Par 7-148 Page 7-324 TABLE 7-5. Straight-shank terminal dimensions. (Cross reference AN to MS: AN-666 to MS 21259, AN-667 to MS 20667, AN-668 to MS 20668, AN-669 to MS 21260.)
Before swaging After swaging
Cable size (inches)
Wire strands
Outside diameter
Bore diameter
Bore length
Swaging length Minimum breaking strength (pounds)
Shank diameter * 1/16 3/32 1/8 5/32 3/16 7/32 1/4 9/32 5/16 3/8 7 x 7 7 x 7 7 x 19 7 x 19 7 x 19 7 x 19 7 x 19 7 x 19 7 x 19 7 x 19
0.160 .218 .250 .297 .359 .427 .494 .563 .635 .703
0.078 .109 .141 .172 .203 .234 .265 .297 .328 .390
1.042
1.261
1.511
1.761
2.011
2.261
2.511
2.761
3.011
3.510
0.969
1.188
1.438
1.688
1.938
2.188
2.438
2.688
2.938
3.438 480 920 2,000 2,800 4,200 5,600 7,000 8,000 9,800 14,400
0.138 .190 .219 .250 .313 .375 .438 .500 .563 .625 *Use gauges in kit for checking diameters.
NOTE: If the terminal is drilled completely through, push the cable into the terminal until it reaches the approximate position shown in figure 7-10. If the hole is not drilled through, insert the cable until the end rests against the bottom of the hole.
FIGURE 7-10. Insertion of cable into terminal.
Accomplish the swaging operation in accordance with the instructions furnished by the manufacturer of the swaging equipment.
Inspect the terminal after swaging to determine that it is free from the die marks and splits, and is not out-of-round. Check for cable slippage in the terminal and for cut or broken wire strands.
Using a “go no-go” gauge or a micrometer, check the terminal shank diameter as shown in figure 7-11 and table 7-5.
FIGURE 7-11. Gauging terminal shank after swaging.
Test the cable by proof-loading it to 60 percent of its rated breaking strength.
Splicing. Completely severed cables, or those badly damaged in a localized area, may be repaired by the use of an eye
Par 7-148 Page 7-325 terminal bolted to a clevis terminal. (See figure 7-12(a).) However, this type of splice can only be used in free lengths of cable which do not pass over pulleys or through fair-leads.
FIGURE 7-12. Typical cable splices.
Swaged ball terminals. On some aircraft cables, swaged ball terminals are used for attaching cables to quadrants and special connections where space is limited. Single shank terminals are generally used at the cable ends, and double shank fittings may be used at either the end or in the center of the cable. Dies are supplied with the swaging machines for attaching these terminals to cables by the following method.
The steel balls and shanks have a hole through the center, and are slipped over the cable and positioned in the desired location.
Perform the swaging operation in accordance with the instructions furnished by the manufacturer of the swaging equipment.
Check the swaged fitting with a “go no-go” gauge to see that the fitting is properly compressed, and inspect the physical condition of the finished terminal. (See figure 7-13.)
FIGURE 7-13. Typical terminal gauge.
Cable slippage in terminal. Ensure that the cable is properly inserted in the terminal after the swaging operation is completed.
Instances have been noted wherein only 1/4 inch of the cable was swaged in the terminal. Observance of the following precautions should minimize this possibility.
Measure the length of the terminal end of the fitting to determine the proper length of cable to be inserted into the barrel of the fitting.
Lay off this length at the end of the cable and mark with masking tape. Since the tape will not slip, it will provide a positive marking during the swaging process.
After swaging, check the tape marker to make certain that the cable did not slip during the swaging operation.
Remove the tape and paint the junction of the swaged fitting and cable with red tape.
At all subsequent service inspections of the swaged fitting, check for a gap in the painted section to see if cable slippage has occurred.
Nicopress Process. A patented process using copper sleeves may be used up to the full rated strength of the cable when the cable is looped around a thimble. This process may also be used in place of the five-tuck splice on
Par 7-148 Page 7-326 cables up to and including 3/8 inch diameter. The use of sleeves that are fabricat ed of materials other than copper will require engineering approval for the specific application by the FAA.
