can be recapped so that the new tread will give service comparable to the original tread. The recapping and repairing of aircraft tires has been practiced for many years and has saved aircraft operators considerable sums of money.
which might otherwise have been discarded have been safely reconditioned (many repeatedly) for continued service.
Recapping Aircraft Tires Recapping is a general term meaning reconditioning of a tire by renewing the tread, or renewing the tread plus one or both sidewalls. (See figure 9-62.) There are actually four different types of recapping for aircraft tires.
Top Capping--For tires worn to the bottom of the tread design, with no more than slight flat spotting and/or shoulder wear, the old tread is roughened and a new tread is applied.
Full Capping-For tires worn all around, those flat spotted to the cords, or those with numerous cuts in the tread area, the new tread material is wider than that used on a top cap, and comes down over the shoulder of the tire for several Three-Quarter Retread--For tires needing a new tread, plus renewing of the sidewall rubber on one side, due to damage or weather checking, a full cap is applied, and in addition, approximately 16" of the thickness of the old sidewall rubber is buffed off one side. New sidewall rubber is then applied from the bead to the edge of the new tread, on the buffed side only.
Bead-to-Bead Retread-A new tread and both new sidewalls are applied by this method.
Tires That May Be Recapped Tires with sound cord bodies and beads, or which meet injury limitations described under "Repairable Aircraft Tires."
Tires which are worn to 80 percent or more of their total tread depth.
Tires with one or more flat spots severe enough to cause an out-of-balance condition, regardless of the percentage of wear. Tires having so many tread cuts that repairing the tread rubber would be uneconomical.
Nonrecappable Tires Tires having injuries which would make them nonrepairable.
Tires with six full plies or more having any spot worn through more than one body ply. (It is generally not considered economical to retread 4 and 6 ply aircraft tires.)
Tires with weather checking or ozone cracking of tread or sidewall that exposes the cords.
Repairable Aircraft Tires When considering a tire for repairing only, the amount of service remaining in the tire is important. Any tire with at least 30 percent of tread life remaining, normally would be considered as having enough service left in it to warrant repair only.
Nonrepairable Aircraft Tires The following conditions disqualify a tire for repair:
Any injury to the beads, or in the bead area (except injuries limited to the bead cover or finishing strip as previously mentioned under repairable aircraft tires).
A. Sidewall cords damaged beyond B. Sidewall cords OK for retread. C. Worn through breaker only.
repair. OK for retread.
FIGURE 9-62. Operational damage 393
Any tire with protruding bead wire or badly kinked bead.
Any tire which shows evidence of ply or tread separation.
Any tire with loose, damaged, or broken cords on the inside.
Tires with broken or cut cords in the outside of the sidewall or shoulder area.
Tires that have gone fat, or partially flat, due to the melting or failure of fuze plugs in the wheels should normally be scrapped, even though there may be no visible evidence of damage to the inside or outside of the tire. The only exceptions would • use for teased be where it was known that the fuze plug leaked air because of its being defective.
Spot Repairs When considered economical, spot repairs can be made to take care of tread injuries such as cuts, snags, etc., which are through no more than 25 percent of the actual body plies of the tire, and not over 2" in length at the surface. Vulcanized spot repairs are also made at times to fill in tread gouges that do not go deeper than the tread rubber and do not penetrate the cord body.
Low speed tires (under 160 mph) with tread injuries that penetrate no more than 25 percent of the actual body (breaker strips not included), and have a maximum surface length of 2", may be repaired. If the injury penetrates beyond 25 percent of the actual body plies, it may still be repairable but the surface length of the injury should be no more than 1".
High speed tires (over 160 mph) with tread injuries that penetrate no more than 40 percent of the actual body plies (breaker strips and fabric reinforcement strips in the tread not included) and have a maximum surface length of 1½" with maximum width no more than ¼", may be repaired.
Injuries through the cord body in the tread area, measuring ⅛" or less at the largest point, are considered punctures and are easily repaired.
Shallow cuts in the sidewall or shoulder rubber only are repairable if cords are exposed but not damaged.
ing strip, or slight injuries caused by tire tools in the general bead area, are repairable if the injury does not extend into the plies of the tire, and provided there is no sign of separation in the bead area. If the finishing strips are loose or blistered, they can only be replaced by bead-to-bead retreading.
Liner blisters smaller than 4" x 8" may be repaired if there are no more than two in any one quarter section of the tire, and no more than five in the complete tire. Normally, however, it would be more economical to do this repair at the time the tire is recapped.
