3-10-3
WHEN YOU USE PNEUMATIC BAGS AND TETHERS Page 3-8 Jul 01/2005
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3-10-4 When You Use Moveable Cranes and Slings with Tethers
1.
Get an approved crane person to do a test of the load prior to the final airplane lifting. This person adjusts the crane until you can operate it safely. When you start lifting the low part of an airplane this will result in an inward movement of the lift point and shift of CG. This is not a stable condition. In this situation the airplane CG continues to change during the full operation.
2.
For these operations you must use tethers at those points on the airplane that will help you make the operation stable and maintain a controlled lift.
3-10-4
WHEN YOU USE MOVEABLE CRANES AND SLINGS WITH TETHERS Page 3-9 Jul 01/2005
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3-20 TETHERS (STABILIZE THE AIRPLANE) 3-20-1 Configurations for Tethers
1. General
A. We show the recommended tether configurations for the 757 airplane in this section. You can make the airplane stable with a small number of correctly installed lines. It can be necessary to use more lines to prevent damage to the airplane from a sudden load. This load can be a wind load or the load from an attitude change during the movement of the airplane. Once you are at the site and determine the terrain and recovery procedures to be used, a decision about the number and position of tether lines can be made. Use sufficient lines to make the airplane stable for your airplane condition.
B. Make sure that each tether line has an equal tether line that goes in the opposite direction. Each tether line must have an adjustment device (block and tackle, turnbuckle, hoist, etc) to permit small changes in the length of the line. This adjustment device also changes the load on the line and on the airplane. Make frequent changes to keep a positive load on the lines and to keep them tight. Use a dynamometer on each line. A person must monitor each dynamometer while you move the airplane. This person also makes sure that the loads at the airplane tether point are not too large.
C. Do not make the selection of a tether line diameter until you know the necessary load. Refer to SUBJECT 3-20-2 for additional information on the selection and installation of tether lines. Refer to Figure 3-15 and Figure 3-17 for tethering line attachment hardware.
2. Tether Configurations
A. You can use tethers on this airplane at the locations shown in Figure 3-3 through Figure 3-9.
3-20-1
CONFIGURATIONS FOR TETHERS
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3-20-2 Tether Lines
1.
You must be careful in the selection and the installation of the tether lines. Use a factor of safety that is more than 5. This factor of safety is for the failure strength (breaking strength) of the line. See Figure 3-2 for the failure strength of some different material that you can use for a tether line.
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