Before undertaking a nicopress splice, determine the proper tool and sleeve for the cable to be used. Refer to table 7-6 and table 7-7 for details on sleeves, tools, and the number of presses required for the various sizes of aircraft cable. The tool must be in good working condition and properly adjusted to ensure a satisfactory splice.
To compress a sleeve, have it well-centered in the tool groove with the major axis of the sleeve at right angles to the tool. If the sleeve appears to be out of line after the press is started, open the tool, re-center the sleeve, and complete the press.
Thimble-Eye Splice. Before undertaking a thimble-eye splice, initially position the cable so the end will extend slightly beyond the sleeve, as the sleeve will elongate somewhat when it is compressed. If the cable end is inside the sleeve, the sp lice may not hold the full strength of the cable. It is desirable that the oval sleeve be placed in close proximity to the thimble points, so that when compressed, the sleeve will contact the thimble as shown in figure 7-14. The sharp ends of the thimble may be cut off before being used; however, make certain the thimble is firmly secured in the cable loop after the splice has been completed. When using a sleeve requiring three compressions, make the center compression first, the compression next to the thimble second, and the one farthest from the thimble last.
Lap Splice. Lap or running splices may also be made with copper oval sleeves. When making such splices, it is usually necessary to use two sleeves to develop the full
FIGURE 7-14. Typical thimble-eye splice.
strength of the cable. The sleeves should be positioned as shown in figure 7-12(b), and the compressions made in the order shown. As in the case of eye splices, it is desirable to have the cable ends extend beyond the sleeves sufficiently to allow for the increased length of the compressed sleeves.
Stop Sleeves. Stop sleeves may be used for special cable end and intermediate fittings. They are installed in the same manner as nicopress oval sleeves.
NOTE: All stop sleeves are plain copper.
Certain sizes are colored for identification.
Terminal Gauge. To make a satisfactory copper sleeve installation, it is important that the amount of sleeve pressure be kept uniform. The completed sleeves should be checked periodically with the proper gauge.
Hold the gauge so that it contacts the major axis of the sleeve. The compressed portion at the center of the sleeve should enter the gauge opening with very little clearance, as shown in figure 7-15. If it does not, the tool must be adjusted accordingly.
Other Applications. The preceding information regarding copper oval sleeves and stop sleeves is based on tests made with flexible aircraft cable. The sleeves may also be
Par 7-148 Page 7-327 TABLE 7-6. Copper oval sleeve data.
Copper oval sleeve stock No.
Cable size
Plain
Plated*
Manual tool No.
Sleeve length before compression (approx.)
(inches) Sleeve length after compression (approx.)
(inches)
Number of presses
Tested strength (pounds)
3/64 18-11-B4 28-11-B4 51-B4-887 3/8 7/16 1 340 1/16 18-1-C 28-1-C 51-C-887 3/8 7/16 1 550 3/32 18-2-G 28-2-G 51-G-887 7/16 1/2 1 1,180 1/8 18-3-M 28-3-M 51-M-850 9/16 3/4 3 2,300 5/32 18-4-P 28-4-P 51-P-850 5/8 7/8 3 3,050 3/16 18-6-X 28-6-X 51-X-850 1 1 1/4 4 4,350 7/32 18-8-F2 28-8-F2 51-F2-850 7/8 1 1/16 4 5,790 1/4 18-10-F6 28-10-F6 3-F6-950 1 1/8 1 1/2 3 7,180 5/16 18-13-G9 28-13-G9 3-G9-950 1 1/4 1 5/8 3 11,130 No. 635 Hydraulic tool dies
3/8 18-23-H5 28-23-H5 Oval H5 1 1/2 1 7/8 1 16,800 7/16 18-24-J8 28-24-J8 Oval J8 1 3/4 2 1/8 2 19,700 1/2 18-25-K8 28-25-K8 Oval K8 1 7/8 2 1/2 2 25,200 9/16 18-27-M1 28-27-M1 Oval M1 2 2 5/8 3 31,025 5/8 18-28-N5 28-28-N5 Oval N5 2 3/8 3 1/8 3 39,200 *Required on stainless cables due to electrolysis caused by different types of metals.
TABLE 7-7. Copper stop sleeve data.
