getting to grips with aircraft performance 如何掌握飞机性能 2(19)

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2.2. Climb Speeds
2.2.1. Climb at Given IAS/MACH Law
A climb is generally operated at a constant Indicated Air Speed (IAS) and Mach Number. For instance, a standard climb profile for the A320 family is:
250 kt / 300 kt / M0.78
The climb phase is, therefore, divided into 3 phases (Figure G5):
.  
Below 10,000 feet: Climb at constant IAS = 250 knots. The speed is limited by Air Traffic Control (ATC) laws.

.  
Above 10,000 feet: Climb at constant IAS = 300 knots (limited to M0.78). At 10,000 feet, the aircraft accelerates to a more optimum climb speed (300 knots), which is maintained as long as the mach number remains under

.  
Above the crossover altitude: Climb at constant Mach = M0.78. The crossover altitude is the altitude where 300 knots IAS is equal to M0.78. Above this altitude, a constant ratio between the TAS and the sound velocity must be maintained to avoid high speed buffeting.

0.78.

2.2.2. Climb at Maximum Gradient
The climb gradient at green dot speed is at its maximum. Climbing at green dot speed enables a given altitude to be achieved over the shortest distance.
Green dot speed is computed by the Flight Management System based on aircraft weight, and is indicated on the Primary Flight Display (PFD) as soon as the aircraft is in clean configuration. This speed can, consequently, be easily flown in manual mode. Green dot is the target speed, in case of an engine failure after takeoff.
2.2.3. Climb at Maximum Rate
Climbing at the maximum rate of climb speed enables a given altitude to be reached in the shortest time.
The maximum rate of climb speed is not indicated on the PFD. Nevertheless, a climb at maximum rate can be carried out in managed mode (refer to “Climb at minimum cost”).
2.2.4. Climb at Minimum Cost
As seen in the “Cruise” chapter, the cost index aims at lowering direct operating costs. As a result, for a given cost index, an optimum climb speed (IASECON) and an optimum climb mach number (MachECON) are calculated by the FMGS as a function of the aircraft’s weight. The climb is then carried out in managed mode, based on the following IAS/Mach law:

250 kt / IASECON / MachECON
To minimize overall fuel consumption during flight, a low cost index must be used. As the climb phase is fuel consuming, it is advantageous to minimize climb duration. This is achieved at the maximum rate of climb speed.
CI = 0 .
 IASECON = Maximum rate of climb speed
On the other hand, a higher cost index provides a higher climb speed, thus lowering the rate of climb. But the distance covered during the climb is longer, so the cruise phase and total flight time are reduced. The maximum climb speed is generally limited to VMO -10 knots.
CI = CImax .
 IASECON = VMO – 10 kt
2.3. FCOM Climb Table

 IN FLIGHT PERFORMANCE CLIMB  3.05.10  P 3 
　
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