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aircraft chosen to be weighed are those having the highest
time since last weighing.
Weighing to reestablish fleet weights is normally conducted
on a 3-year basis unless changes in aircraft configuration
make it necessary to reweigh and/or recalculate the CG sooner
than called for by this schedule.
Weighing Procedures
Required operating practices must be followed when
weighing large aircraft. Check the aircraft to be sure all the
required equipment items are installed and all the fluids are
properly accounted for. The aircraft must be clean, and the
weighing must be done in an enclosed building.
Large aircraft are not usually raised off the floor on jacks for
weighing. Rather, they are weighed on ramp-type scales
similar to those in Figure 3-2 on Page 3-2. The scales must
be properly calibrated, zeroed, and used in accordance with
the manufacturer’s instructions. Each scale should be
periodically checked for accuracy as recommended in the
manufacturer’s calibration schedule either by the manufacturer,
or by a recognized facility such as a civil department
of weights and measures. If no manufacturer’s schedule is
available, the period between calibrations should not exceed
1 year.
For Large Aircraft
Weight and balance control consists of:
• Establishing and monitoring the empty weight and EWCG.
• Maintaining a loading schedule to keep the weight and CG
within limits.
• Providing information to the flight crew that allows them to load
the aircraft in such a way that the maximum payload may be
safely carried.
6– 3
Determine the location of the CG in inches aft of the datum
by using this formula:
Basic operating index: The
moment of the airplane at its basic
operating weight divided by the
appropriate reduction factor.
PAX: Passengers.
Figure 6-1. Loading tables.
Determining the Loaded CG of the
Airplane in Percent MAC
It is the responsibility of the flight crew to know that both
the weight of the airplane and the location of the CG are
within the allowable limits for both takeoff and landing.
The basic operating weight (BOW) and the basic operating
index are entered into a loading schedule like the one in
Figure 6-1 and the variables for the specific flight are entered
as are appropriate to determine the loaded weight and CG.
Use the data in this example:
Basic operating weight (BOW) ......................... 105,500 lbs
Basic operating index (total moment/1,000) ......... 92,837.0
MAC .......................................................................... 180.9 in
LEMAC ........................................................................ 860.5
Determine the distance from the CG to the LEMAC by
subtracting the distance between the datum and LEMAC from
the distance between the datum and the CG:
The location of the CG in percent of MAC must be known in
order to set the stabilizer trim for takeoff. Use this formula:
On Board Aircraft Weighing System
Some large transport airplanes have an on board aircraft
weighing system (OBAWS) that, when the aircraft is on the
ground, gives the flight crew a continuous indication of the
aircraft gross weight and the location of the CG in % MAC.
The system consists of strain sensing transducers in each
main wheel and nose wheel axle, a weight and balance
computer, and indicators that show the gross weight, the CG
location in % MAC, and an indicator of the ground attitude
of the aircraft.
The strain sensors measure the amount each axle deflects
and send this data into the computer, where signals from all
of the transducers and the ground attitude sensor are
integrated. The results are displayed on the indicators for the
flight crew.
Strain sensor: A device that
converts a physical phenomenon into
an electrical signal. Strain sensors in
a wheel axle sense the amount the
axle deflects and create an electrical
signal proportional to the force that
caused the deflection.
Use Figure 6-2 to determine the moment indexes for the
passengers (PAX), cargo, and fuel.
The airplane is loaded in this way:
Passengers (nominal weight 170 pounds each)
Forward compartment ............................................... 18
Aft compartment ........................................................ 95
Cargo
Forward hold ................................................... 1,500 lbs
Aft hold ........................................................... 2,500 lbs
Fuel
Tanks 1 & 3 ........................................... 10,500 lbs each
Tank 2 ............................................................ 28,000 lbs
　
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