5. BALANCE CALCULATION METHODS
5.1. Introduction
It is necessary to determine, before takeoff, the center of gravity position of the aircraft. The main reason is the flight safety. Indeed, it is necessary to ensure that the aircraft CG will remain within pre-determined limits during the whole flight. Another reason is an operational reason: the crew must be able to correctly trim the aircraft for takeoff by selecting the appropriate THS (Trimmable Horizontal Stabilizer) angle, directly deduced from the center of gravity position of the aircraft. An aircraft is a combination of several items that have a particular weight and a particular location. Different methods are available to determine the influence of each item on the aircraft balance:
1 Manual method : Balance chart / Balance table
2 EDP method
5.2. Manual balance calculation method
5.2.1. Balance chart
C. Operational Loading Documents
. Balance chart example
LOADING LOADING
C. Operational Loading Documents
. Fuel index table example
IATA AHM 519 gives information about the kind of information that must appear on a balance chart:
A – The type of aircraft and version
B – A drawing of the aircraft layout showing : . The passenger cabin section . The position and numbering of holds and compartments
C – Index units as the first scale
D – For each compartment or cabin section : . Vertical or sloping lines corresponding to index variations . Arrows indicating direction and value of each pitch
E – A balance diagram with shaded areas outside the forward and aft balance limits
F – The influence of fuel on weight and balance. It can be provided on a separate fuel index table
G – Final ZFW and TOW CG values in percentage of the Mean Aerodynamic Chord (%MAC).
Other optional information may appear on the balance chart, according to carriers requirements:
H – Index formula for DOW Index calculation(1)
I – Weight deviations in galley zones and effect on balance
J – Weight information(2)
K– Pitch Trim scale for THS setting
(1) For a given aircraft, it’s possible to start the balance calculation from the Dry Operating Index (DOI) or from the combination DOW / DOW H-arm. Thus, the index formula is only required for the second case.
(2)When this information appears on the balance chart, this one can be called a “Load and Trim sheet”
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C. Operational Loading Documents
. Numerical example:
DOW conditions: Weight : 123 500 kgData coming from the weighingH-arm : 33.378 m
.
report (refer to WBM)
Weight deviations : Zone E : +150 kgPantry adjustment in the galleyZone F: +150 kg
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