Cable size (inch) Sleeve No. Tool No . Sleeve Sleeve Tested strength (pounds) 3/64 871-12-B4 51-B4-887 7/32 11/64 280 1/16 871-1-C 51-C-887 7/32 13/64 525 3/32 871-17-J (Yellow) 51-MJ 5/16 21/64 600 1/8 S71-18-J (Red) 51-MJ 5/16 21/64 800 5/32 871-19-M 51-MJ 5/16 27/64 1,200 3/16 871-20-M (Black) 51-MJ 5/16 27/64 1,600 7/32 871-22-M 51-MJ 5/8 7/16 2,300 1/4 871-23-F6 3-F6-950 11/16 21/32 3,500 5/16 871-26-F6 3-F6-950 11/16 21/32 3,800 NOTE: All stop sleeves are plain copper. Certain sizes are colored for identification.
used on wire ropes of ot her construction, if each specific type of cable is proof-tested initially. Because of variation in rope strengt hs, grades, construction, and actual diameters, the test is necessary to insure proper selection of materials, the correct pressing procedure, and an adequate margin of safety for the intended use.
FIGURE 7-15. Typical terminal gauge.
Par 7-149 Page 7-328 CABLE SYSTEM INSPECTION. Aircraft cable systems are subject to a variety of environmental conditions and deterioration.
Wire or strand breakage is easy to visually recognize. Other kinds of deterioration such as wear, corrosion, and/or distortion are not easily seen; therefore, control cables should be removed periodically for a more detailed inspection.
At each annual or 100 hour inspection, all control cables must be inspected for broken wires strands. Any cable assembly that has one broken wire strand located in a critical fatigue area must be replaced.
A critical fatigue area is defined as the working length of a cable where the cable runs over, under, or around a pulley, sleeve, or through a fair-lead; or any section where the cable is flexed, rubbed, or worked in any manner; or any point within 1 foot of a swaged-on fitting.
A swaged-on fitting can be an eye, fork, ball, ball and shank, ball and double shank, threaded stud, threaded stud and turnbuckle, compression sleeve, or any hardware used as a termination or end fitting on the cable. These fittings may be attached by various swaging methods such as rotary swaging, roll swaging, hydraulic pressing, and hand swaging tools. (See MIL-T-781.) The pressures exerted on the fittings during the swaging process sometimes pinch the small wires in the cable. This can cause premature failure of the pinched wires, resulting in broken wires.
Close inspection in these critical fatigue areas, must be made by passing a cloth over the area to snag on broken wires. This will clean the cable for a visual inspection, and detect broken wires if the cloth snags on the cable. Also, a very careful visual inspection must be made since a broken wire will not always protrude or stick out, but may lie in the strand and remain in the position of the helix as it was manufactured. Broken wires of this type may show up as a hairline crack in the wire. If a broken wire of this type is suspected, further inspection with a magnifying glass of 7 power or greater, is recommended.
Figure 7-16 shows a cable with broken wires that was not detected by wiping, but was found during a visual inspection. The damage b ecame readily apparent when the cable was removed and bent as shown in figure 7-16.
FIGURE 7-16. Cable inspection technique.
Kinking of wire cable can be avoided if properly handled and installed. Kinking is caused by the cable taking a spiral shape as the result of unnatural twist.
One of the most common causes for this twist is improper unreeling and uncoiling. In a kinked cable, strands and wires are out of position, which creates unequal tension and brings excessive wear at this part of the cable. Even though the kink may be straightened so that the damage appears to be slight, the relative adjustment between the strands has been disturbed so that the cable cannot give maximum service and should be replaced. Inspect cables for a popped core or loose strands. Replace any cable that has a popped core or loose strands regardless of wear or broken wires.
Par 7-149 Page 7-329 Nylon-jacketed cable with any cracks or necking down in the diameter of the jacket shall be replaced. Usable cable life is over when these conditions begin to appear in the nylon jacket.
External wear patterns will extend along the cable equal to the distance the cab le moves at that location and may occur on one side of the cable or on its entire circumference. Replace flex ible and nonflexible cables when the individual wires in each strand appear to blend together (outer wires worn 40 to 50 percent) as depicted in figure 7-17. Actual instances of cable wear beyond the recommended replacement point are shown in figure 7-18.
FIGURE 7-17. Cable wear patterns.
