2.
The fuel on board method,
3.
The specific range method.
This chapter is focused on the specific range method. For further details about the
two other methods, read Chapter H - Appendices.
This subject was already presented during the 7th Performance and Operations
Conference held at Cancun, Mexico in year 1992. This brochure is based upon the
leading article “Auditing aircraft cruise performance in airline revenue service”
presented by Mr. J.J. SPEYER, which was used as reference material.
This article is appended at the end of this brochure, see Chapter 0 - Appendix 6 -Auditing aircraft cruise performance in airline revenue service.
Flight Operations & Line Assistance Getting to Grips with Aircraft Performance Monitoring
BACKGROUND
3.1. The fuel used method
The basis of the fuel used method is to measure aircraft fuel burnt in level flight and over a significantly long time leg and to compare it to the fuel prediction of the Flight Crew Operating Manual (FCOM, Flight Planning sections) or of the High Speed Performance calculation program developed by Airbus (the IFP program).
This method probably provides less information than the specific range method but is also less constraining in terms of stability and data acquisition requirements. The method is also less accurate because of the lack of stability checks on the observed data.
3.2. The fuel burn off method
The trip fuel burn analysis compares genuine aircraft performance data for a whole flight with the forecasted computerized flight planning. Actual aircraft performance should be corrected depending on the differences between the actual flight profile and the predicted one.
3.3. The specific range method
3.3.1. Introduction
The data observed in flight represents punctual (instantaneous) airframe/engine performance capability. It is used to generate a measured Specific Range, which represents the actual aircraft fuel mileage capability (NM/kg or lb of fuel). The specific range represents the aircraft/engine performance level under stabilized conditions and thus constitutes the main reference criterion. It may not be representative of the actual fuel consumption of the aircraft during a whole flight.
3.3.2. Definition
The specific range (SR) is the distance covered per fuel burn unit. Basically, the specific range is equal to:
ground speed (GS)
SR (Ground) =
fuel consumption per hour (FF)
Considering air distance, the specific range is equal to:
true air speed (TAS)
SR (Air) =
fuel consumption per hour (FF)
As TAS is expressed in nautical miles per hour (NM/h), and Fuel Flow (FF) in kilograms per hour (kg/h), the SR is expressed in NM/kg or NM/ton.
Flight Operations & Line Assistance Getting to Grips with Aircraft Performance Monitoring
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