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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.
8. FCOM procedures require not less than a defined time before shutting
down the other engine(s) after landing. On engines with a high bypass
ratio, the cool-down time after reverse operation, prior to shut down
has a significant effect on engine life.
9. If an operator decides to use one or two engine out taxi, then FCOM
recommendations about which engine(s) to use should be followed.
4 - PRE-FLIGHT PROCEDURES Getting to grips with Fuel Economy
- 18 -
As engine-out taxi requires more thrust per engine to taxi and maneuver,
caution must be exercised to avoid excessive jet blast and FOD. More thrust is
necessary for breakaways and 180 degrees turns.
On twin-engine aircraft slow and/or tight taxi turns in the direction of the
operating engine may not be possible at high gross weight.
Single engine taxi may also be considered at low weights to avoid
excessive use of the brakes to control the acceleration tendency with all engines.
This brake use would be detrimental to carbon brake life.
The following table gives an indication of the advantages of engine out taxi
for 8 of the 12 minutes total taxi time, leaving 4 minutes warm up time.
Fuel savings with Engine out taxi
Aircraft types 12 minutes taxi
(all engines)
12 minutes taxi
(8 with engine out)
Engine Out taxi
savings
A300-600 300kg 200kg 100kg
A310 240kg 160kg 80kg
A318 120kg 80kg 40kg
A319 120kg 80kg 40kg
A320 138kg 92kg 46kg
A321 162kg 108kg 54kg
A330 300kg 200kg 100kg
A340-200/300 300kg 200kg 100kg
A340-500/600 420kg 280kg 140kg
For engine out or all engines taxi, the use of a slow taxi speed
costs fuel and time. A burst of power should be used to get the aircraft to
taxi speed, then the power should be reduced to idle. However 30kt should
not be exceeded.
Getting to grips with Fuel Economy 4 - PRE-FLIGHT PROCEDURES
- 19 -
4.5 FUEL FOR TRANSPORTATION
The normal message regarding fuel burn is that it is more economical to carry
the minimum amount required for the sector. However there are occasions
when it is economic to carry more fuel. This is when the price of fuel at the
destination airfield is significantly higher than the price at the departure
airfield.
However, since the extra fuel on board leads to an increase in fuel
consumption the breakeven point must be carefully determined.
K is the transport coefficient:
The addition of one tonne to the landing weight, means an addition of K
tonnes to the take-off weight.
For example, if K=1.3 and 1300 kg fuel is added at the departure, 1000 kg
of this fuel amount will remain at the destination. So carrying one tonne of fuel
costs 300 kg fuel more.
The extra-cost of the loaded fuel at departure is
Fuel weight x departure fuel price (ΔTOW x Pd = ΔLW x K x Pd)
The cost saving of the transported fuel is
Transported fuel x arrival price (ΔLW x Pa)
The cost due to a possible increase in flight time is
Flight time increase x cost per hour (ΔT x Ch)
It is profitable to carry extra fuel if the cost saving exceeds the extra fuel loaded
cost plus the extra time cost.
(ΔLW x Pa) >(ΔLW x K x Pd) + (ΔT x Ch)
That is to say:
ΔLW ( Pa - K x Pd) - (ΔT x Ch) > 0
LW
K TOW
Δ
= Δ
4 - PRE-FLIGHT PROCEDURES Getting to grips with Fuel Economy
- 20 -
Therefore, if ΔT=0, it is profitable to carry extra fuel if the arrival fuel price to
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