As wear is taking place on the exterior surface of a cable, the same condition is taking place internally, particularly in the sections of the cable which pass over pulleys and quadrants. This condition (shown in figure 7-19) is not easily detected unless the strands of the cable are separated. This type of wear is a result of the relative motion between inner wire surfaces. Under certain conditions, the rate of this type of wear can be greater than that occurring on the surface.
FIGURE 7-18. Worn cable (replacement necessary).
Areas especially conducive to cable corrosion are battery compartments, lavatories, wheel wells, etc.;
where a concentration of corrosive fumes, vapors, and liquids can accumulate. Ca refully examine any cable for corrosion, when it has a broken wire in a section that is not in contact with a wear-producing airframe component, such as a pulley, fair-lead, etc. If the surface of the cable is corroded, relieve cable tension and carefully force the cable open by reverse twisting and visually inspect the interior. Corrosion on the interior strands of the cable constitutes failure, and the cable must be replaced. If no internal corrosion is detected, remove loose extern al rust and corrosion with a clean, dry, coarse-weave rag, or fiber brush. Do not use metallic
Par 7-149 Page 7-330
FIGURE 7-19. Internal cable wear.
wool or solvents to clean installed cables. Use of metallic wool will embed dissimilar metal particles in the cables and create further corrosion problems. Solvents will remove internal cable lubricant allowing cable strands to abrade and further corrode. After thorough cleaning, sparingly apply specification MIL-C-16173, grade 4, corrosion-preventive compound to cable. Do not apply the material so thick that it will interfere with the operation of cables at fair-leads, pulleys, or grooved bellcrank areas.
Examine cable runs for incorrect routing, fraying, twisting, or wear at fair-leads, pulleys, antiabrasion strips, and guards. Look for interference with adjacent structure, equipment, wiring, plumbing, and other controls. Inspect cable syst ems for binding, full travel, and security of attaching ha rdware. Check for slack in the cable system by attempting to move the control column and/or pedals while the gust locks are installed on the control surfaces. With the gust locks removed, actuate the controls and check for friction or hard movement.
These are indications that excessive cable tension exists.
NOTE: If the control movement is stiff after maintenance is performed on control surfaces, check for parallel cables twisted around each other, or cables connected in reverse.
Check swaged terminal reference marks for an indication of cable slippage within the fitting. Inspect the fitting assembly for distortion and/or broken strands at the terminal. Ensure th at all bearings and swivel fittings (bolted or pinned) pivot freely to prevent binding and subsequent failure . Check turnbuckles for proper thread exposure and broken or missing safety wires/clips.
Inspect pulleys for roughness, sharp edges, and presence of foreign material embedded in the grooves.
Examine pulley bearings to ensure proper lubrication, smooth rotation; and freedom from flat spots, dirt, and paint spray. During the inspection, rotate the pulleys, which only turn through a small arc, to provide a new bearing surface for the cab le. Maintain pulley alignment to prevent the cable from riding on the flanges and chafing against guards, covers, or adjacent structure. Check all pu lley brackets and guards for damage, alignment, and security.
Various cable system malfunctions may be detected by analyzing pulley conditions. These include such discrepancies as too much tension, misalignment, pulley bearing problems, and size mismatches between cables and pulleys. Examples of these condition are shown in figure 7-20.
Par 7-149 Page 7-331
FIGURE 7-20. Pulley wear patterns.
Inspect fair-leads for wear, breakage, alignment, cleanliness, and security. Examine cable routing at fairleads to ensure that defecti on angles are no greater than 3° maximum. Determine that all guides and antiabrasion strips are secure and in good condition.
Examine pressure seals for wear and/or material deterioration. Seal guards should be positioned to prevent jamming of a pulley in case pressure seal fails and pieces slide along the cable.
CORROSION AND RUST PRE-VENTION. To ensure a satisfactory service life for aircraft control cables, use a cable lubricant to reduce internal friction and prevent corrosion.
If the cable is made from tinned steel, coat the cable with rust-preventive oil, and wipe off any excess. It should be noted that corrosionresistant steel cable does not require this treatment for rust prevention.
