Weight (tonnes)
65
60
55
50
Weight (tonnes)
65
60
55
50
45
45
40
40
35
35
A318 A319 (no ACT)
SYSTEMS

B. FUEL SYSTEMS

80
80
75
75
70
70
SYSTEMS
Weight (tonnes)
65
60
55
50

Weight (tonnes)
65
60
55
50
4545 4040 3535
A319 CJ (with 6 ACTs – Seq B) A320 (with 2 ACTs)
Note: On A319CJ, due to the range of the fuel vector, specific ZF envelopes have been certified in order to ensure that CG is kept inside the limits in case of failure of the fuel transfer function from the ACTs to the center tanks.

B. FUEL SYSTEMS

2.3.2. A321
The refueling sequence for the A321 and the resulting fuel vector are the following:
SYSTEMS

Fuel Weight (kg)
24000 

22000 

20000  . 

18000 

16000 

14000 . 

12000 

10000 

8000 

6000 
4000 
2000 . 

0 

.
Wing tanks (full)

2
  Center tank (full)

3
  ACTs (if applicable)

-15 -10  -5 0 5 1015
Delta Index

The following chart presents the impact of the refueling vector on the certified CG envelopes.

B. FUEL SYSTEMS

SYSTEMS

2.4. In-flight CG travel
2.4.1. A318/A319/A320
The fuel burn sequence for the A318, A319, A320 is as follows:
1/ ACTs (ACT2 then ACT1) . fuel transferred into the center tank (if applicable)
2/ center tank (until empty)
3/ inner tanks (until 750kg left in each tank)
4/ outer tanks . all the fuel transferred to the inner tanks from where it is fed to
the engines
5/ inner tanks (until empty)

The only transfer that takes place is the transfer of fuel from the outer to the inner tanks when the fuel quantity in the inner tanks reaches a low level of 750kg. The valves between the outer tanks and the inner tanks open and are latched open until the next refueling. This does not necessarily occur simultaneously in both wings. This transfer brings the CG forward.
As a consequence, the fuel vector for defueling is the same as for the refueling.
2.4.2. A321
On A321, only the wing tanks are fitted with engine feed pumps. All the fuel located in the center
and auxiliary tanks have to be pumped into the wing tanks in order to be burnt.
The fuel burn sequence is therefore the following:

1/ ACTs (ACT2 then ACT1) . fuel transferred to the center tank (if applicable) 2/ center tank . fuel transferred to the wing tanks 3/ wing tanks
So, the fuel vector is the same for refueling and defueling.

B. FUEL SYSTEMS
　
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本文鏈接地址：Getting to Grips with Aircraft Weight and Balance(23)