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Pilot's Handbook of Aeronautical Knowledge
Weight and Balance
Balance, Stability, and Center of Gravity

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Pilot's Handbook of Aeronautical Knowledge



Table of Contents

Chapter 1, Introduction To Flying
Chapter 2, Aircraft Structure
Chapter 3, Principles of Flight
Chapter 4, Aerodynamics of Flight
Chapter 5, Flight Controls
Chapter 6, Aircraft Systems
Chapter 7, Flight Instruments
Chapter 8, Flight Manuals and Other Documents
Chapter 9, Weight and Balance
Chapter 10, Aircraft Performance
Chapter 11, Weather Theory
Chapter 12, Aviation Weather Services
Chapter 13, Airport Operation
Chapter 14, Airspace
Chapter 15, Navigation
Chapter 16, Aeromedical Factors
Chapter 17, Aeronautical Decision Making




Terms and Definitions
The pilot should be familiar with terms used in working
problems related to weight and balance. The following list
of terms and their definitions is standardized, and knowledge
of these terms aids the pilot to better understand weight and
balance calculations of any aircraft. Terms defined by the
General Aviation Manufacturers Association (GAMA) as
industry standard are marked in the titles with GAMA.

• Arm (moment arm)—the horizontal distance in inches
from the reference datum line to the CG of an item. The
algebraic sign is plus (+) if measured aft of the datum,
and minus (–) if measured forward of the datum.
• Basic empty weight (GAMA)—the standard empty
weight plus the weight of optional and special
equipment that have been installed.
• Center of gravity (CG)—the point about which an
aircraft would balance if it were possible to suspend
it at that point. 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 inches from the reference datum, or in
percent of MAC. The CG is a three-dimensional point
with longitudinal, lateral, and vertical positioning in
the aircraft.
• CG limits—the specified forward and aft points
within which the CG must be located during flight
These limits are indicated on pertinent aircraft
• CG range—the distance between the forward and aft CG
limits indicated on pertinent aircraft specifications.
• Datum (reference datum)—an imaginary vertical plane
or line from which all measurements of arm 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—a Greek letter expressed by the symbol to
indicate a change of values. As an example, CG
indicates a change (or movement) of the CG.
• Floor load limit—the maximum weight the floor
can sustain per square inch/foot as provided by the
• Fuel load—the expendable part of the load of the
aircraft. It includes only usable fuel, not fuel required
to fill the lines or that which remains trapped in the
tank sumps.
• Licensed empty weight—the empty weight that
consists of the airframe, engine(s), unusable fuel, and
undrainable oil plus standard and optional equipment
as specified in the equipment list. Some manufacturers
used this term prior to GAMA standardization.

• Maximum landing weight—the greatest weight that
an aircraft normally is allowed to have at landing.
• Maximum ramp weight—the total weight of a loaded
aircraft, and includes all fuel. It is greater than the
takeoff weight due to the fuel that will be burned during
the taxi and runup operations. Ramp weight may also
be referred to as taxi weight.
• Maximum takeoff weight—the maximum allowable
weight for takeoff.
• Maximum weight—the maximum authorized weight
of the aircraft and all of its equipment as specified in
the TCDS for the aircraft.
• Maximum zero fuel weight (GAMA)—the maximum
weight, exclusive of usable fuel.
• Mean aerodynamic chord (MAC)—the average
distance from the leading edge to the trailing edge of
the wing.
• Moment—the product of the weight of an item
multiplied by its arm. Moments are expressed in
pound-inches (in-lb). Total moment is the weight of
the airplane multiplied by the distance between the
datum and the CG.
• Moment index (or index)—a moment divided by a
constant such as 100, 1,000, or 10,000. The purpose of
using a moment index is to simplify weight and balance
computations of aircraft where heavy items and long
arms result in large, unmanageable numbers.
• Payload (GAMA)—the weight of occupants, cargo,
and baggage.
• Standard empty weight (GAMA)—aircraft weight
that consists of the airframe, engines, and all items of
operating equipment that have fixed locations and are
permanently installed in the aircraft, including .xed
ballast, hydraulic fluid, unusable fuel, and full engine
• Standard weights—established weights for numerous
items involved in weight and balance computations.
These weights should not be used if actual weights are
available. Some of the standard weights are:
Gasoline ............................................... 6 lb/US gal
Jet A, Jet A-1 .................................... 6.8 lb/US gal
Jet B ...................................................6.5 lb/US gal
Oil ......................................................7.5 lb/US gal
Water .....................................................8.35 lb/US gal
• Station—a location in the aircraft that is identified by
a number designating its distance in inches from the
datum. The datum is, therefore, identified as station
zero. An item located at station +50 would have an
arm of 50 inches.
• Useful load—the weight of the pilot, copilot,
passengers, baggage, usable fuel, and drainable oil. It is
the basic empty weight subtracted from the maximum
allowable gross weight. This term applies to general
aviation (GA) aircraft only.