A note on glossary terms: over the years there has been a
proliferation of aircraft weight and balance terms. This is
the result of many factors, such as the Federal Aviation
Administration (FAA) certification regulation under which
an aircraft was constructed; the FAA regulation under which
the aircraft is being operated; manufacturer standardization
agreements or a combination of these and others. Examples
of such terms are empty weight, licensed empty weight, basic
empty weight, operational empty weight, etc.
Many of these terms may have similar meanings or sound
similar. Pilots and aircraft mechanics must ensure they
understand the terminology and are applying the correct
values based on the procedure and situation dictating the
calculations undertaken.
Occasionally, the acronym “GAMA” follows the glossary
term. This indicates that it is part of the standardized format
adopted by the General Aviation Manufacturers Association
in 1976, known as GAMA Specification No.1. These aircraft
are usually manufactured under Title 14 of the Code of
Federal Regulations (14 CFR) part 23 and differ from aircraft
manufactured under the earlier certification rule Civil Air
Regulation (CAR) part 3 for weight and balance purposes
in the condition under which empty weight was established.
Aircraft certific ted under 14 CFR parts 23, 25, 27, and 29
establish their certificated empty weight as required in the
appropriate section of these regulations, which states that the
empty weight and corresponding center of gravity (CG) must
be determined by weighting the aircraft with:
• Fixed ballast
• Unusable fuel
• Full operating flu d, including oil, hydraulic flu d,
and other fluids required for normal operation of
the aircraft systems, except potable water, lavatory
precharge water, and water intended for injection in
the engine(s).
In contrast, aircraft certificated under the older CARs
established certifi ated empty weight under similar conditions
Glossary
as the newer aircraft, with the important exception that the
aircraft weight did not include full oil, only undrainable oil.
Mechanics and repair stations should consult the appropriate
certification rule when reestablishing empty weight
14 CFR part 121. The Federal regulations governing
domestic, flag, and supplemental operations
14 CFR part 135. The Federal regulations governing
commuter and on-demand operations.
Adverse loaded CG check. A weight and balance check to
determine that no condition of legal loading of an aircraft
can move the CG outside of its allowable limits.
Aircraft specifications. Documentation containing the
pertinent specifications for aircraft certificated under the
CARs.
Airplane Flight manual (AFM). An FAA-approved
document, prepared by the holder of a type certificate for an
aircraft, that specifies the operating limitations and contains
the required markings and placards and other information
applicable to the regulations under which the aircraft was
certificated
Approved type certificate. A certificate of approval issued
by the FAA for the design of an aircraft, engine, or propeller.
Arm. (GAMA) The horizontal distance from the reference
datum to the CG of an item. The algebraic sign is plus (+) if
measured aft of the datum or to the right side of the center
line when considering a lateral calculation. The algebraic
sign is minus (–) if measured forward of the datum or the left
side of the center line when considering a lateral calculation.
Balanced laterally. Being balanced in such a way that the
aircraft wings tend to remain level.
Ballast. A weight installed or carried in an aircraft to move
the center of gravity to a location within its allowable limits.
Permanent ballast (fixed ballast). A weight permanently
installed in an aircraft to bring its CG into allowable limits.
Permanent ballast is part of the aircraft empty weight.
Temporary ballast. Weights that can be carried in a cargo
compartment of an aircraft to move the location of CG for a
specifi fl ght condition. Temporary ballast must be removed
when the aircraft is weighed.
Basic empty weight. (GAMA) Standard empty weight plus
optional equipment.
Basic operating index. The moment of the airplane at its
basic operating weight divided by the appropriate reduction
factor.
Basic operating weight (BOW). The empty weight of the
aircraft plus the weight of the required crew, their baggage,
and other standard items, such as meals and potable water.
Bilge area. The lowest part of an aircraft structure in which
water and contaminants collect.
Butt (or buttock) line zero. A line through the symmetrical
center of an aircraft from nose to tail. It serves as the datum
for measuring the arms used to determine the lateral CG.
Lateral moments that cause the aircraft to rotate clockwise are
positive (+) , and those that cause it to rotate counterclockwise
are negative (–).
Calendar month. A time period used by the FAA for
certification and currency purposes. A calendar month
extends from a given day until midnight of the last day of
that month.
Civil Air Regulations (CAR). The predecessor to the Federal
Aviation Regulations.
CAM. The acronym for the manuals containing the
certification rules under the Civil Air Regulations
Center of gravity (CG). (GAMA) The point at which an
airplane would balance if suspended. Its distance from the
reference datum is determined by dividing the total moment
by the total weight of the airplane. It is the mass center of the
aircraft, or the theoretical point at which the entire weight of
the aircraft is assumed to be concentrated. It may be expressed
in percent of MAC (mean aerodynamic cord) or in inches
from the reference datum.
Center of lift. The location along the chord line of an airfoil at
which all the lift forces produced by the airfoil are considered
to be concentrated.
Centroid. The distance in inches aft of the datum of the
center of a compartment or a fuel tank for weight and balance
purposes.
CG arm. (GAMA) The arm obtained by adding the airplane’s
individual moments and dividing the sum by the total weight.
