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• Providing information to the flight crew that allows them
to fuel and load the aircraft to carry the maximum
payload without exceeding either the maximum takeoff
or landing weights.
This handbook contains information about the adjustment of
the elevator trim for takeoff based on the takeoff weight and
CG location, as well as information regarding the fuel
dumping time needed to reduce the weight of the airplane to
its allowable landing weight in an emergency situation.
Weighing Requirements
FAA-approved operating manuals describe the requirements
for weighing the aircraft. These manuals may specify that
each individual aircraft be weighed, or they may allow fleet
weight to be used if the operator has several aircraft of the
same model and configuration, with the same equipment
installed on each.
Individual Aircraft Weight
Before an aircraft is placed into service, it should be weighed
and the empty weight and CG location established. New
aircraft are normally weighed at the factory and may be placed
in service without reweighing, if the weight and balance
records have been adjusted for alterations or modifications
to the aircraft.
However, the Operation Specifications under which some
large aircraft are operated mandate that the aircraft be reweighed
at specified intervals, and it is important when an
aircraft is transferred from one operator to another that the
regulations regarding reweighing be observed.
Large aircraft: An aircraft of more
than 12,500 pounds, maximum
certificated takeoff weight.
6– 2
Locating and Monitoring Weight
and CG Location
It is important that the flight crew have access to the most
current weight and balance records containing the empty
weight and the EWCG. Without this basic information, loaded
weight and balance computations cannot produce accurate
results.
Determining the Empty Weight and EWCG
When the aircraft is properly prepared for weighing ( see Page
3-2), roll it onto the scales and level it. The weights are
measured at three weighing points: the two main wheel points
and the nose wheel point.
The empty weight and EWCG are determined by using the
following steps, and the results are recorded in the weight and
balance record for use in all future weight and balance
computations.
1. Determine the moment index of each of the main-wheel
weighing points by multiplying the net weight (scale
reading less tare weight), in pounds, at these points by
the distance from the datum, in inches. Divide these
numbers by the appropriate reduction factor.
2. Determine the moment index of the nose wheel weighing
point by multiplying its net weight, in pounds, by its distance
from the datum, in inches. Divide this by the
reduction factor.
3. Determine the total weight by adding the net weight of
the three weighing points and the total moment index by
adding the moment indexes of each point.
4. Divide the total moment index by the total weight, and
multiply this by the reduction factor. This gives the CG
in inches from the datum.
5. Determine the distance of the CG behind the leading edge
of the mean aerodynamic chord (LEMAC) by subtracting
the distance between the datum and LEMAC from the
distance between the datum and the CG.
Distance CG to LEMAC = Datum to CG – Datum to
LEMAC
6. Determine the EWCG in % MAC by using this formula:
Tare weight: The weight of all
chocks and other items used to
secure an aircraft on the scales for
weighing.
Net weight: The scale readings taken
when weighing an aircraft less the
weight of any chocks or other
devices used to hold the aircraft on
the scales.
Reduction factor: A number,
usually 100 or 1,000 by which a
moment is divided to produce a
smaller number that is less likely to
cause mathematical errors when
computing the center of gravity.
Moment index: The moment
(weight times arm) divided by a
reduction factor such as 100 or 1,000
to make the number smaller and
reduce the chance of mathematical
errors in computing the center
of gravity.
Fleet Weights
To establish a fleet weight for a group of aircraft of the same
model and configuration, with the same equipment installed
in each, several aircraft must be weighed and an average
operating weight determined. The number of aircraft weighed
depends upon the size of the fleet. The FAA recommends in
AC 120-27, Aircraft Weight and Balance Control, that these
numbers range from all the aircraft in a fleet of three or less
to more than six aircraft in fleets of more than nine. The
　
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