getting to grips with fuel economy(10)

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To minimize the alternate fuel, the alternate airports should be chosen as near as possible to the destination.
 
Both the JAA and FAA do not require the alternate fuel reserve in certain cases, depending on meteorological conditions and the suitability of the airport. More details are given in “Getting to Grips with Aircraft Performance”.
 
Another part of the reserves is the extra fuel, which is at the Captain’s discretion.  
There are many reasons why this extra fuel is necessary. It could be due to uncertain weather conditions or availability of alternate and destination airfields, leading to a probability of re-routing. However it is often due to lack of confidence in the flight planning and the natural desire to increase reserves.
This is the one area where a significant impact can be made through accurate flight planning. With this in place, the aircrew will see that the flight plans fuel burns are being achieved in practice. They will realize that the planned reserves are adequate and that there is no need for more.
 
4.4 TAXIING 

 
 
Good estimate of taxi times are required. Actual times need to be monitored and standard estimates changed as necessary. Jet engine performance is optimised for flight conditions, but all aircraft spend considerable time on the ground taxiing from the terminal out to the runway and back. This time has increased due to airport congestion, and increased airport size. This all leads to a waste of precious time and fuel.
 
Only using one engine for taxiing twin-engine aircraft, or two engines for four-engine aircraft can give benefits in fuel burn. Such procedures need to be considered carefully, and operators have to define their field of application.
Airbus provides standard procedures in the Flight Crew Operating Manual (FCOM) for such operations. The following factors regarding one or two engine out taxi should be considered carefully prior to its incorporation in the operators standard operating procedures: 
 
1. This procedure is not recommended for high gross weights

2. This procedure is not recommended for uphill slopes or slippery runways

3. No fire protection from ground staff is available when starting engine (s) away from the ramp

4. Reduced redundancy increases the risk of loss of braking capability and nose wheel steering.

5. FCOM procedures require not less than a defined time (from 2 to 5 minutes depending on the engine) to start the other engine(s) before take off. On engines with a high bypass ratio, warm-up time prior to applying maximum take off thrust has a significant effect on engine  life.

6. Mechanical problems can occur during start up of the other engine(s), requiring a gate return for maintenance and delaying departure time.

7. FCOM procedures require APU start before shutting down the engine after landing, to avoid an electrical transient.
　
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