Approach Techniques Aircraft Energy Management during Approach(5)

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Conversely, when the thrust is set to fly VAPP on the glideslope, any speed loss due to a perturbation is rapidly washed out, because a lower thrust would be required to fly at this lower speed on the glideslope.
In other words, in case of perturbation, the aircraft speed tends to come back to the speed stabilized with that thrust level. The right part of the curve is called the stable part. 
On the backside of the power curve, the thrust balance is such that, at given thrust level, any tendency to decelerate increases the thrust-required-to-fly and, hence, amplifies the tendency to decelerate.
Conversely, any tendency to accelerate decreases the thrust-required-to-fly and, hence, amplifies the tendency to accelerate.
The minimum thrust speed (V minimum thrust) usually is equal to 1.35 to 1.4 V stall, in landing configuration.
The minimum final approach speed (i.e. VLS) is slightly in the backside of the power curve.
Note: On Airbus aircraft, this part of the curve is rather flat. 
 
If the airspeed drops below the final approach speed, more thrust is required to maintain the desired flight path and/or to regain the target speed.
If the thrust is set at idle, approximately 5 seconds are necessary to obtain the engine thrust required to recover from a speed loss or to initiate a go-around (as illustrated in Figure 3, Figure 4 and Figure 5).
 
 
 
 
 
Engine Acceleration Characteristics

When flying the final approach segment with the thrust set and maintained at idle (approach idle), the pilot should be aware of the acceleration characteristics of jet engines, as illustrated below.
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 3
Engine Response Scatter- Typical
The acceleration capability of high by pass ratio jet engine is dictated by its physical characteristics and controlled to:
　
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