Management of Weight and Balance Control
Title 14 of the Code of Federal Regulations (14 CFR) part 23,
section 23.23 requires establishment of the ranges of weights
and CGs within which an aircraft may be operated safely. The
manufacturer provides this information, which is included in
the approved AFM, TCDS, or aircraft specifications.
While there are no specified requirements for a pilot operating
under 14 CFR part 91 to conduct weight and balance
calculations prior to each flight, 14 CFR part 91, section
91.9 requires the pilot in command (PIC) to comply with the
operating limits in the approved AFM. These limits include
the weight and balance of the aircraft. To enable pilots to
make weight and balance computations, charts and graphs
are provided in the approved AFM.
Weight and balance control should be a matter of concern to
all pilots. The pilot controls loading and fuel management
(the two variable factors that can change both total weight
and CG location) of a particular aircraft. The aircraft owner
or operator should make certain that up-to-date information
is available for pilot use, and should ensure that appropriate
entries are made in the records when repairs or modifications
have been accomplished. The removal or addition of
equipment results in changes to the CG.
Weight changes must be accounted for and the proper
notations made in weight and balance records. The
equipment list must be updated, if appropriate. Without such
information, the pilot has no foundation upon which to base
the necessary calculations and decisions.
Standard parts with negligible weight or the addition of minor
items of equipment such as nuts, bolts, washers, rivets, and
similar standard parts of negligible weight on fixed-wing
aircraft do not require a weight and balance check. The
following criteria for negligible weight change is outlined
in Advisory Circular (AC) 43.13-1 (as revised), Methods
Techniques and Practices—Aircraft Inspection and Repair:
• One pound or less for an aircraft whose weight empty
is less than 5,000 pounds
• Two pounds or less for aircraft with an empty weight
of more than 5,000 pounds to 50,000 pounds
• Five pounds or less for aircraft with an empty weight
of more than 50,000 pounds
Negligible CG change is any change of less than 0.05 percent
Mean Aerodynamic Chord (MAC) for fixed-wing aircraft
or 0.2 percent for rotary wing aircraft. MAC is the average
distance from the leading edge to the trailing edge of the
wing. Exceeding these limits would require a weight and
balance check.
Before any flight, the pilot should determine the weight
and balance condition of the aircraft. Simple and orderly
procedures based on sound principles have been devised
by the manufacturer for the determination of loading
conditions. The pilot uses these procedures and exercises
good judgment when determining weight and balance. In
many modern aircraft, it is not possible to fill all seats,
baggage compartments, and fuel tanks, and still remain within
the approved weight and balance limits. If the maximum
passenger load is carried, the pilot must often reduce the fuel
load or reduce the amount of baggage.
14 CFR part 125 requires aircraft with 20 or more seats
or maximum payload capacity of 6,000 pounds or more
to be weighed every 36 calendar months. Multi-engine
aircraft operated under 14 CFR part 135 are also required
to be weighed every 36 months. Aircraft operated under 14
CFR part 135 are exempt from the 36 month requirement
if operated under a weight and balance system approved in
the operations specifications of the certificate holder. For
additional information on approved weight and balance
control programs for operations under parts 121 and 135,
reference the current edition of AC 120-27, Aircraft Weight
and Balance Control. AC 43.13-l, Acceptable Methods,
Techniques and Practices—Aircraft Inspection and Repair
also requires that the aircraft mechanic ensure that the weight
and balance data in the aircraft records is current and accurate
after a 100-hour or annual inspection.
Terms and Definitions
The pilot should be familiar with the appropriate terms
regarding 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 specifications.
• 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 r to
indicate a change of values. As an example, rCG
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
manufacturer.
• 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 is normally allowed to have at landing.
• Maximum ramp weight—the total weight of a loaded
aircraft including all fuel. It is greater than the takeoff
weight due to the fuel that will be burned during the
taxi and run-up 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 fixed
ballast, hydraulic fluid, unusable fuel, and full engine
oil.
• 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.
