Embraer EMB145 - Page 967

AIRPLANE
OPERATIONS
MANUAL
WEIGHT AND
BALANCE
REVISION 31
1-06-40
Page
1
Code
03
CENTER OF GRAVITY CURTAILMENTS
The airplane weight and balance calculations are normally performed
assuming that passengers are evenly distributed along the airplane
cabin and that the crew, passengers and movable items are fixed in a
pre-determined position.
For all practical purposes, however, it is known that passengers may
not be evenly seated, flight attendants move along the cabin, the
landing gear retracts, etc. All these movements, not previously
expected in the weight and balance calculations, may result in
deviations from the assumed load distribution.
For these reasons, some aeronautical authorities (including FAA
AC120-27E) require that airlines use an Operational CG envelope,
which is the AFM certified CG envelope reduced by a CG margin to
account for the possible deviations from the assumed load distribution.
This process is known as Center of Gravity Curtailment.
There are 3 basic types of CG curtailments:
• Takeoff and landing allowances: These are the deviations that
affect the CG position for takeoff and landing. Uneven distribution of
passengers, flap and landing gear movement and cargo/baggage
shift are considered takeoff and landing allowances.
• Flight allowances: These are the deviations that affect the CG
position in flight. All takeoff and landing allowances plus flight
attendant and catering service movement are considered in-flight
allowances.
• Fuel allowances: If the airline does not wish to check the CG
position at the landing weight, it is necessary to consider a fuel
allowance due to CG shift caused by the reduction of fuel quantity
during the flight. In addition, it may be necessary to consider an
allowance due to variations in the fuel density.
The CG curtailment process is a critical procedure because the
amount of CG margin (curtailment) depends on the possible deviations
considered by the airline. If excessive deviations (allowances) are
considered by the airline, a very thin Operational CG envelope may be
obtained, resulting in huge difficulties to balance the airplane during
airline operations. On the other hand, if few deviations (allowances) are
considered, a large Operational CG envelope is obtained, but safety
may be jeopardized by CG deviations from the assumed load
distribution.