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CFP based on Greendot or a mix of LRC/MRC

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CFP based on Greendot or a mix of LRC/MRC

Old 3rd Mar 2009, 03:45
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CFP based on Greendot or a mix of LRC/MRC

Just clarifying that I support the latter , but some people are under the impression that airline CFPs in the case of A330 202 are based on green dot speed rather than LRC/MRC

Any inputs appreciated
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Old 3rd Mar 2009, 05:04
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I'm not Airbus rated, but it's my assumption that the Green Dot equates to Best Angle of Climb / Minimum Manoeuvre Speed / Best Holding Speed / Engine Inoperative Drift-Down Speed, all of which are fairly much the same with only minor differences to Vmd. If my assumption is incorrect, please do not read further.

Be assured that Flight Planning will be based upon Cost Index (CI), which nowadays lies somewhere between Max Range Cruise and Long Range Cruise.

Cruise at your best Holding speed (if my Green Dot assumption is correct) would be disastrous from a Flight Planning point of view. VERY high altitude cruise COULD result in Green Dot being close to CI speed, this would be the exception.

I'll delete this post if my Green Dot assumptions are incorrect, promise.


Old Smokey
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Old 3rd Mar 2009, 09:21
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Old Smokey, your Green Dot assumptions are correct.

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Old 3rd Mar 2009, 12:17
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Strange as it may sound, CRUISE AT GREEN DOT SPEED is an option available on the Airbus, so YOUR cruise speed displayed on the CFP will depend on what your airline decided to use!

Other options are:
  • Cruise at given K*Vs
  • Cruise at given Mach or CAS
  • Cruise at optimum speed
  • Cruise at maximum speed
  • Cruise at optimum altitude and given speed
  • Cruise at optimum altitude and optimum speed
  • Cruise at green dot speed
  • Cruise at optimum and green dot speed

So its up to the airline to decide which they want to use.

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Old 3rd Mar 2009, 13:31
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Simple question, complex answers. It depends on the sophistication of your Flight Planning System, the airline operator parameters and restrictions used, and the operators planning priorities for fuel and time.

The most efficient is to use Cost Index, based on a City Pair generated cost index.

The speed on the CFP will be a function of the CI, weight, environmental conditions, airspace restrictions (fixed mach areas) and minimum/maximum speed schedules.

With the use of CI the speed can vary from MRC to just below VMO/MMO, far above LRC, which in simple terms is 1% SFC reduction from MRC.

On the Airbus products it is possible when using CI=0 or low CI values that the speed will be very close to Green Dot or when operating at the top end of the altitude/weight/temp envelope.

I have had a chance to view a lot of different Flight Planning Systems and CFP's and have not seen what yet that was planned based on Green Dot for the Airbus products.
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