BACKGROUND

Figure B18: Stable frame = PMAX-PMIN < DP limit for all parameters
The FDIMU/DMU collects most of the data. The data comes from the various aircraft systems (such as the ADIRS, the FAC…). Potential accuracy tolerance remains in the normal industrial tolerances for each of these systems.
Some of the data is measured by the systems, and therefore can suffer from measurement error. Some other data (such as the flight path acceleration parameter, which quantifies the change of aircraft speed along the flight path) are calculated by means of the FDIMU/DMU based on an average of several other parameters. As a consequence, a rounding error comes on top of the measurement and tolerance errors.
Yet, the total error on the overall data collection remains quite low when compared to the other potential sources of errors described in this chapter.
On the data transmission side (either via ACARS, or dumping on a PCMCIA or disk), the only errors possible are due to a FDIMU/DMU malfunction.
Flight Operations & Line Assistance Getting to Grips with Aircraft Performance Monitoring

BACKGROUND

3.4.4. Taking into account influence factors
When doing an aircraft performance audit, it is important to deal with all these bias / scatter effects in the best way possible. The following measurement considerations/corrections factors are essential:
Introducing bias  Introducing scatter 
Fuel LHV  data acquisition/transmission 
Aircraft weight  instrument scatter 
air conditioning / bleed selection options  Auto-throttle / autopilot activity 
aircraft trimming  atmospheric influences 
instrument accuracy  stabilizer / elevator / trim 

When doing routine aircraft performance monitoring, it is difficult to try assessing the impact of the previously mentioned factors. Indeed, taking a fuel sample to the laboratory for each flight is really not feasible. Hence, some assumptions must be made, leading to introduce some uncertainty on the cruise performance analysis. Routine aircraft performance monitoring is based on a statistical approach, which gives an average deterioration and the associated scatter.

Figure B19: Performance monitoring trends
Identifying trends is rather the goal of routine performance monitoring. Figure B20 illustrates the type of trending that can be performed with the APM program.
Flight Operations & Line Assistance Getting to Grips with Aircraft Performance Monitoring

BACKGROUND
* A I R B U S C R U I S E  P E R F O R M A N C E  * A I R C R A F T PERFORMANCE MONITORING *
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