2.7.4. Recommended Maximum altitude (REC MAX ALT)
The FMS RECommended MAXimum ALTitude (REC MAX ALT) is defined as the
altitude, which can be:
-flown with a speed higher than GREEN DOT and lower than VMO/MMO,
-reached with a minimum vertical speed of 300ft/mn at Max climb thrust,
Flight Operations & Line Assistance Getting to Grips with Aircraft Performance Monitoring
USING THE MONITORED FUEL FACTOR
-flown in level flight without acceleration with an engine rating less than Max cruise,
-reached before buffeting (the margin depends on the aircraft models, 0.3g for fly-by-wire aircraft)
It is displayed on the MCDU PROG page.
The REC MAX ALT is less than or equal to the CERtified MAXimum ALTitude as provided in the Airplane Flight Manual (AFM). This calculation is permanently updated during flight.
The REC MAX ALT is a pre-computed value function of the aircraft gross weight and the ISA deviation (the ISA model is defined in the FMGEC thanks to the temperature and the tropopause altitude that are entered in the MCDU).
As a consequence, the PERF FACTOR has no influence on the REC MAX ALT.
2.7.5. Optimum altitude (OPT ALT)
The Optimum Altitude function is defined as the altitude at which the cost, - and at the optimum speed, -at its minimum. This calculation is permanently updated during flight.
Flight Operations & Line Assistance Getting to Grips with Aircraft Performance Monitoring
USING THE MONITORED FUEL FACTOR
It is displayed on the MCDU PROG page.
The calculation is made taking into account: the Cost Index, the aircraft gross weight (GW), the wind model, the temperature model (International Standard Atmosphere) and the ISA deviation.
Since the PERF FACTOR modifies the fuel flow, it changes the cost function. As a consequence, the OPT ALT is also impacted.
A positive PERF FACTOR decreases the OPT ALT, all other conditions being fixed.
3. FUEL FACTOR FOR FLIGHT PLANNING SYSTEMS
During the dispatch of any aircraft, each operator must determine the fuel quantity that is required for a safe trip along the scheduled route, and reserves to cover deviations from the planned route according to locally prevailing regulations.
Each operator has his own fuel policy and tools to prepare the required flight planning. Some operators have built in-house programs. Some others subcontract this to third party specialized in that area.
No matter which the option is chosen by the operator, all flight planning is basically based on: -the Airbus aircraft High Speed Performance databases (IFP databases, FMS
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