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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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