getting to grips with fuel economy(29)

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 For instance, for the A319, increasing the cost index from 0 to 20 reduces the block time by 15 minutes (5%) for a fuel burn increase of only 200kg (2%) on a 2000nm sector.
 
 
 
 
 
 
 
 
5.3.6  EFFECT OF SPEED INCREASE ON MANAGED MODE

 
Flying at a given cost index rather than at a given Mach number provides the added advantage of always benefiting from the optimum Mach number as a function of aircraft gross weight, flight level and head/tailwind components.
This means the ECON mode (“managed” mode) can save fuel relative to fixed Mach schedules (“selected” mode) and for an equivalent time.
One can wonder whether selecting a higher Mach number than the one chosen by the FMS has a significant impact on fuel consumption. Imagine an aircraft flying at flight level 370, in managed mode and at the optimum weight of FL370. The FMS computes the optimum speed based on cost index, temperature and wind. If the pilot selects another (higher) Mach number, the fuel consumption will increase. 
The following tables show the effect of such a speed increase. 
 
 
 
 Economic Mach No + 0.005
 Economic Mach No + 0.01
 
 
 
 
 Fuel Penalty
 .Time 
 Fuel Penalty
 .Time 
 
 
 Aircraft
 Sector
 Kg
 %
 Min
 Kg
 %
 Min
 
 
 A300-605 
 2000 Nm
 110
 0.4
 1
 230
 0.9
 3
 
 
 A310-324 
 2000 Nm
 90
 0.4
 1
 430
 2.0
 8
 
 
 A318 
 1000 Nm
 30
 0.5
 1
 60
 1.0
 1
 
 
 A319
 1000 Nm
 20
 0.2
 1
 40
 0.6
 2
 
 
 A320 
 1000 Nm
 20
 0.3
 1
 40
 0.7
 2
 
 
 A321
 1000 Nm
 10
 0.1
 1
 30
 0.4
 1
 
 
 A330 
 4000 Nm
 150
 0.3
 3
 330
 0.6
 6
 
 
 A340-212
 6000 Nm
 390
 0.5
　
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