HOW TO RECORD IN-FLIGHT PARAMETERS
3.3. Data analysis procedure
Based on in-flight recorded data, aircraft stability will be assessed from the ground speed. The most representative of a 6-minute run will be selected. One or more 6-minute shots will be retained if possible. Stability criteria given in the previous paragraph will also guide this choice.
The input data must be prepared for and analysis according to the following rules:
- Pressure altitude, Mach number, TAT, N1 (or EPR) and fuel flow will be averaged over the selected 6 minute-portion.
- Aircraft gross weight will be based on the difference between ramp weight at MES and fuel used at center point of the selected 6 minute-portion.
- The aircraft CG will be calculated from takeoff CG and fuel schedule (when not part of the recorded data)
- Aircraft acceleration along the flight path (FPAC) will be the slope (linear regression) of ground speed over the 3-minutes frames ; the same applies for the vertical speed but sloped through altitude.
FLHV, latitude, heading are introduced to take into account fuel calorific content and Coriolis / Centrifugal and local gravity effects respectively as discussed in chapter B.
The selection of 6 minute-portions from the recorded data enables to obtain a mean value, to evaluate scatter, which is indicative of measurement stability. Final assessment is only possible when taking into account correction factors, which, in turn, also allow to decrease bias and scatter. In particular, the application of the FPAC correction effectively reduces scatter. An uncorrected FPAC of 1kt/minute corresponds to a drag deviation of approximately 1.3%.
Then, for each 6-minute segment, one set of data is obtained. The analysis of the resulting points can be performed with an Airbus specific tool, based on the specific range method: the APM program.
Statistical elimination can be selected before the analysis in the APM program. For each parameter (fuel flow, N1/EPR,…), the mean value and the standard deviation is calculated over all the records. The user can filter these records so as to get rid of lesser quality readings. Two filters are implemented in the APM program: -standard elimination which discards the points which are outside a 95%-
confidence interval -pre-elimination window which allows the user to eliminate the parameters
which are outside a user’s defined window, which is centered around the mean
value.
Flight Operations & Line Assistance Getting to Grips with Aircraft Performance Monitoring
HOW TO RECORD IN-FLIGHT PARAMETERS
4. AUTOMATIC RECORDINGS
4.1. What is automatic recording?
Manual recording was introduced in paragraph 3. It is obvious that this way of collecting data cannot apply in case of routine aircraft performance monitoring.
At Airbus we have conceived a process, that minimizes handling operations. This process is based on the utilization of the aircraft recording systems for data collection. Automatic recording means configuring aircraft systems so as to get in-flight data automatically recorded for further analysis by the IFP or APM program.
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