It is generally considered uneconomical to repair 4- and 6-ply aircraft tires.
OPERATING AND HANDLING TIPS Taxiing Needless tire damage or excessive wear can be prevented by proper handling of the aircraft during taxiing.
Most of the gross weight of any aircraft is on the main landing gear wheels-on two, four, eight or more tires.
to absorb shock of landing and will deflect (bulge at the sidewall) about two and one-half times more than a passenger car or truck tire. The greater deflection causes more working of the tread, produces a scuffing action along the outer edges of the tread and results in more rapid wear.
Also, if an aircraft tire strikes a chuck hole, a stone, or some foreign objects lying on the runway, taxi strip, or ramp, there is more possibility of its being cut, snagged or bruised because of the percentage of deflection. Or, one of the main landing gear wheels, when making a turn, may drop off the edge of the paved surface causing severe sidewall or shoulder damage. The same type of damage may also occur when the wheel rolls back over the edge of the paved surface.
With dual main landing gear wheels, one tire might be forced to take a damaging impact (which two could withstand without damage) simply because all the weight on one side of the plane is concentrated on one tire instead of being divided between two.
As airports grow in size and taxi runs become longer, chances for tire damage and wear increase.
Taxi runs should be no longer than absolutely necessary and should be made at speeds no greater than 25 mph, particularly for aircraft not equipped with nose wheel steering.
For less damage in taxiing, all personnel should see that ramps, parking areas, taxi strips, runways and other paved areas are regularly cleaned and cleared of all objects that might cause tire damage.
Braking and Pivoting Increasing airport traffic, longer taxi runs and longer runs on takeoff and landing are subjecting tires to more abrasion resulting from braking, turning and pivoting.
Severe use of brakes can wear flat spots on tires and cause them to be out of balance, making premature recapping or replacement necessary.
Severe or prolonged application of the brakes can be avoided when ground speed is reduced.
Careful pivoting of aircraft also helps to prolong tire tread life. If an aircraft turned as an automobile or truck does--in a rather wide radiusthe wear on the tire tread would be materially reduced. However, when an aircraft is turned by locking one wheel (or wheels), the tire on the locked wheel is twisted with great force against the pavement. A small piece of rock or stone that would ordinarily cause no damage; can, in such a case, be literally screwed into the tire. This scuffing or grinding action takes off tread rubber and places a very severe strain on the sidewalls and beads of the tire at the same time.
To keep this action at a minimum, it is recommended that whenever a turn is made, the inside wheel (wheels) be allowed to roll on a radius of 20 to 25 feet and up to 40 feet for aircraft with bogies.
Takeoffs and Landings Aircraft tire assemblies are always under severe strain on takeoff or landing. But under normal conditions, with proper control and maintenance of tires, they are able to withstand many such stresses without damage.
Tire damage on takeoff, up to the point of being airborne, is generally the result of running over some foreign object. Flat spots or cuts incurred in pivoting can also be a cause of damage during takeoff or landing.
Tire damage at the time of landing can be traced to errors in judgment or unforeseen circumstances.
Smooth landings result in longer tread wear and eliminate much of the excessive strain on tires at the moment of impact.
Landings with brakes locked, while almost a thing of the past, can result in flat spotting. Removal of the tire for recapping or replacement is almost invariably indicated. Brakes-on landings also cause very severe heat at the point of contact on the tire tread and may even melt the tread rubber (skid burn). Heat has a tendency to weaken the cord body and places severe strain on the beads. In addition, heat buildup in the brakes may literally devulcanize the tire in the bead area.
Under these circumstances, blowouts are not uncommon because air under compression must expand when heated.
On aircraft equipped with tail wheels, a two point landing is usually somewhat smoother than a three point landing, but is ordinarily made at considerably higher speed. As a result, more braking may be required to bring the aircraft to a stop If tires are skidded on the runway at high speed, the action is similar to tires being ground against a fast turning emery wheel.
Sometimes an aircraft will be brought in so fast that full advantage will not be taken of runway length and brakes are applied so severely that flat spots are produced on the tires. Or, if brakes are applied when the plane is still traveling at high speed and still has considerable lift, tires may skid on the runway and become damaged beyond further use or reconditioning.
The same thing may occur during a rough landing if brakes are applied after the first bounce.
For maximum tire service, delay brake application until the plane is definitely settled into its final roll.
More tires fail on takeoff than on landing and such failures on takeoff can be extremely dangerous. For that reason, emphasis must be placed on proper preflight inspection of tires and wheels.
