HOW TO RECORD IN-FLIGHT PARAMETERS
An aircraft quality number characterizes each report. It is defined thanks to the below formula:
VAR(N )QA =∑W (N ) × TOL(N )2
where N is parameter number N (can be the N1, fuel flow…)
W(N) is a weighing factor (between 0 and 1)
VAR(N) is the individual variance
TOL(N) is the individual variation value
The lower the quality numbers the better the stable frame report. QA varies
between 0 and 999. Common values seen in routine monitoring are around 40.
The quality numbers are not used as a trigger condition but are used to detect the
best report during a searching period.
The operators can use it so as to eliminate possible irrelevant recordings. Most of
the time, quality numbers are not used because it is hard to get some points,
especially for short-range flights.

Example of trigger logic and conditions for an A320 aircraft fitted with IAE engines
The DMU/FDIMU generates the CPR<02> based on flight hours or flight legs. The
choice is programmable via the GSE.
Depending on the basis for searching, the DMU/FDIMU searches in cruise phase
for report generation with stable frame criteria where the best aircraft quality
number is calculated. The report with the best quality number is then stored in the
report buffer.

The basic DMU/FDIMU configuration for the A320 aircraft is:
1.
Searching time frame: 1 hour

2.
Observed data during five sub-periods of 20 seconds each. The best period is retained thanks to the quality number.

3.
The stability criteria, which must be met are:

Parameter  Limit 
Inertial Altitude  150 feet 
Ground Speed  6 kt 
Roll Angle  0.8 degrees 
TAT  1.1 degrees C 
N2  0.9 % 
EGT  18 degrees C 
Vertical Acceleration  0.03 g 
Mach Number  0.008 Mach 
N1  1.6 % 
P2  0.05 psia 
Fuel Flow  100 kg/h 
EPR  0.035 

Flight Operations & Line Assistance Getting to Grips with Aircraft Performance Monitoring
HOW TO RECORD IN-FLIGHT PARAMETERS

4.5. Data analysis procedure
The analysis procedure is much simpler compared to the case when performing manual recordings because the stability criteria were already checked by the DMU/FDIMU before parameters are recorded. As of a consequence, no further assessment of the parameter stability is required.
All the input data were stored in the Cruise Performance Report <02> apart from a few parameters that are given down below:
-The fuel Lower Heating Value: as this value cannot be read in the report, it must be obtained from another source. When performing an audit, a fuel sample will be analyzed and the corresponding FLHV will be identified. In case of routine performance monitoring, the FLHV will be assumed equal to a standard value. Most commonly, the value 18590 BTU/LB is used for analysis. Yet some precautions have to be taken, in order not to bias the calculated different fuel factors (see Chapter F-Using monitored fuel factor).
　
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