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occupant load have a very limited effect on the balance
of the aircraft. Aircraft of such a configuration show an
EWCG range in the TCDS. [Figure 5-5] If the EWCG is
located within this range, it is impossible to legally load
the aircraft so that its loaded CG will fall outside of its
allowable range.
If the TCDS list an empty-weight CG range, and after the
alteration is completed the EWCG falls within this range,
then there is no need to compute a fore and aft check for
adverse loading.
But if the TCDS lists the EWCG range as “None” (and
most of them do), a check must be made to determine
whether or not it is possible by any combination of legal
loading to cause the aircraft CG to move outside of either
its forward or aft limits.
Adverse-Loaded CG Checks
Many modern aircraft have multiple rows of seats and
often more than one baggage compartment. After any
repair or alteration that changes the weight and balance,
the A&P mechanic or repairman must ensure that no
legal condition of loading can move the CG outside of its
allowable limits. To determine this, adverse-loaded CG
checks must be performed and the results noted in the
weight and balance revision sheet.
Figure 5-4. Weight and moment index changes caused by a typical alteration.
Figure 5-5. Typical notation in a TCDS when an aircraft has an
empty-weight CG range.
5–
Figure 5-6. Weight and balance information used for adverse-loaded
CG Checks.
Figure 5-7. Loading diagram for adverse-loaded CG check.
Forward Adverse-Loaded CG Check
To conduct a forward CG check, make a chart that includes
the airplane and any occupants and items of the load
located in front of the forward CG limit. [Figure 5-7]
Include only those items behind the forward limit that are
essential to flight. This is the pilot and the minimum fuel.
In this example, the pilot, whose nominal weight is 170
pounds, is behind the forward CG limit. The fuel is also
behind the forward limit, so the minimum fuel is used. For
weight and balance purposes, the minimum fuel is no more
than the quantity needed for one-half-hour of operation
at rated maximum continuous power. This is considered
to be 1/12 gallon for each maximum except takeoff
(METO) horsepower. Because aviation gasoline weighs 6
pounds per gallon, determine the number of pounds of the
minimum fuel by dividing the METO horsepower by 2; in
this example minimum fuel is 115 pounds.
The front and rear seats and the baggage are all behind
the forward CG limit, so no passengers or baggage are
considered.
Make a chart like the one in Figure 5-8 to determine the
CG with the aircraft loaded for its most forward CG.
With the load consisting of only a pilot and the minimum
fuel, the CG is +36.6, which is behind the most forward
allowable limit for this weight of +33.0.
Figure 5-8. Load conditions for forward adverse-loaded CG check.
5–
Aft Adverse-Loaded CG Check
To conduct an aft, or rearward, CG check, make a chart
that includes the empty weight and EWCG of the aircraft
after the alteration, and all occupants and items of the load
behind the aft CG limit of 46.0. The pilot is in front of
this limit, but is essential for flight and must be included.
In this example, only the pilot will occupy the front seats.
Since the CG of the fuel is behind the aft limit, full fuel
will be used as well as the nominal weight (170 lbs) for
both rear seat passengers and the maximum allowable
baggage.
Under these loading conditions, the CG is located at +45.8,
which is ahead of the aft limit of +46.0. [Figure5-9]
With only the pilot in front of the aft CG limit and
maximum of all items behind the aft limit, the CG will be
at +45.8 inches, which is ahead of the aft limit of +46.0
inches.
Ballast
It is possible to load most modern airplanes so the center
of gravity shifts outside of the allowable limit. Placards
and loading instructions in the Weight and Balance Data
inform the pilot of the restrictions that will prevent such
a shift from occurring. A typical placard in the baggage
compartment of an airplane might read:
When rear row of seats is occupied, 120
pounds of baggage or ballast must be carried
in forward baggage compartment. For
additional loading instructions, see Weight
and Balance Data.
When the CG of an aircraft falls outside of the limits, it
can usually be brought back in by using ballast.
Temporary Ballast
Temporary ballast, in the form of lead bars or heavy
canvas bags of sand or lead shot, is often carried in the
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Aircraft Weight and Balance Handbook(21)
