3.
the monitored fuel factor is equal to 2%
Assuming no Cost Index calculation is done, the flight planning fuel factor is
equal to the monitored fuel factor corrected for the FLHV effect, that is to say:
.. 18400 .
2.0% ..1 .×100 ≈ 0.98% ≈ 1.0%
. 18590 .
4. The FMS PERF FACTOR should be indicated on the computerized flight plan so that pilots can check the computerized flight planning and FMS predictions are consistent with each other. Of course, the FMS PERF FACTOR can be different from the flight planning fuel factor determined above. But the pilots only have at hand the fuel factor that is defined for the FMS predictions, that is to say, the FMS PERF FACTOR.
Flight Operations & Line Assistance Getting to Grips with Aircraft Performance Monitoring
USING THE MONITORED FUEL FACTOR
3.3. Comparing FMS fuel predictions and Computerized FlightPlanning
FMS fuel predictions and scheduled fuel planning indeed have different purposes. Yet, it is tempting to try to compare both fuel schedules. The intent of the following is to remind the main reasons for these differences.
As explained in this chapter, the FMS predictions are based on an FMS simplified performance database, which is different from the CFP aircraft database (consistent with the book level).
1.
The fuel factors defined in the FMS (PERF FACTOR) and those destinated for flight planning computation (flight planning fuel factor) must be consistent with each other.
2.
The FMS predictions may be calculated with different wind predictions than the Computerized Flight Planning (wind profile). The influence of the wind on performance is tantamont.
3.
The flight planning computation method can induce hidden effects:
.
Some flight plannings are based on Flight Crew Operating Manual pre-calculated data. The flight plan is then calculated interpolating within FCOM data.
.
Some flight planning systems are based on pre-calculated data using the Airbus IFP program. The flight plan is then calculated interpolating within resulting data tables
.
Some other flight planning systems are based on real-condition computation, which is the most accurate method, avoiding interpolation errors
4.
The ECON speeds may be determined based on an algorithm, which is not exactly consistent with the Airbus one. As of a consequence, a slight difference between scheduled ECON speeds and observed ECON speeds may occur.
5. The FMS predictions are updated in real-time, based on the actual flight profile. The Computerized Flight Planning is established at dispatch and does not include any correction for deviations from planned conditions.
Flight Operations & Line Assistance Getting to Grips with Aircraft Performance Monitoring
USING THE MONITORED FUEL FACTOR
Example of difference between CFP and FMS predictions Figure F2 shows an example of predictions, for the same route, all above specified conditions being fulfilled.
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