Lubrication and corrosion pre-ventive treatment of carbon steel cables may be effected simultaneously by application of compound MIL-C-16173, grade 4, or MIL-C-11796, Class I. MIL-C-16173 compound should be brushed, sprayed, or wiped on the cable to the extent it penetrates into the strands and adequately covers the cable surfaces. It will dry “tack free” in 24 hours at 77 °F. MIL-C-11796 compound is applied by dipping the cable for 1/2 minute into a tank of compound heated to 77 ° ± 5 °C (170 ° ± 9 °F) for 1/2 minute then removing it and wiping off the excess oil. (An example of cable corrosion, attributable to battery acid, is shown in figure 7-21.)
Par 7-150 Page 7-332 (and 7-40)
FIGURE 7-21. Corrosion.
WIRE SPLICES. Standard manufacturing splices have been mistaken for defects in the cable because individual wire end splices were visible after assembly of a finished cable length. In some instances, the process of twisting outer strands around the core strand may also slightly flatten individual outer wires, particularly in the area of a wire splice. This flattening is the result of die-sizing the cable, and does not affect the strength of the cable.
These conditions (as shown in figure 7-22) are normal, and are not a cause for cable rejection.
FIGURE 7-22. Manufacturer’s wire splice.
CABLE MAINTENANCE. Frequent inspections and preservation measures such as rustprevention treatments for bare carbon steel cable areas, will help to extend cable service life. Where cables pass through fair-leads, pressure seals, or over pulleys, remove accumulated heavy coatings of corrosionprevention compound. Provide corrosion protection for these cable sections by lubricating with a light coat of grease or general-purpose, low-temperature oil.
CABLE TENSION ADJUST-MENT. Carefully adjust, control cable tension in accordance with the airframe manufacturer’s recommendations. On large aircraft, take the temperature of the immediate area into consideration when using a tension meter. For long cable sections, use the average of two or three temperature readings to obtain accurate tension values. If necessary, compensate for extreme surface temperature variations that may be encountered if the aircraft is operated primarily in unusual geographic or climatic conditions such as arctic, arid, or tropic locations. Use rigging pins and gust locks, as necessary, to ensure satisfactory results. At the completion of rigging operations, check turnbuckle adjustment and safetying in accordance with section 10 of this chapter.
7-154.7-164. [RESERVED.]
Par 7-165 Page 7-333 (and 7-42)
SECTION 9. TURNBUCKLES
GENERAL. A turnbuckle is a device used in cable systems to provide a means of adjusting tension. Turnbuckles have barrel-shaped sleeves with internal left- and right-hand threads at opposite ends. The cables, with terminals attached, are made to such a length that, when the turnbuckle is adjusted to give the specified cable tension, a sufficient number of threads on the terminal ends are screwed into the barrel to hold the load. The cliplocking turnbuckle and its associated parts are identical to standard AN and MS parts except for a slot grooved on the interior of the barrel and the shanks of the forks, eyes, etc. The clip-locking turnbuckle parts have the following drawing numbers: MS21251, turnbuckle body;
MS21252, turnbuckle clevis end; MS21253, turnbuckle clevis end (for bearing); NAS649 and NAS651, turnbuckle clip; MS21254 and NAS648, turnbuckle eye (for pin); MS21255 and NAS647, turnbuckle eye end (for wire rope);
NAS645 and NAS646, turnbuckle fork;
MS21256, turnbuckle barrel locking clip;
AN130-170, turnbuckle assemblies; and, MS21259 and MS21260, terminal, wire rope, stud.
NOTE: Turnbuckles showing signs of thread distortion/bending should be replaced.
Turnbuckle ends are designed for providing the specified cable tension on a cable system, and a bent turnbuckle would place undesirable stress on the cable, impairing the function of the turnbuckle.
TURNBUCKLE INSTALLATION. (See figure 7-23.) When installing cable system turnbuckles, it is necessary to screw both threaded terminals into the turnbuckle barrel an equal amount. It is essential that turnbuckle terminals be screwed into the barrel so that not more than three threads on the terminal are exposed. (See figure 7-23A.) On initial installation, the turnbuckle terminals should not be screwed inside the turnbuckle barrel more than four threads. (See figure 7-23B.)
FIGURE 7-23. Turnbuckle thread tolerance.
WITNESS HOLE. Some manufacturers of turnbuckles incorporate a “witness hole,” in the turnbuckle barrel to ensure that the threaded cable terminals are screwed in far enough into the barrel. The “witness hole” can be inspected visually, or by using a piece of safety wire as a probe.
7-168.7-178. [RESERVED.]
