Approach Techniques Aircraft Energy Management during Approach(4)

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In order to be stabilized at 130 kt at 1000 above airfield elevation, the maximum speed that can be accepted and maintained down to the OM is: 130 kt + 30 kt = 160 kt.
 
 
 
 
 
 
Figure 1
Deceleration along Glide Slope - Typical
Note: The OM may be located from 4 to 6 NM from the runway threshold. 
 
Whenever being required to maintain a high speed down to the marker, the above quick computation may be considered for assessing the feasibility of the ATC request.

 

 

Avoiding the Back Side of the Power Curve

During an unstable approach, the airspeed or the thrust setting often is observed to deviate from the target values:
Airspeed is below the target final approach speed (VAPP); and/or,

Thrust is reduced and maintained at idle.

Thrust-required-to-fly Curve

 

Figure 2 illustrates the “thrust-required-to-fly” curve (i.e. the power curve).
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 2
Power Curve – Typical
The power curve is divided in two parts:
The left side of the power curve, called the backside of the power curve;

The right side of the power curve.

The difference between the available-thrust and the thrust-required-to-fly  (i.e., the thrust balance):
Represents the climb or acceleration capability (if the available-thrust exceeds the required-thrust); or,

Indicates that speed and/or flight path cannot be maintained (if the required-thrust exceeds the available-thrust).

The right part of the power curve is the normal area of operation.
The thrust balance is such that, when the thrust is set to fly VAPP on the glideslope, any increase of the aircraft speed due to a perturbation is rapidly washed out, because a higher thrust would be required to fly at this higher speed on the glideslope.
　
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