3.2.3.3. FLIGHT PLAN ACCURACY
In terms of aircraft operation, an accurate, Computerized Flight Plan (CFP) is one of the most important means of reducing fuel burn.
As is the case with most computer systems, the accuracy of the data provided to a CFP system will influence the accuracy of the CFPs it produces. However, the nature of some of the parameters can bring a certain degree of inaccuracy. For example:
.
Weather conditions: particularly temperatures and wind strengths/directions.
.
Fuel specification (lower heating value): defines the heat capacity of the fuel standard fuel. Engine thrust depends on the amount of heat energy coming from the fuel it is burning. The aircraft database may contain a standard or average value that may not correspond to the actual fuel used. A fuel analysis or data from the fuel provider can provide the necessary clarification.
. Inclusion of actual ATC constraints.
. Up-to-date aircraft weight: aircraft weighing is a scheduled maintenance action and
the latest data should be systematically transferred to the CFP system.
. Payload estimation: assessment of passenger baggage and cargo variations with route
and season.
. Aircraft performance degradation: refer to following section.
. Fuel reserves: refer to section below.
3.2.3.4. AIRCRAFT PERFORMANCE DEGRADATION
With time the airframe and engine deteriorate and the aircraft requires more fuel for a given mission. These deteriorations can be partially or fully recovered through scheduled maintenance actions. Deterioration will begin from the moment the aircraft enters service and the rate will be influenced by the utilization and operation of the aircraft.
The Aircraft Performance Monitoring (APM) module of the Airbus Performance Engineering Program (PEP) software package (see text box on page 13 for more information) allows aircraft degradation with time to be calculated. It can also be used as a means of triggering maintenance actions to recover some of the degradation.
The implementation of an Aircraft Performance Monitoring program requires the processing of data through the APM software. The required data, known as “cruise points”, are automatically recorded by the aircraft. Depending on the aircraft’s configuration the transfer of these data can be achieved via either printouts from the cockpit printer, a PCMCIA card or diskette, or via the ACARS system.
The performance degradation for each individual aircraft is an important parameter. Accurate interpretation of this factor will enable the fuel usage predictions of the Flight Management System (FMS) to better match those of the CFP system.
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