NR 11 12 11 12 12 11 1112 11 11 11    12 11

 *  VALUES OUT OF RANGE (MARKED BY A TRAILING "*") ARE NOT INCLUDED IN MEAN VALUES (MV) AND STANDARD DEVIATIONS (SD).
 SO NUMBER OF CASES MAY BE REDUCED TO NUMBER OF READINGS (NR). ".---" MEANS FAILED OR NOT CALCULATED.

Figure B20: Trending with the APM program
Figure B20 analysis shows that this particular tail number consumes more fuel than the IFP book level by 1.228% (worse specific range by 1.228%) in average. Based on the sample in-flight records that were snapshot during the flight, the deviation to this mean value was ±0.65%. Eleven records were used to calculate the statistics.
More details concerning data interpretation is available in Chapter D-Cruise Performance Analysis.

3.5. Conclusion
3.5.1. Trends and factoring
Routine aircraft performance monitoring is double-purpose. First, it enables to
establish the different fuel factors for aircraft operations for each individual aircraft.
Second, it allows to monitor the natural performance deterioration trend with time.

Trends can provide essential information concerning the impact of a maintenance
policy provided adequate book-keeping is performed to record:
-numeric APM outputs before and after maintenance actions,
-strategic maintenance actions (airframe, engines, instruments).
Deteriorating from delivery, each individual aircraft specific range trends compared
to the Airbus baseline provide the performance factor that is eventually entered
into that aircraft’s FMS and in the flight planning system for fuel padding.

Flight Operations & Line Assistance Getting to Grips with Aircraft Performance Monitoring

BACKGROUND
To illustrate the trend of the aircraft performance deterioration with time, and
based on the feedback from A320 family customers, the following typical in-service
performance values in terms of specific range versus the corresponding IFP level
are as follows:
-after 1 year from delivery: 2.0% below IFP +/- 1%
-after 2 years from delivery: 3.5% below IFP +/- 1%
-after 3 years from delivery: 4.0% below IFP +/- 1%

3.5.2. Comparing performance monitoring methods
Moreover, when checking the actual performance level of an aircraft, many factors may influence the analysis by introducing bias and/or scatter. Although corrections may be calculated for each individual factor, this procedure appears to be quite hard when routine performed.
Overall, three basic methods are available to check the actual performance level .SR
of the aircraft versus the book level: the specific range method ( ), the fuel
SR .FU .FBO
used method ( ), the fuel on board method ( ). Depending on the
FU FBO method used, part or all of the influencing factors are taken into account. Each method gives an apparent performance level of the aircraft, which is the combination of the actual aircraft performance level and of the influencing factors.
　
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