Par 7-179 Page 7-334
SECTION 10. SAFETY METHODS FOR TURNBUCKLES
GENERAL. Safety all turnbuckles with safety wire using either the double or single-wrap method, or with any appropriately approved special safetying device complying with the requirements of FAA Technical Standard Order TSO-C21. The swaged and unswaged turnbuckle assemblies are covered by AN standard drawings. Do not reuse safety wire.
Adjust the turnbuckle to the correct cable tension so that no more than three cable threads are exposed on either side of the turnbuckle barrel.
DOUBLE-WRAP METHOD. Of the methods using safety wire for safetying turnbuckles, the method described here is preferred, although either of the other methods described is satisfactory. The method of double-wrap safetying is shown in figure 7-24(A).
Use two separate lengths of wire. Run one end of the wire through the hole in the barrel of the turnbuckle and bend the ends of the wire toward opposite ends of the turnbuckle.
Pass the second length of the wire into the hole in the barrel and bend the ends along the barrel on the side opposite the first. Spiral the two wires in opposite directions around the barrel to cross each other twice between the center hole and the ends.
Then pass the wires at the end of the turnbuckle in opposite directions through the hole in the turnbuckle eyes or between the jaws of the turnbuckle fork, as applicable, laying one wire along the barrel and wrapping the other at least four times around the shank of the turnbuckle and bindi ng the laid wires in place before cutting the wrapped wire off.
Wrap the remaining length of safety wire at least four turns around the shank and cut it off. Repeat the procedure at the opposite end of the turnbuckle.
When a swaged terminal is being safetied, pass the ends of both wires through the hole provided in the terminal for this purpose and wrap both ends around the shank as previously described. If the hole is not large enough to allow passage of both wires, pass the wire through the hole and loop it over the free end of the other wire, and then wrap both ends around the shank as previously described. Another satisfactory double-wrap method is similar to the previous method, except that the spiraling of the wires is omitted as shown in figure 7-24(B).
SINGLE-WRAP METHOD. The single-wrap methods described in the following paragraphs and as illustrated in figure 7-24(C) and (D) are acceptable, but are not the equal of the doublewrap methods.
Pass a single length of wire through the cable eye or fork, or through the hole in the swaged terminal at either end of the turnbuckle assembly. Spiral each of the wire ends in opposite directions around the first half of the turnbuckle barrel, so as to cross each other twice.
Thread both wire ends through the hole in the middle of the barrel so that the third crossing of wire ends is in the hole, again, spiral the two wire ends in opposite directions around the remaining half of the turnbuckle, crossing them twice. Then, pass one wire end through the cable eye or fork, or through the hole in the swaged terminals, in the manner previously described. Wrap both wire ends around the shank for at least four turns each, cutting off excess wire. This method is shown in figure 7-24(C).
Par 7-179 Page 7-335
F IGURE 7-24. Safetying turnbuckles.
For the method shown in figure 7-24D, pass one length of wire through the center hole of the turnbuckle and bend the wire ends toward opposite ends of the turnbuckle. Then pass each wire end through the cable eye or fork, or through the hole in the swaged terminal, and wrap each wire around the shank for at least four turns, cutting off excess wire. After safetying, no more than three threads of the turnbuckle threaded terminal should be exposed.
SAFETY-WIRE SECURED TURNBUCKLES. (See figure 7-25.) Before securing turnbuckles, threaded terminals should be screwed into the turnbuckle barrel until no more than three threads of either terminal are outside the barrel. After the turnbuckle has been adjusted for proper cable tension, two pieces of safety wire are inserted, half the wire length into the hole in the center of the turnbuckle barrel. The safety-wires are bent so that each wire extends half the length of the turnbuckle on top and half on bottom. The ends of the wires are passed through the hole in the turnbuckle eyes or between the jaws of the turnbuckle fork, as applicable. The wires are then bent toward the center of the turnbuckle and each wire is wrapped around the shank four times, binding the wrapping wires in place as shown in figure 7-25.
When a swaged terminal is being secured, one wire is passed through the hole in the terminal and is looped over the free end of the other wire and both ends wrapped around the shank. All lock wire used in the safetying of turnbuckles should be carbon steel, corrosion-resistant steel, ni ckel-chromium iron alloy (inconel), nickel-copper alloy (monel) or aluminum