Condition of Landing Field Regardless of the preventive maintenance and extreme care taken by the pilot and ground crew in handling the aircraft, tire damage is almost sure to result if runways, taxi strips, ramps and other paved field areas are in a bad condition or poorly maintained.
Chuck holes, pavement cracks or step-offs from these areas to the ground, all can cause tire damage. In cold climates, especially during the winter, all pavement breaks should be repaired immediately.
Another hazardous condition often overlooked is accumulated loose material on paved areas and hangar floors. Stones and other foreign materials should also be swept off all the paved areas. In addition, tools, bolts, rivets and other repair materials are sometimes left lying on the aircraft and when the aircraft is moved, these materials drop off. These objects picked up by the tires of another aircraft can cause punctures, cuts, or complete failure of the tire, tube and even the wheel.
With jet aircraft, it is even more important that foreign material be kept off areas used by aircraft.
Hydroplaning This is a condition whereby on wet runways, a wave of water can build up in front of spinning tires and when over-run, tires will no longer make contact with the runway. This results in the complete loss of steering capability and braking action.
Hydroplaning can also be caused by a thin film of 395
water on the runway mixing with the contaminants present. (See figure 9-63.)
Cross cutting of runways has been completed at some of the major airports and reportedly has greatly reduced the danger of hydroplaning. However, the ridges of concrete created by this crosscutting can cause a chevron type of cutting of tread ribs, particularly with the higher pressure tires used on jet aircraft. These cuts are at right angles to the ribs and rarely penetrate to the fabric tread reinforcing strip. Such damage would not be considered cause for remova, unless fabric was exposed due to a piece of tread rib being torn out.
Replacement of this valve can be made by most any gasoline service station or garage, providing they have the proper valve for replacement.
2. Metal valve with rubber base. These are easily recognized since the rubber base is similar to the one used on the all-rubber valve just described. Generally, replacement is made by the same method but it is absolutely necessary that the replacement valve have the same dimensions as the original.
3. Metal valve with a fabric-reinforced rubber base. The base may be cured on top of the tube, or it may be cured into the tube. The metal valve may have to be bent to the proper angle, or angles. Repairing of this type of tube is more difficult because it is necessary to replace the valve pad.
perienced personnel and special equipment are necessary to effect the proper cure of the replacement valve pad to the inner tube.
Repair type valves are also available tor valves mentioned in 2 and 3 above. These are applied by cutting off the original valve and screwing on a replacement repair valve to the spud of the original valve. Follow instructions provided by the manufacturer of these repair type valves.
FiGurE: 9-63. Cross cutting runways reduces danger of hydroplaning.
TUBE REPAIR Most tube repairs are necessary because of valves being broken off or otherwise damaged. However, occasionally, a tube might be cut, punctured, or damaged by the tire tools during mounting or de- Injuries larger than one inch can be repaired by using a reinforcement patch inside the This reinforcement would be the same material that is used for repairing the tube on the outside. An injury smaller than one inch should not need a reinforcement piece.
Chaffing damage caused by the toe of the tire bead, or thinning out of the tube from brake heat should be cause for immediate scrapping of the
SIDEWALL-INFLATED AIRCRAFT TIRES Some tires for small aircraft are manufactured with a valve in the sidewall, thus eliminating the need for machining the wheel to take a conventional valve (see figure 9-04).
There are three general types of valves used in aircraft inner tubes:
1. The rubber valve, which has a rubber stem and a rubber base cured to the outside surface of the inner tube. This valve is similar to those used on inner tubes in passenger car service. FIGURE 9-64. Sidewall-inflated tire.
Inflation as well as checking air pressure, is accomplished by inserting a needle through the rubber sidewall valve, similar to the way footballs and other sporting goods equipment are inhated. Care should be given these needles. If damaged, they may injure the valve, resulting in air loss, particularly when the tire is under load.
Replacing these valves is easy. The only equipment needed is a knife or scissors to cut off the old valve inside the tire, and a piece of string for in- A. Normal B. Wom out serting the replacement valve. It is even possible to replace these valves without completely removing the tire from the wheel.
TIRE INSPECTION SUMMARY Tires in service should be inspected regularly for excessive wear or other conditions which may render the tire unsafe. This will reduce tire costs noticeably and. may prevent a serious accident.
Figure 9-65 shows the most common types of tire wear and damage.
