2. A TOOL FOR ROUTINE ANALYSIS : THE APM PROGRAM
2.1. Introduction
The Airbus Aircraft Performance Monitoring program (APM) is devoted to high-speed performance analysis of all Airbus aircraft. It is useful a software anytime performance analysis is required. Indeed, the APM program enables to compare the aircraft cruise performance level (fuel consumption, engine parameters, specific range) as recorded during flight to book value performance data as stored in the aircraft’s high speed performance databases.
Flight Operations & Line Assistance Getting to Grips with Aircraft Performance Monitoring
CRUISE PERFORMANCE ANALYSIS
It calculates the deviation of flight parameters such as fuel flow, and N1/EPR
engine parameters from nominal book values. The end result is a delta specific
range, which reflects how far the aircraft is from its book value.
The specific range can of course be worse but also better than the book level
because this book level only represents an average performance level over a
number of brand new aircraft/engine combinations.
The delta specific range is the monitored fuel factor (opposite sign), which will
allow the operator to tune:
-the aircraft FMS flight plan on board the aircraft,
-the computerized flight planning and every high-speed performance related
studies in maintenance servicing, engineering or dispatch of the aircraft.
2.2. Basics
The APM calculates aircraft cruise performance in a so-called deterministic way. That is with the use of mathematical methods from the fields of probability, optimal estimation or filtering techniques and by using familiar equations of lift, drag and engine thrust in stabilized conditions during cruise. The analysis is called the Specific Range method. For each flight case, in flight recorded data is used to calculate a measured Specific Range (SR, distance covered per unit of fuel burnt). Results are then compared to the SR that is predicted for the given flight conditions (weight, altitude, TAT, Mach) based on a theoretical model. Following which, the program determines a deviation in specific range. Furthermore, it also enables a distinction between airframe and engine influence. By comparing book and measured values of engine power setting, fuel flow and exhaust gas temperature, a set of deviation parameters is being calculated to be produced in a result file.
The APM program schematically works as described in the following diagram. Orange boxes represent the theoretical model, blue boxes represent actual data.
Aircraft Global Performance degradation
Figure D1 – Schematic APM process (FF stands for Fuel Flow)
Flight Operations & Line Assistance Getting to Grips with Aircraft Performance Monitoring
CRUISE PERFORMANCE ANALYSIS
The input file contains information about Mach number, altitude, TAT, aircraft gross weight, CG location, bleed flow, FPAC (Flight Path Acceleration), IVV (Inertial Vertical Velocity).
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