CG limits. (GAMA) The extreme CG locations within which
the aircraft must be operated at a given weight. These limits
are indicated on pertinent FAA aircraft type certificate data
sheets, specifications, or weight and balance records
CG limits envelope. An enclosed area on a graph of the
airplane loaded weight and the CG location. If lines drawn
from the weight and CG cross within this envelope, the
airplane is properly loaded.
CG moment envelope. An enclosed area on a graph of
the airplane loaded weight and loaded moment. If lines
drawn from the weight and loaded moment cross within this
envelope, the airplane is properly loaded.
Chord. A straight line distance across a wing from leading
edge to trailing edge.
Curtailment. An operator created and FAA-approved
operational loading envelope that is more restrictive than
the manufacturer’s CG envelope. It ensures that the aircraft
will be operated within limits during all phases of flight
Curtailment typically accounts for, but is not limited to, in-
flight movement of passengers and crew, service equipment,
cargo variation, seating variation, etc.
Datum. An imaginary vertical plane or line from which all
measurements of arms are taken. The datum is established
by the manufacturer. Once the datum has been selected, all
moment arms and the location of CG range are measured
from this point.
Delta (Δ). The Greek symbol “Δ” means a change in
something. ΔCG means a change in the center of gravity
location.
Dynamic load. The actual weight of the aircraft multiplied
by the load factor, or the increase in weight caused by
acceleration.
Empty weight. The weight of the airframe, engines,
all permanently installed equipment, and unusable fuel.
Depending upon the part of the federal regulations under
which the aircraft was certificated, either the undrainable oil
or full reservoir of oil is included.
Empty weight center of gravity (EWCG). This is the center
of gravity of the aircraft in the empty condition, containing
only the items specified in the aircraft empty weight. This
CG is an essential part of the weight and balance record of
the aircraft.
Empty weight center of gravity range. The distance
between the allowable forward and aft empty-weight CG
limits.
Equipment list. A list of items approved by the FAA for
installation in a particular aircraft. The list includes the name,
part number, weight, and arm of the component. Installation
or removal of an item in the equipment list is considered to
be a minor alteration.
Fleet weight. An average weight accepted by the FAA for
aircraft of identical make and model that have the same
equipment installed. When a fleet weight control program
is in effect, the fleet weight of the aircraft can be used rather
than requiring every individual aircraft to be weighed.
Fuel jettison system. A fuel subsystem that allows the fligh
crew to dump fuel in an emergency to lower the weight of an
aircraft to the maximum landing weight if a return to landing
is required before sufficient fuel is burned off. This system
must allow enough fuel to be jettisoned that the aircraft can
still meet the climb requirements specified in 14 CFR part 25.
Fulcrum. The point about which a lever balances.
Index point. A location specified by the aircraft manufacturer
from which arms used in weight and balance computations
are measured. Arms measured from the index point are called
index arms.
Interpolate. Determine a value in a range between two
known values.
Landing weight. The takeoff weight of an aircraft minus the
fuel burned and/or dumped en route.
Large aircraft (14 CFR part 1). An aircraft of more than
12,500 pounds maximum certificated takeoff weight
Lateral balance. The balance around the roll, or longitudinal,
axis.
Lateral offset moment. The moment, in pound inches, of a
force that tends to rotate a helicopter about its longitudinal
axis. The lateral offset moment is the product of the weight of
the object and its distance from butt line zero. Lateral offset
moments that tend to rotate the aircraft clockwise are positive,
and those that tend to rotate it counterclockwise are negative.
LEMAC. Leading edge of the mean aerodynamic chord. A
reference point for measurements, and specified in inches
from the datum to allow computations to relate percent MAC
to the datum.
Load cell. A component in an electronic weighing system that
is placed between the jack and the jack pad on the aircraft.
The load cell contains strain gauges whose resistance changes
with the weight on the cell.
Load factor. The ratio of the maximum load an aircraft can
sustain to the total weight of the aircraft. Normal category
aircraft must have a load factor of a least 3.8; utility category
aircraft, 4.4; and acrobatic category aircraft, 6.0.
Loading graph. A graph of load weight and load moment
indexes. Diagonal lines for each item relate the weight to the
moment index, eliminating the need for calculations.
Loading schedule. A method of calculating and documenting
aircraft weight and balance prior to taxiing to ensure the
aircraft will remain within all required weight and balance
limitations throughout the flight
Longitudinal axis. An imaginary line through an aircraft
from nose to tail, passing through its center of gravity.
Longitudinal balance. The balance around the pitch, or
lateral, axis.
MAC. Mean aerodynamic chord.
Major alteration. An alteration not listed in the aircraft,
aircraft engine, or propeller specifications (1) that might
appreciably affect weight, balance, structural strength,
performance, powerplant operation, flight characteristics,
or other qualities affecting airworthiness; or (2) that is not
done according to accepted practices or cannot be done by
elementary operations.
Maximum landing weight. (GAMA) The maximum weight
approved for the landing touchdown.
Maximum permissible hoist load. The maximum external
load that is permitted for a helicopter to carry. This load is
specified in the POH
Maximum ramp weight. (GAMA) The maximum weight
approved for ground maneuver. It includes weight of start,
taxi, and runup fuel.
Maximum takeoff weight. (GAMA) The maximum weight
approved for the start of the takeoff run.