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remain much closer to the optimum. In addition the high profile (depending on
the aircraft) remains much higher than the optimum, increasing the fuel penalty.
This profile is shown on the following page.
Step Climb Profiles
Odd Flight Levels Non RVSM
26000
28000
30000
32000
34000
36000
38000
40000
42000
0 1000 2000 3000 4000 5000 6000 7000 8000 9000
Distance from Brake Release - nm
Altitude - ft
Low Profile
Mid Profile
High Profile
Optimum Altitude
Maximum Altitude
Maximum Altitude Optimum
Altitude
Getting to grips with Fuel Economy IN FLIGHT PROCEDURES
- 43 -
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.
Step Climb Profiles
Odd Flight Levels RVSM
26000
28000
30000
32000
34000
36000
38000
40000
42000
0 1000 2000 3000 4000 5000 6000 7000 8000 9000
Distance from Brake Release - nm
Altitude - ft
Low Profile
Mid Profile
High Profile
Optimum Altitude
Maximum Altitude
Maximum Altitude Optimum
Altitude
5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy
- 44 -
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.
Getting to grips with Fuel Economy IN FLIGHT PROCEDURES
- 45 -
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
Thus delaying a climb to a higher altitude has a significant impact on fuel
burn.
5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy
- 46 -
5.3.2.4 OPTIMUM ALTITUDES ON SHORT STAGES
For short stages, the choice of cruise flight level is often restricted due to the
necessary climb and descent distance. Airbus philosophy assumes a minimum 5
minute cruise sector, because a climb followed immediately by the descent is not
appreciated by pilots, passengers or ATC.
If the stage length is of sufficient length that the optimum flight level can be
reached, but the cruise is of short duration, then the benefits at this flight level
will be marginal. It may even be worthwhile to cruise at one flight level lower, as
the increased climb consumption offsets any reduced cruise consumption.
In the FCOM there is a chart showing the optimum altitude on a short stage.
An example is shown below.
Getting to grips with Fuel Economy IN FLIGHT PROCEDURES
- 47 -
5.3.3 CRUISE SPEED OPTIMISATION
Having been given a flight level which may be a requested optimum altitude
or one imposed by air traffic control, speed is the only remaining parameter that
requires selection. The following picture shows the variation of Specific Range with
Mach Number for different aircraft weights at a fixed altitude.
The Mach number, which gives the best specific range, can be determined. It
is called the maximum range cruise Mach (MMR). Nevertheless, for practical
operations, a long-range cruise procedure is defined which gains a significant
increase in speed compared to MMR with only a 1% loss in specific range. Like the
　
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