Estimated Severity Reduction Due
to the Use of Reduced Climb Thrust
Estimated
Severity
Reduction -
%
2-Hour Flight Leg
Takeoff Derate = 10%
Cruise Derate = 10%
Average Climb Derate Thrust - %
0 5 10 15 20 25
Takeoff
Climb
Severity Analysis
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This chart shows that the impact of climb thust reduction on severity, while still positive, is not as great as for
takeoff thrust reduction.
Although climb thrust reduction may reduce engine severity, its use may actually increase fuel burn on a given
flight because of the lesser time spent in the highly fuel efficient cruise phase of flight.
103
Flight Operations Support
10 September 2005
CFM PROPRIETARY INFORMATION
Subject to restrictions on the cover or first pa ge
Estimated Severity Reduction Due
to the Use of Reduced Takeoff Thrust
0 5 10 15 20 25
Estimated
Severity
Reduc tion -
%
Average Takeoff Reduced Thrus t - %
This chart represents the relative
impact of reduced thrust
increments on severity.
This shows that the first increment
of thrust reduction is the most
important but that thrust reduction
even at the higher increments is
important.
Severity Analysis
Reedduucceedd TTaakkeeOffff TThhrruusstt
　
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