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options.
Aircraft 250KIAS at FL100 LRC at FL100
ΔFuel – kg ΔTime – min ΔFuel – kg ΔTime – min
A300-600 70 1.1 95 0.4
A310 70 1.1 90 0.3
A320 family 50 1.1 65 0.2
A330 80 1.2 100 0.5
A340-200/300 95 1.2 105 0.5
A340-500/600 135 1.2 125 0.5
Cruising faster at 10000ft reduces the time penalty at the expense of fuel.
After a long flight with an A340–500 or –600, starting the descent some
100nm early would not appear to be significant in the overall flight. However this
can result in a 900kg fuel burn increase and 8 minutes longer block time.
5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy
- 62 -
5.5 HOLDING
5.5.1 INTRODUCTION
When holding is required, it is generally flown on a “race track pattern”,
composed of two straight legs plus two 180 degree turns. In a hold the distance
covered is not the primary objective. On the contrary, the knowledge of the
maximum holding time (maximum endurance) is a determining factor for any
diversion decision. As a result, it is important, during holding, to try to minimize
fuel by simply minimizing fuel flow.
For all aircraft, the minimum fuel consumption speed is very close
to the maximum lift-to-drag ratio (Green Dot) speed as shown below. As a result,
in clean configuration, the standard holding speed is selected equal to green dot
speed (GD).
Fuel Consumption
A330-343 170000kg 1500ft
0
2000
4000
6000
8000
160 180 200 220 240 260 280 300 320
Speed - Knots CAS
Fuel Consumption kg/hr
GD
Min Fuel Min Drag Max Range Long Range
Holding patterns may be quite limiting around certain airports due to
obstacle proximity. Therefore, green dot is sometimes too high, especially during
turn phases where the bank angle can be too significant. As it is not possible to
significantly reduce the speed below green dot in clean configuration, slats may
be extended and a holding done in CONF1 at “S” speed. (min slat retraction
speed Conf 1 to Conf clean).
At other airports, Air Traffic Control may require the hold to be performed at a
certain speed, and it may not be possible fully optimise the fuel burn. In order to
Getting to grips with Fuel Economy IN FLIGHT PROCEDURES
- 63 -
allow flexibility in planning and operations, the FCOM has four different holding
speed and configuration combinations, adapted to each type of aircraft.
The following table gives the configurations and speeds for each type.
Aircraft types
First Flap/slat
Configuration Clean configuration
A300-600 210kts S speed 240kts Green Dot
A310 170kts S speed 210kts Green Dot
A320 Family (CFM) 170kts S speed 210kts Green Dot
A320 Family (IAE) 170kts S speed 210kts
Green Dot +
20
A330 170kts S speed 210kts Green Dot
A340-200/300 210kts S speed 240kts Green Dot
A340-500/600 240kts S speed - Green Dot
For the A300/A310 the first configuration is flap 15, slat 0. For the other
aircraft this is Conf 1. Note that the fourth combination for the A340-500/600 is
Configuration 2 at 210kts.
5.5.2 VARIOUS CONFIGURATION / SPEED COMBINATIONS
The following graphs show the holding fuel flow variation with weight for the
four different holding configurations. This is done at an altitude of 10000ft.
Effect of Holding Technique on Fuel Flow
A300B4-605R ISA F/L 100
2500
3000
3500
4000
4500
5000
90 95 100 105 110 115 120 125 130
Aircraft Weight - tonnes Fuel Flow -
kg/h
Clean Green Dot
Clean 240 kt
15/0 'S' Speed
15/0 210kt
5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy
- 64 -
This graph is for an A300 and it shows the advantage of holding in a clean
configuration at the green dot speed. The clean configuration fixed speed of 240kt
is significantly higher than the green dot speed; hence the large increase in fuel
flow with this technique. The 15/0 configuration with a fixed speed of 210kt is also
significantly higher than the ‘S’ speed, hence higher fuel flows.
The large variation in fuel flow shows how important it is to use the right
configuration and speed, compatible with the other operational requirements.
The A340-200/300 schedules the same hold speeds as the A300, and the
graphs have a similar form with a large increase in fuel flow at low weights with
the fixed speed techniques. However at high weights the difference is much
smaller. There is also a large increase when using Conf 1. Once more holding
clean at green dot speed gives the lowest fuel flow.
The following graph is for the A310 and this shows completely different
　
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