Figure F2 - Comparison CFP versus FMS predictions
Apart from the routing errors, the figures in both cases are quite consistent with each other.
4. AIRBUS TOOLS AND FUEL FACTOR
All airline Flight Operations use or at least have heard about the Airbus High Speed Performance calculation software. The intent of this paragraph is to briefly explain how to use fuel factors with these tools.
The Airbus HSP software is composed of: -the IFP program
- the FLIP program -the APM program
Flight Operations & Line Assistance Getting to Grips with Aircraft Performance Monitoring
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USING THE MONITORED FUEL FACTOR
4.1. The IFP program
This paragraph describes the way to use fuel factors (monitored fuel factor, FMS PERF FACTOR) in the IFP program, depending on what is needed. For more details on the IFP functions, read 0-1.1.3. The IFP program.
4.1.1. The IFP calculation modes
The IFP has three basic calculation modes. They are described down below.
4.1.1.1. Standard mode Calculations performed with this mode are based on the most accurate physical model of the aircraft available (so-called the IFP model or book level), giving the most accurate fuel predictions for given speeds. Calculations are possible at economic speeds for the cruise phase only, by selecting the "optimum speed" option. But, the resulting calculations will not match up entirely with the speeds the aircraft will be adopt by means of the FMS and in equivalent conditions. These are
indeed based on the optimization of the cost function using slightly different data than those stored in the FMS.
This calculation mode is based on:
-Standard IFP aerodynamic and engine database (same as book level)
-Standard IFP algorithms for data extraction and flight mechanics equations
-Standard data and algorithms for flight guidance parameters and limitations
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Adjustable atmospheric conditions
-All air conditioning settings available
-All anti ice settings available
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Adjustable FLHV
-Adjustable drag factor (modification of the aircraft drag)
-Adjustable fuel consumption factor (modification of the fuel flow)
4.1.1.2. FMS mode Calculations performed with this mode are based on the databases stored in the FMS (FMS Perf Data Base or PDB) on the simplified equations used therein (due to the real-time constraints). For a given cost index and fuel factor, speeds given in this mode are thus the same as those flown by the aircraft in the same conditions. Fuel consumption may be slightly different from the ones actually observed, since there are some simplifications, like the assumption of low air conditioning and no anti ice whatever the actual bleed flow (see conditions below). Another restriction
is that only flight conditions that can be flown under FMS managed mode are available for computation.
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