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If the FOB entry is not correct, the GW and CG will not be correct until the engines are started, and
all of the above-mentioned consequences apply. When the engines are started, fuel figures are
updated and applicable data is also updated accordingly.
A330/A340 FLIGHT CREW TRAINING MANUAL
SUPPLEMENTARY INFORMATION
ZFW- ZFCG ENTRY ERRORS
A330/A340 FLEET SI-040 P 4/4
FCTM 17 JUN 09
OPERATIONAL RECOMMENDATIONS
Applicable to: ALL
It is possible to limit the number of ZFW or ZFWCG entry errors by applying the following
recommendations:
• If the flight crew performs a manual refuelling, the flight crew should carefully check the CG
calculation, because the load and trim sheet CG is calculated on the basis of the standard
distribution of fuel.
• Both flight crewmembers should crosscheck ZFW and ZFWCG entries.
• The CG on the load and trim sheet should be compared with the CG on the ECAM.
If the flight crew detects a GW error in flight (e.g. a characteristic speeds error), then a GW update
can be made via the FUEL PRED page of the MCDU.
A330/A340 FLIGHT CREW TRAINING MANUAL
SUPPLEMENTARY INFORMATION
CENTRE OF GRAVITY
A330/A340 FLEET SI-050 P 1/10
FCTM 17 JUN 09
PREFACE
Applicable to: ALL
The Center of Gravity (CG) is the point at which weight is applied. The CG is expressed as a
percentage of the Mean Aerodynamic Chord (MAC). It must remain within a range determined by the
CG's impact on the aircraft:
• Performance
• Structure
• Handling characteristics (when in direct law).
These factors define the range that the CG must remain within. This range is referred to as the CG
envelope.
MECHANICAL ASSUMPTIONS
Applicable to: ALL
For pitch control, there are three forces that must be considered when airborne:
• The weight applied on the CG
• The lift applied on the Center of Pressure (CP)
• The downward force created by the Trimmable Horizontal Stabilizer (THS).
Forces applied on flying aircraft
Because the first two forces are not applied at the same point, they create a pitching moment, that
must be counteracted by the THS setting.
INFLUENCE OF THE CENTER OF GRAVITY ON THE AIRCRAFT PERFORMANCE
Applicable to: ALL
The position of the CG has a significant impact on performance, because it determines the balance
of the longitudinal forces.
A330/A340 FLIGHT CREW TRAINING MANUAL
SUPPLEMENTARY INFORMATION
CENTRE OF GRAVITY
A330/A340 FLEET SI-050 P 2/10
FCTM 17 JUN 09
When the CG moves forward, the nose down moment increases. The THS produces a greater
downward force to counteract this moment. As a result, lift must increase, in order to balance both
the weight and the THS downward force. Therefore, a forward CG will result in a greater stall speed
value. On A330/A340, the stall speed increases by 1.5 kt, when the CG varies from 26 % to full
forward CG.
influence of the CG position
IMPACT ON TAKEOFF PERFORMANCE
TAKEOFF SPEED AND ASSOCIATED DISTANCES
The aircraft operating speeds are referenced to the stall speed, e.g. V2 >1.13 VS1G.
If the CG moves forward ▸ VS1G increases ▸ V2 increases ▸ TOD increases (or the
runway-limited TOW decreases).
ROTATION MANEUVER
An aft CG gives the aircraft a nose up attitude, that helps the rotation. A forward CG results in a
nose heavy situation, and a difficult rotation. It is "heavier", therefore longer, at forward CG.
CLIMB GRADIENT
As mentioned above, a forward CG is counteracted by a greater THS downward force.
This creates drag, that, in addition to the drag caused by the lift increase, degrades aircraft
performance, for example, the climb gradient.
For example:
A340 Performance decrement with CG full forward, in comparison with CG 26 % CONF. 3, Packs On, ISA, Zp=0
CG 26 % CG full forward
TOD 3 165 m 3 241 m 76 m
5 % Climb gradient limiting weight 257.6 t 256.2 t 1.4 t
A330/A340 FLIGHT CREW TRAINING MANUAL
SUPPLEMENTARY INFORMATION
CENTRE OF GRAVITY
A330/A340 FLEET SI-050 P 3/10
FCTM 17 JUN 09
IMPACT ON IN-FLIGHT PERFORMANCE
A forward CG causes a nose up counter moment, that degrades fuel consumption, because
of increased induced drag. For low fuel consumption, it is better to have the CG as far aft as
possible.
Fuel increment 1 000 nm stage length CG location at 20 % (reference at 35 %)
Aircraft type Fuel increment (kg/lb)
A330 220/485
A340 380/838
The result summarizes the worst cases, i.e. it considers an heavy aircraft at a high flight level.
Airbus has developed a trim tank transfer system, that controls the aircraft CG. When the airplane
　
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