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Aircraft Type A.P.U. type
Engine FF
kg/hr/eng
APU FF
kg/hr
Extra Fuel for
1 minute
A300 GE 331-250 520 150kg 6kg
A310 GE 331-250 520 150kg 6kg
A320 family CFM 36-300 300 105kg 3kg
A330 GE 331-350 520 175kg 6kg
A330 RR 331-350 720 175kg 9kg
A340 CFM 331-350 300 175kg 2kg
A340 RR 331-600 480 275kg 4kg
In overall economic terms, the benefits of APU operation are not just
confined to fuel usage. The hourly maintenance costs of an APU are cheaper than
the aircraft powerplant, so reducing ground running time on the engines can
significantly reduce the operating costs.
Getting to grips with Fuel Economy 4 - PRE-FLIGHT PROCEDURES
- 23 -
4.7 AERODYNAMIC DETERIORATION
Some of the most severe penalties in terms of fuel consumption are caused by
increased drag resulting from poor airframe condition. Normal aerodynamic
deterioration of an aircraft over a period of time can include the incomplete
retraction of moving surfaces, damaged seals on control surfaces, skin roughness
and deformation due to bird strikes or damage caused by ground vehicles,
chipped paint, mismatched doors and excessive gaps. Each deterioration incurs a
drag increase, and this increased drag is accompanied by increased fuel
consumption.
This subject is covered fully in the brochure “Getting Hands-On Experience with
Aerodynamic Deterioration”.
The following table gives the highest deterioration effect in each category for the
three aircraft families as increased sector fuel consumption in Kg, based on typical
utilization figures.
Category Condition A300/310 A320
Family
A330/340
Misrigging Slat 15mm 90 60 270
Absence of Seals Flap (chordwise) 30 14 90
Missing Part
(CDL)
Access Door 50 13 150
Mismatched
Surface
Fwd Cargo Door
10mm step for
1m
20 11 80
Door seal leakage Fwd Pax Door
5cm
2 1 5
Skin Roughness 1 m2 21 13 105
Skin Dents Single 2 1 2
Butt joint gaps Unfilled 0.2 0.1 0.6
Butt Joint Gaps Overfilled 3 2 7
External Patches 1 m2 3mm high 6 3 16
Paint Peeling 1 m2 leading
edge slat
12 8 57
Sector Distance 2000nm 1000nm 4000/6000nm
5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy
- 24 -
5. IN FLIGHT PROCEDURES
When an aircraft arrives at the end of the runway for take-off, it is the
flying techniques (speed, altitude, configuration, etc) that have the biggest
influence on fuel economy. Disciplined flight crews adhering to a flight plan based
on the operator’s priorities can save much fuel and/or costs.
This part intends to give recommendations to flight crews on the means to
save fuel during the flight. It reviews the different phases of the flight, that is to
say:
• Take-off and Initial Climb
• Climb
• Cruise
• Descent
• Holding
• Approach
Getting to grips with Fuel Economy IN FLIGHT PROCEDURES
- 25 -
5.1 TAKE-OFF AND INITIAL CLIMB
5.1.1 INTRODUCTION
There are many variations in take-off technique that can directly affect the
fuel burn. In general the effects are very dependent on the airframe/engine
combination as well as aircraft weight, airfield altitude and temperature. The
following fuel effects are representative values.
5.1.2 BLEEDS
For take-off, full bleeds can be used or one can consider selecting packs off
or APU bleed on to improve take-off performance. Selecting packs off without
APU will also improve fuel burn. The normal procedure would then be to select
pack 1 on after climb thrust is selected and pack 2 on after flap retraction. This
has the effect of reducing fuel burn by 2-3 kg on an A320 increasing to 5-10 kg
on an A340-500/600.
With APU bleed the engine fuel burn will be decreased by the same amount.
However with APU used from pushback with 12minutes taxi, the additional APU
fuel burn is 30kg for an A320 and 60-70kg for an A340.
In economic terms, the APU fuel and maintenance cost is largely offset due
to decreased engine maintenance costs bleeds off (higher flex temp).
5.1.3 CONFIGURATION
This effect is very dependent on the variables mentioned in the introduction,
plus the choice of VR and V2. However the trend is always the same , with high
flap/slat configurations (more extended) using more fuel than the lowest setting.
Typical penalties/takeoff of higher flap settings compared with the low flap
settings Conf 1+F are shown below (note that for the A300/A310 Conf 1+F, Conf
2 and Conf 3 corresponds to the Flap 0,15 and 20 configuration respectively).
Aircraft Conf 2 Conf 3
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