Thrust required - in %
The right side of the power curve is the normal zone of operation.
The thrust balance is such that, at given thrust level, any tendency to accelerate increases the thrust-required-to-fly and, hence, brings back the aircraft to the initial airspeed.
Conversely, any tendency to decelerate decreases the thrust-required-to-fly and, hence, brings back the aircraft to the initial airspeed
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 is slightly in the backside of the power curve.
If the airspeed is allowed to decrease below the final approach speed, more thrust is required to maintain the desired flight path and/or to regain the target speed.
In addition, if the thrust is set and maintained at idle, no energy is immediately available to recover from a low speed condition or to initiate a go-around (as illustrated in Figure 3, Figure 4 and Figure 5).
Energy Management during Approach
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AIRBUS INDUSTRIE
 Flight Operations Support
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.
Thrust Response from Idle to GA Thrust
( typical engine-to-engine scatter )

Getting to Grips withApproach-and-Landing Accidents Reduction
The aircraft certification (FAR – Part 25) ensures that the thrust achieved after 8 seconds (starting from flight/approach idle) allows a minimum climb gradient of 3.2 % for go-around.
Thrust Response - Approach Idle to GA
( aicraft certification requirements )
100

Approach idle
0 0 1 2 3 4 5 6 7 8 910 Time ( seconds )

Figure 3                  Engine Response Scatter- Typical
The acceleration capability of a jet engine is controlled to:
.  
Protect the engine against a stall or flameout; and,

.  
Comply with the engine and aircraft certification requirements ( U.S. FAR – Part 33 and FAR – Part 25, respectively, or the applicable equivalent regulation).

The engine certification (FAR – Part 33) ensures a time of 5 seconds or less to accelerate from 15% to 95 % of the go-around thrust.
Thrust ( in % GA thrust )
60 40 20

Thrust ( in % of GA thrust )
80
60
40
20

0 0 12345678910
Time ( seconds )
Figure 4                 Certified Thrust Response -Typical

Energy Management during Approach
Page 5

AIRBUS INDUSTRIE Getting to Grips with
 Flight Operations Support Approach-and-Landing Accidents Reduction

Go-around from low speed/low thrust:
Table 1 indicates the thrust required (in % of the Figure 5 illustrates the consequences associated
TOGA thrust) during the transition from a stabilized with flying an approach with:
approach to a go-around.

.  
Speed below the target final approach speed ( V APP ); and/or,

.  
Thrust not stabilized or set and maintained at idle.

% of TOGA Thrust 
Stabilized approach 3-degree glide path / V APP  20 % 
Arresting altitude loss  30 % 
“Positive Climb”  > 30 % 
　
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