getting to grips with COLD WEATHER OPERATIONS 寒冷天气运行(59)

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Though, the speed reduction gets its own limitation. The speeds must have some safety margins to the stall speed, minimum unstick speed (VMU) and minimum control speeds -
VMCA (Minimum Control Speed in the Air) and VMCG (Minimum Control Speed on the Ground)
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Regulations require the following:
V1 ≥ V1 limited by VMCG VR ≥ 1.05 VMCA and V2 ≥ 1.1 VMCA V2 ≥ 1.13 Vs1g for Fly-By-Wire aircraft, V2 ≥ 1.2 Vs for other aircraft.
Remark: Other conditions exist, e.g. conditions on VMU.
The first condition affects the accelerate-stop distance. The last two conditions affect the accelerate-go distance.
C6.1.3 Derated takeoff thrust
● What is a derated thrust?
Derated takeoff thrust is used to reduce the maximum thrust potentially developed by the
engines. The maximum, or no derate, thrust is named TOGA (Takeoff and Go-Around).

The dual purpose of derated thrust is to reduce the takeoff thrust, as with flexible thrust,
and to enable an increase in the takeoff weight.

Derate thrust and flexible thrust are quite often mistaken one for the other. It is beyond
the scope of this brochure to detail the differences between flexible and derated thrust.

Airbus Industrie provides different derate levels. Each derate level is certified and
associated with its own set of certified performance.
For instance, A340/A330 get derated 4%, 8%, 12%, 16%, 20% and 24%, respectively
named D04, D08, D12, D16, D20 and D24.

The main difference between .Derated. thrust and .Flexible. thrust lies in the fact that
TOGA (the full takeoff thrust) can be recovered at any moment in the case of a
flexible thrust. This explains the name .flexible thrust.: It is reduced but can be
increased at any time upon demand.
Whereas, in the case of a derated thrust, it is not allowed to revert to TOGA as long
as speed is below F (Flaps retraction speed).

Another difference is that regulations do not allow the use of flexible takeoff thrust in the
case of a contaminated runway while derated thrust is allowed. Airlines often operating in
contaminated runway conditions can still save engine life with derated thrust.

Another advantage of derated thrust is that, in some situations, it allows an increase in
takeoff weight.

● Consequence of derated thrust on takeoff weight.
The main consequence of derating the thrust
The rudder is used to counter-balance the
developed by the engines is a reduction in the
torque. Its efficiency is proportional to the
torque induced by the loss of the critical
aircraft speed. The minimum speed engine. providing efficiency high enough to control A lower torque signifies that it gets easier to safely the aircraft on the ground is VMCG control the aircraft and then a reduced VMCG (Minimum Control speed on the Ground). is achieved. Thus, each certified derated level comes with a certified VMCG.
　
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