Weight Changes

Weight Changes

The maximum allowable weight for an aircraft is
determined by design considerations. However, the
maximum operational weight may be less than the
maximum allowable weight due to such considerations as
high-density altitude or high-drag field conditions caused
by wet grass or water on the runway. The maximum
operational weight may also be limited by the departure or
arrival airport’s runway length.

One important preflight consideration is the distribution
of the load in the aircraft. Loading the aircraft so the gross
weight is less than the maximum allowable is not enough.
This weight must be distributed to keep the CG within the
limits specified in the POH or AFM.

If the CG is too far forward, a heavy passenger can
be moved to one of the rear seats or baggage can be
shifted from a forward baggage compartment to a rear
compartment. If the CG is too far aft, passenger weight or
baggage can be shifted forward. The fuel load should be
balanced laterally: the pilot should pay special attention
to the POH or AFM regarding the operation of the fuel
system, in order to keep the aircraft balanced in flight.

Weight and balance of a helicopter is far more critical
than for an airplane. With some helicopters, they may be
properly loaded for takeoff, but near the end of a long
flight when the fuel tanks are almost empty, the CG may
have shifted enough for the helicopter to be out of balance
laterally or longitudinally. Before making any long flight,
the CG with the fuel available for landing must be checked
to ensure it will be within the allowable range.

Airplanes with tandem seating normally have a limitation
requiring solo flight to be made from the front seat in
some airplanes or the rear seat in others. Some of the
smaller helicopters also require solo flight be made from a
specific seat, either the right, left, or center. These seating
limitations will be noted by a placard, usually on the
instrument panel, and they should be strictly adhered to.

As an aircraft ages, its weight usually increases due to
trash and dirt collecting in hard-to-reach locations, and
moisture absorbed in the cabin insulation. This growth in
weight is normally small, but it can only be determined by
accurately weighing the aircraft

Changes of fixed equipment may have a major effect upon
the weight of the aircraft. Many aircraft are overloaded by
the installation of extra radios or instruments. Fortunately,
the replacement of older, heavy electronic equipment with
newer, lighter types results in a weight reduction. This
weight change, however helpful, will probably cause the
CG to shift and this must be computed and annotated in
the weight and balance record.

Repairs and alteration are the major sources of weight
changes, and it is the responsibility of the A&P mechanic
or repairman making any repair or alteration to know the
weight and location of these changes, and to compute the
CG and record the new empty weight and EWCG in the
aircraft weight and balance record.

If the newly calculated EWCG should happen to fall
outside the EWCG range, it will be necessary to perform
adverse loading check. This will require a forward and
rearward adverse-loading check, and a maximum weight
check. These weight and balance extreme conditions
represent the maximum forward and rearward CG position
for the aircraft. Adverse loading checks are a deliberate
attempt to load an aircraft in a manner that will create the
most critical balance condition and still remain within
the design CG limits of the aircraft. If any of the checks
fall outside the loaded CG range, the aircraft must be
reconfigured or placarded to prevent the pilot from loading
the aircraft improperly. It is sometimes possible to install
fixed ballast in order for the aircraft to again operate within
the normal CG range.

The A&P mechanic or repairman conducting an annual or
condition inspection must ensure the weight and balance
data in the aircraft records is current and accurate. It
is the responsibility of the pilot in command to use the
most curre hands off the controls. Longitudinal stability
is maintained by ensuring the CG is slightly ahead of the
center of lift. This produces a fixed nose-down force independent of
the airspeed. This is balanced by a variable nose-up force,
which is produced by a downward aerodynamic force on
the horizontal tail surfaces that varies directly with the
airspeed.