C. Under inflation D. Over inflation A. Open tread splice B. Thrown tread C. Peeled rib D. Tread chunking FIGURE: 9-65. Common types of tire damage: A, Tread wear: B, Tread; C, Sidewall;
D, Carcass; and E, Bead.
B-Cont.
A. Cut B. Blister and tread C. Groove cracking D. Flaking and chipping separation and rib undercutting A. Skid B. Tread rubber reversion C. Chevron cutting D. Fabric fraying A. Circumferential B. Radial cracks C. Weather checking cracks FIGURE 65--COnt.
A. Impact break B. Liner breakdown C. Contamination A. Brake heat damage B. Chaff damage FIGURE 65--Cont.
ANTISKID SYSTEM The purpose of a wheel brake is to bring a rapidly moving aircraft to a stop during ground roll.
It does this by changing the energy of movement into heat energy through the friction developed in the brakes. A feature found in high performance aircraft braking systems is skid control or antiskid protection. This is an important system because if a wheel goes into a skid, its braking value is greatly reduced.
The skid control system performs four functions:
(1) normal skid control, (2) locked wheel skid control, (3) touchdown protection, and (4) failsafe protection. The main components of the system consist of two skid control generators, a skid control box, two skid control valves, a skid control switch, a warning lamp, and an electrical control harness with a connection to the squat switch.
Normal Skid Control Normal skid control comes into play when wheel rotation slows down but has not come to a stop.
When this slowing down happens, the wheel sliding action has just begun but has not yet reached a full scale slide. In this situation the skid control valve removes some of the hydraulic pressure to the wheel. This permits the wheel to rotate a little faster and stop its sliding. The more intense the skid is, the more braking pressure is removed.
The skid detection and control of each wheel is completely independent of the others. The wheel 399
skid intensity is measured by the amount of wheel Skid Control Generator The skid control generator is the unit that measures the wheel rotational speed. It also senses any changes in the speed. It is a small electrical generator, one for each wheel, mounted in the wheel axle. The generator armature is coupled to, and driven by, the main wheel through the drive cap in the wheel. As it rotates, the generator develops a voltage and current signal. The signal strength indicates the wheel rotational speed. This signal is fed to the skid control box through the Skid Control Box The box reads the signal from the generator and senses change in signal strength. It can interpret these as developing skids, locked wheels, brake applications, and brake releases. It analyses all it reads, then sends appropriate signals to solenoids in the skid control valves.
Skid Control Valves The two skid control valves mounted on the brake control valve are solenoid operated. Electric signals from the skid control box actuate the solenoids. If there is no signal (because there is no wheel skidding), the skid control valve will have no effect on brake operation. But, if a skid develops, either slight or serious, a signal is sent to the skid control valve solenoid. This solenoids' action lowers the metered pressure in the line between the metering valve and the brake cylinders.
It does so by dumping fuid into the reservoir return line whenever the solenoid is energized.
Naturally, this immediately relaxes the brake application. The pressure flow into the brake lines from the metering valves continues as long as the pilot depresses the brake pedals. But the flow and pressure is rerouted to the reservoir instead of to the wheel brakes.
The utility system pressure enters the brake control valve where it is metered to the wheel brakes in proportion to the force applied on the pilot's foot pedal. However, before it can go to the brakes, it must pass through a skid control valve.
There, if the solenoid is actuated, a port is opened in the line between the brake control valve and the brake. This port vents the brake application pressure to the utility system return line. This reduces the brake application, and the wheel rotates faster again. The system is designed to apply enough force to operate just below the skid point. This gives the most effective braking.
Pilot Control The pilot can turn off the operation of the antiskid system by a switch in the cockpit. A warning lamp lights when the system is turned off or if there is a system failure.
Locked Wheel Skid Control The locked wheel skid control causes the brake to be fully released when its wheel locks. A locked wheel casily occurs on a patch of ice due to lack of tire friction with the surface. It will occur if the normal skid control does not prevent the wheel from reaching a full skid. To relieve a locked wheel skid, the pressure is bled off longer than in normal skid function. This is to give the wheel time to regain speed. The locked wheel skid control is out of action during aircraft speeds of less than 15-20 mph.
Touchdown Protection The touchdown protection circuit prevents the brakes from being applied during the landing approach even if the brake pedals are depressed.
This prevents the wheels from heing locked when they contact the runway. The wheels have a chance to begin rotating before they carry the full weight of the aircraft. Two conditions must exist before the skid control valves permit brake application. Without them the skid control box will not send the proper signal to the valve solenoids.
The first is that the squat switch must signal that the weight of the aircraft is on the wheels. The second is that the wheel generators sense a wheel speed of over 15-20 mph.
