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Subject to restrictions on the cover or first pa ge
TORA/TODA/ASDA
MTOW
TOGA
D04
D08
D12
D16
D20
D24
MTOW with Derated takeoff
Given runway length
MTOW for TOGA takeoff
MTOW for D12 (Derated takeoff)
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94
Flight Operations Support
10 September 2005
CFM PROPRIETARY INFORMATION
Subject to restrictions on the cover or first pa ge
Reduced thrust takeoffs restrictions
• On contaminated runways
- “More than 25 % of the required field length, within the width being used,
is covered by standing water or slush more than .125 inch deep or has
an accumulation of snow or ice.”
• If anti-skid system is inoperative
• These restrictions do not apply to “derated” takeoffs
• Any other restrictions on reduced thrust or derated thrust are imposed by the
aircraft manufacturer or operator; not by AC 25-13
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Flight Operations Support
10 September 2005
CFM PROPRIETARY INFORMATION
Subject to restrictions on the cover or first pa ge
Typical Additional Restriction applied by individual operators on Reduced
Thrust Takeoffs
Possible windshear
Brakes deactivated
Other MMEL items inoperative
De-icing performed
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AC 25-13 Restrictions
A periodic takeoff demonstration must be conducted using full takeoff thrust. An
approved maintenance procedure or engine condition monitoring program may
be used to extend the time interval between takeoff demonstrations
Anti-ice used for takeoff
Takeoff with tailwind
Wet runway
Performance demo “required”
96
Flight Operations Support
10 September 2005
CFM PROPRIETARY INFORMATION
Subject to restrictions on the cover or first pa ge
Operator methods vary e.g.
• Every tenth takeoff
• Every Friday
• Never make dedicated full thrust T/O for performance verification
- Take credit for ECM and full thrust T/O’s performed for operational reasons
Less reduced thrust benefits acrue when unnecessary full thrust takeoffs are performed
Full thrust takeoffs meaningful only when takeoff is performed at the flat rate temperature; otherwise the
takeoff data must be extrapolated to flat rate temperature
• Reduced thrust takeoffs can be extrapolated as well
• Cruise ECM data can also be used to predict EGT margin
Negotiate with regulatory agency to extend interval between dedicated performance verification
takeoffs
• Take credit for ECM programs (T/O or Cruise)
• Take credit for full thrust takeoffs performed for operational requirements
• Extrapolate data obtained during reduced thrust as well as full thrust takeoffs
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Periodic Takeoff Demonstrations
97
Flight Operations Support
10 September 2005
CFM PROPRIETARY INFORMATION
Subject to restrictions on the cover or first pa ge
- Max Thrust is not any more necessary!
Benefits of Reduced Thrust/Derated
- Lower Takeoff EGT
- Fewer operational events due to high EGT
- Lower fuel burn over on-wing life of engine
- Lower maintenance costs
EGTMargin decrease slowly SFC kept at low rate
Better Engine performance retention - Longer engine life on wing
- Shop Visit rate decrease
- Improved flight safety
For a given TakeOff, engine stress decreasing,
probability of engine failure decrease on that TakeOff.
TakeOff thrust is reduced when REAL GW < MAX LIMITING GW
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98
Flight Operations Support
10 September 2005
CFM PROPRIETARY INFORMATION
Subject to restrictions on the cover or first pa ge
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Three engine parameters that determine the degree of engine severity are rotor
speeds, internal temperature and internal pressure. Operating an engine at a
lower thrust rating or at reduced thrust reduces the magnitude of these parameters,
thus reducing engine severity.
Less severe operation tends to lower EGT deterioration. Since lack of EGT
margin is one cause of scheduled engine removals, lowering the EGT deterioration
rate can increase the time on wing between shop visits.
Fuel flow deterioration rate varies directly with EGT deterioration rate, thus
decreasing with the use of reduced thrust.
Maintenance costs are reduced because of the longer time between shop
visits and the lower labor and material costs of the shop visit to restore the
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CFFM556 Flight Operations Support(13)
