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Above 24,000 ft to 34,000 ft inclusive 265 KT 240 KT 265 KT 265 KT
Above 34,000 ft M 0.83 240 KT 265 KT M 0.83
If green dot is higher than these maximum recommended speeds, it is
advised to hold in configuration 1 at “S” speed below 20000ft: keeping clean
configuration coupled with a speed reduction would save fuel but would decrease
the speed margins which are especially important in turbulent conditions.
5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy
- 68 -
5.5.3 LINEAR HOLDING
If holding is going to be necessary, linear holding at cruise flight level and at
green dot speed should be performed whenever possible since total flight time will
remain constant (cruise time is increased but holding time is reduced) and fuel
flow is lower at high flight levels.
If A.T.C. informs 15 minutes before reaching a fix and that 10 minutes
holding is expected. Two options are possible:
• The aircraft is flown 15 minutes at cruise speed and holds for 10 minutes at
green dot speed.
• The aircraft performs the cruise to reach the fix at green dot speed and
holds for the remaining time at the same speed.
10 minutes holding
at green dot speed
15 minutes at cruise
d
Holding at cruise
Holding for remaining
time at green dot speed
Cruise at green dot speed
Holding optimization
Getting to grips with Fuel Economy IN FLIGHT PROCEDURES
- 69 -
ATC restrictions may not permit a cruise speed reduction at the cruise flight
level, or permit a hold at the cruise flight level. The standard procedure would be
to continue to the top of descent at cruise speed and descend to a flight level to
join the stack. However if ATC permit a linear hold it can give significant fuel
savings.
However the amount of savings is very dependant on the characteristics of
the aircraft type. The increase in time in the cruise depends on how much slower
green dot speed is compared to the normal cruise speed. This increase was much
higher with the A320 than the A340. In addition, most aircraft, flying the same
cruise distance at green dot speed actually uses a little more fuel at these
altitudes. The following table shows the gains due to cruising slower and
spending less time in the hold at the cruise flight level.
Advantages of a 15min linear hold at cruise altitude at Green Dot speed
Aircraft type Weight kg
Cruise
Flight Level
Cruise
Speed
Fuel
savings kg
A300 120000 350 0.8 95
A310 110000 350 0.8 115
A318 50000 350 0.78 120
A319 50000 350 0.78 135
A320 60000 350 0.78 80
A321 70000 350 0.78 50
A330 180000 390 0.82 95
A340-200 200000 390 0.82 10
A340-300 200000 390 0.82 45
A340-500/600 270000 390 0.82 5
The high green dot speed for the A340 leads to very little advantage in linear
holding. However the other aircraft show significant benefits.
If the increase in cruise time can be used to reducing the time in the holding
pattern or stack, then the benefits will be similar to those shown in the table
above. However the constraints of ATC are unlikely to let these benefits accrue.
5 - IN FLIGHT PROCEDURES Getting to grips with Fuel Economy
- 70 -
5.6 APPROACH
5.6.1 FLIGHT PATH PRIOR TO GLIDE SLOPE INTERCEPTION
Procedures used in the approach phase can affect the amount of fuel
consumed in this phase of the flight. The glide slope can be intercepted either
horizontally between 1500ft and 2000ft or in a descending flight path above
2000ft. This latter method uses less fuel, but the amount is difficult to quantify, as
it depends on the exact flight paths in each case. However, the most important
feature of an approach is that it should be well executed, stabilized and safe.
None of these features should be compromised in an attempt to save fuel, and the
procedure flown should be that appropriate to the airport, runway, equipment,
conditions, etc.
5.6.2 LANDING GEAR EXTENSION
The standard procedure is that Gear Down is selected down when Conf 2 (or
flap 20 for A300/310) is achieved. The effect of extending the gear prior to this
point will increase fuel burn, but the amount is difficult to quantify without
knowing when the gear is extended. However, the most important feature of an
approach is that it should be well executed, stabilized and safe. The use of gear is
often one of the means of achieving this through speed control, and gear
extension should not be delayed to save fuel.
Getting to grips with Fuel Economy 6 - DETAILED SUMMARY
- 71 -
6. DETAILED SUMMARY
6.1 INTRODUCTION
In this brochure it can be seen that there are many ways of influencing the
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