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2.7.1. Influencing factors
Chapter B-Background introduced to the aircraft performance monitoring methods and reminded the possible causes for bias and/or scatter on the analysis.
The APM program has evolved over the past twenty years so as to account for automated correction calculations to take into account part of the influencing factors.
Amongst these, the Coriolis effect is taken into account. Entering the aircraft position and heading will make the influence calculated automatically.
An energy correction is included to the APM to take into account variations in kinetic (FPAC – acceleration / deceleration) and potential energy (IVV -inertial vertical velocity). The energy variations due to horizontal and/or vertical accelerations are taken into account through the values recorded in-flight (flight path acceleration, inertial vertical velocity). This reduces the scatter of the APM results but is only valid for small movements around the equilibrium point respecting the stabilization criteria. It boils down to remain in the linearized part of the equations of movement programmed into the APM.
Note: No FPAC / IVV, C.G. corrections taken into account in the A300B2 / B4 program.
The other corrections (such as loss/gain of performance due to isobar slope, …, etc, …) are not taken into account and as a result will introduce bias and/or scatter on the output result. The purpose of routine monitoring being to monitor the trend of the aircraft performance, the APM analysis does not require any further corrections as long as the same assumptions are kept for the analysis (especially the fuel Lower Heating Value).
Flight Operations & Line Assistance Getting to Grips with Aircraft Performance Monitoring
CRUISE PERFORMANCE ANALYSIS
2.7.2. Aircraft bleed configuration
The APM program can use DMU cruise performance report number 02 (CPR<02>) as an input file. One of the entries, which is required by the APM program, is the bleed flow for each pack. The cruise performance report 02 contains the pack bleed flows.
As far as the bleeds are concerned,
-No cruise performance report is produced whenever the configuration is not as
required: anti ice OFF, cross feed valve open, symmetrical valve positions -A given record is not analyzed whenever the recorded difference between pack
flow 1 and pack flow 2 is higher than 10%.
Focusing on the second item, the following is worth mentioning it.
The bleed flow asymmetry has an impact on the theoretical fuel flow (FFTH). The APM program must use the mean value of left and right bleed flows to iterate the FFTH. A 10%-margin was retained so as to avoid error in calculating the DSR greater than 0.1%. More precisely, when the data is read from a CPR<02>, the bleed flow is defined by pack left/right flows. The APM program cope with these two values by:
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averaging both values to get a single value,
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getting to grips with aircraft performance monitoring(50)
