(b)
Calculate the gross weight from the scales and write the data in Figure 514, in the SCALES column and the SAMPLE 3 row.
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(9)
Push the RESET key to stop WBC mode 01. (The WBC shows PROCESS ABORTED.)
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(10)
In each of the columns of data in Figure 514, calculate the average of the three samples and write the result in the AVERAGE row.
WBC MODE 01 SCALES
SAMPLE GROSS WEIGHT CG GROSS WEIGHT CG
(lbs) (%MAC) (lbs) (%MAC)
SAMPLE 1 SAMPLE 2 SAMPLE 3
AVERAGE [1] [2] [3] [4]
[5]
P = PITCH ANGLE (`) =
ANGLE CORRECTION = 55tanP =
[6]
ADJUSTED CG (%MAC) = SCALES CG - ANGLE CORRECTION =
Calibration Check - Gross Weight and Center of Gravity (CG) Comparison
Figure 514
E81077
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(11) Calculate the scale CG using the following equation and write the result in the scales, CG (box 4).
C.G. (%MAC) = [(TOTAL MOMENT / TOTAL G.W.) - 1258.0] / 3.278
Where TOTAL MOMENT =
[ (Wheel 1 + Wheel 2 + Wheel 13 + Wheel 14 ) 1313.5 ]
+[ (Wheel 3 + Wheel 4 + Wheel 15 + Wheel 16 ) 1371.5 ]
+[ (Wheel 5 + Wheel 6 + Wheel 9 + Wheel 10 ) 1434.5 ]
+[ (Wheel 7 + Wheel 8 + Wheel 11 + Wheel 12 ) 1492.5 ]
+[ (Wheel 17 + Wheel 18 ) 395.0 ]
and TOTAL G.W. = The sum of all 18 wheel weights
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(12)
Make sure that the AVERAGE GROSS WEIGHT from WBC MODE 01 (Figure 514, box 1) is between -1% and +1% of the AVERAGE GROSS WEIGHT from the SCALES (box 3).
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(13)
Calculate the adjusted center of gravity (CG):
(a) Measure the value of P, where P is the airplane longitudinal pitch angle (pitch attitude), in degrees (nose-up attitude is positive in sign). Use a plumb bob or use CMCS input monitoring to find the pitch attitude of the airplane. Write the result in Fig. 514, P=PITCH ANGLE (°). 1) Do this to use a plumb bob:
a) Hang a plumb bob in the wheel well of the right body gear and read the pitch attitude (AMM 08-00-00/201).
2) Do this to use input monitoring to find the pitch attitude: a) Make sure the IRS is in the NAV mode. b) Select OTHER FUNCTIONS from page 2 of the CMC MENU. c) Select INPUT MONITORING from the other functions menu. d) Use the CDU keypad to type this: E/80/324/00 e) Push the top left key on the CDU to start input
monitoring.
NOTE:____Three samples show on the display. Each sample is two lines of 1's and 0's. Bit 32 is the left bit of the first line. Bit 1 is the right bit of the second line.
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747-400 MAINTENANCE MANUAL
f) Make a record of bits 29 through 15.
NOTE: Bit 29 is the sign bit; 0 is + (positive), 1
____ is - (negative). Bits 28 through 15 are the data bits. Bit 28 is the most significant bit.
g) Do this to convert the binary to decimal value:
NOTE: The result should be between -5 and +5 degrees.
____
1 If bit 29 is 0 (positive), convert bits 28 through
_ 15 from binary to decimal and multiply by .011 to get the pitch attitude.
2 If bit 29 is 1 (negative), take the two's complement
_ of bits 28 through 15, convert bits 28 through 15 from binary to decimal and multiply by .011 to get the pitch attitude.
(b) Multiply 55 times the tangent of P to calculate the ANGLE CORRECTION (box 5).
NOTE: ANGLE CORRECTION = 55tan(P)
____
(c) Subtract the ANGLE CORRECTION (box 5) from the SCALES CG (box 4) to calculate the ADJUSTED CG (box 6).
NOTE: ADJUSTED CG = SCALES CG - ANGLE CORRECTION
____
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(14) Make sure that the AVERAGE CG from WBC MODE 01 (box 2) is between -1% and +1% of the ADJUSTED CG from the SCALES (box 6).
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