Thus pilots are advised to perform step climbs around the optimum altitudes. To facilitate this, the optimum weight for climb to the next flight level is given in most FCOM’s (not A300/A310). An example is shown below.
 
 

 
On all Airbus FMS-equipped aircraft, the optimum altitude (OPT FL) and 
the maximum flight level (MAX FL) are displayed on the MCDU progress page. The recommended maximum altitude in the FMGC ensures a 0.3g buffet margin, a minimum rate of climb of 300ft/min at MAX CLIMB thrust and a level flight at MAX CRUISE thrust. Depending on weight and type, it is 2000 to 4000ft above the optimum altitude.
 
Typical cruise distances between 2000 foot altitude steps are shown in the following table:
Type
 Distance - nm
 
A300
 1000 - 1100
 
A310
 1150 - 1250
 
A320
 1200 - 1300
 
A330
 1500 - 1650
 
A340
 1500 - 1650
 
A340-500/600
 1600 - 1700
 

 
For sector lengths greater than these, where ATC restrictions do not allow a change in cruise altitude from the initial requested level, the initial request should be the highest compatible with the maximum cruise altitude.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
5.3.2.3 DELAYS IN ALTITUDE CHANGES

 
Let’s consider an aircraft that is at flight level 330, which has, at that weight, an optimum flight level of 370. If it does not climb to FL 370 for ATC or other reasons, it will consume more fuel. The following table shows the difference in fuel burn for a 500nm still air cruise, when cruising at FL 330 instead of FL 370.
 
Aircraft
Type
 Fuel Increase
(kg)
 Fuel Increase
(%)
 
A300B4-605R
 238
 5.2
 
A310-324
 221
 5.3
 
A318-111
 150
 6.2
 
A319-132
 184
 7.9
 
A320-211
 158
 6.2
 
A320-232
 187
 7.9
 
A321-112
 155
 5.5
 
A330-203
 324
 5.5
 
A330-343
 342
 5.6
 
A340-212
 393
 6.2
 
A340-313E
 378
 6.0
 
A340-500/600
 336
 4.1
 
　
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