Principles of Weight and Balance Computations
It is imperative that all pilots understand the basic principles
of weight and balance determination. The following methods
of computation can be applied to any object or vehicle for
which weight and balance information is essential.
By determining the weight of the empty aircraft and adding
the weight of everything loaded on the aircraft, a total weight
can be determined—a simple concept. A greater problem,
particularly if the basic principles of weight and balance are
not understood, is distributing this weight in such a manner
that the entire mass of the loaded aircraft is balanced around
a point (CG) that must be located within specified limits.
The point at which an aircraft balances can be determined by
locating the CG, which is, as stated in the definitions of terms,
100
lb
50
lb
50
lb
25"
50"
100"
2,500
in-lb
2,500
in-lb
5,000
in-lb
Fulcrum
Datum
100 x 25 = 2,500
50 x 50 = 2,500
Total = 5,000
Wt x Arm = Moment
(lb) x (in) = (in-lb)
Figure 10-4. Establishing a balance.
50
lb
100"
Moment = 5,000 in-lb
Fulcrum
Datum
Wt x Arm = Moment
(lb) x (in) = (in-lb)
50 x 100 = 5,000Note: The datum is assumed to be
located at the fulcrum.
Figure 10-3. Determining moment.
Aft limit
Fwd limit
Datum
CG
range
( + )
Arm
( – )
Arm
( + ) Arm 70"
Moment = 700 in-lb
Sta 0 Sta 70
10 lb
Figure 10-2. Weight and balance.
the imaginary point at which all the weight is concentrated.
To provide the necessary balance between longitudinal
stability and elevator control, the CG is usually located
slightly forward of the center of lift. This loading condition
causes a nose-down tendency in flight, which is desirable
during flight at a high AOA and slow speeds.
As mentioned earlier, a safe zone within which the balance
point (CG) must fall is called the CG range. The extremities
of the range are called the forward CG limits and aft CG
limits. These limits are usually specified in inches, along the
longitudinal axis of the airplane, measured from a reference
point called a datum reference. The datum is an arbitrary
point, established by aircraft designers that may vary in
location between different aircraft. [Figure 10-2]
The distance from the datum to any component part or any
object loaded on the aircraft is called the arm. When the
object or component is located aft of the datum, it is measured
in positive inches; if located forward of the datum, it is
measured as negative inches or minus inches. The location
of the object or part is often referred to as the station. If
the weight of any object or component is multiplied by the
distance from the datum (arm), the product is the moment.
The moment is the measurement of the gravitational force
that causes a tendency of the weight to rotate about a point
or axis and is expressed in inch-pounds (in-lb).
To illustrate, assume a weight of 50 pounds is placed on
the board at a station or point 100 inches from the datum.
The downward force of the weight can be determined by
multiplying 50 pounds by 100 inches, which produces a
moment of 5,000 in-lb. [Figure 10-3]
To establish a balance, a total of 5,000 in-lb must be applied
to the other end of the board. Any combination of weight
and distance which, when multiplied, produces a 5,000 in-
lb moment will balance the board. For example (illustrated
in Figure 10-4), if a 100-pound weight is placed at a point
(station) 25 inches from the datum, and another 50-pound
weight is placed at a point (station) 50 inches from the datum,
the sum of the product of the two weights and their distances
total a moment of 5,000 in-lb, which will balance the board.
Weight and Balance Restrictions
An aircraft’s weight and balance restrictions should be
closely followed. The loading conditions and empty weight
of a particular aircraft may differ from that found in the
AFM/POH because modifications or equipment changes
may have been made. Sample loading problems in the
AFM/POH are intended for guidance only; therefore, each
aircraft must be treated separately. Although an aircraft is
certified for a specified maximum gross takeoff weight, it
may not safely take off at this weight under all conditions.
Conditions that affect takeoff and climb performance, such as
high elevations, high temperatures, and high humidity (high
density altitudes), may require a reduction in weight before
flight is attempted. Other factors to consider when computing