Fail-Safe Protection The fail-safe protection circuit monitors operation of the skid control system. It automatically returns the brake system to full manual in case of system failure. It also turns on a warning light.
LANDING GEAR SYSTEM MAINTENANCE Because of the stresses and pressures acting on the landing gear, inspection, servicing, and other maintenance becomes a continuous process. The most important job in the maintenance of the aircraft landing gear system is thorough, accurate inspections. To properly perform the inspections, all surfaces should be cleaned to ensure that no trouble spots go undetected.
Periodically, it will be necessary to inspect shock struts, shimmy dampers, wheels, wheel bearings, tires, and brakes. During this inspection, check for the presence of installed ground safety locks. Check landing gear position indicators, lights, and warn- 400
ing horns for operation. Check emergency control handles and systems for proper position and condition. Inspect landing gear wheels for cleanliness, corrosion, and cracks. Check wheel tie bolts for looseness. Examine anti-skid wiring for deterioration. Check tires for wear, cuts, deterioration, presence of grease or oil, alignment of slippage marks, and proper inflation. Inspect the landing gear mechanism for condition, operation, and proper adjustment. Lubricate the landing gear, including the nose wheel steering. Check steering system cables for wear, broken strands, alignment, and safetying. Inspect landing gear shock struts for such conditions as cracks, corrosion, breaks, and security. Where applicable, check the brake clearances.
Various types of lubricants are required to lubricate points of friction and wear on the landing gear. These lubricants are applied by hand, an oil can, or a pressure-type grease gun. Before using the pressure-type grease gun, wipe the lubrication fittings clean of old grease and dust accumulations, Up line Down line because dust and sand mixed with a lubricant produce a very destructive abrasive compound. As each fitting is lubricated, the excess lubricant on the fitting and any that is squeezed out of the assembly should be wiped off. Wipe the piston rods of all exposed actuating cylinders; clean them frequently, particularly prior to operation, to prevent damage to seals and polished surfaces.
Periodically, wheel bearings must be removed, cleaned, inspected, and lubricated. When cleaning a wheel bearing, use a suitable cleaning solvent.
(Leaded gasoline should not be used.) Dry the bearing by directing a blast of dry air between the rollers. Do not direct the air so that it will spin the bearing, as it may fly apart and injure nearby persons. When inspecting the bearing, check for defects that would render it unservicable, such as flaked, cracked, or broken bearing surfaces; roughness due to impact pressure or surface wear; corrosion or pitting of the bearing surfaces; discoloration from excessive heat; cracked or broken cages;
Uplock switch Forward latch mechanism Latch cylinder Latch cylinder Emergency release cable Aft latch Sector mechanism
- Sector Latch hook Door - Latch roller FreuRE 9-66. Main gear door latch mechanisms, 401
or scored or loose bearing cups or cones which would affect proper seating on the axle or wheel. If any of these defects exist replace the bearing with a servicable one. To prevent rust or corrosion, lubricate the bearing immediately after cleaning and inspecting it.
To apply lubricant to a tapered roller bearing, place a small amount of the proper lubricant on the palm of the hand. Grasp the cone of the bearing assembly with the thumb and first two fingers of the other hand, keeping the larger diameter of the bearing next to the palm. Move the bearing assembly acroas the hand toward the thumb, forcing the lubricant into the space between the cone and rollers.
Turn the assembly after each stroke until all openings between the rollers are filled with lubricant.
Remove the excess lubricant from the cone and the outside of the cage.
Landing Gear Rigging and Adjustment Occasionally it becomes necessary to adjust the landing gear switches, doors, linkages, latches, and locks to assure proper operation of the landing gears and doors. When landing gear actuating cyl- Latch cylinder inders are replaced and when length adjustments are made, overtravel must be checked. Overtravel is that action of the cylinder piston beyond the move.
ment necessary for landing gear extension and retraction. The additional action operates the landing gear latch mechanism.
Because of the wide variety of aircraft types and designs, procedures for rigging and adjusting landing gear will vary. Uplock and downlock clearances, linkage adjustments, limit switch adjustments, and other landing gear adjustments vary widely with landing gear design. For this reason, always consult the applicable manufacturers maintenance or service manual before performing any phase of landing gear rigging or installation.
Adjusting Landing Gear Latches The adjustment of latches are of prime concern to the airframe mechanic. A latch is used in landing gear systems to hold a unit in a certain position after the unit has traveled through a part of, or all ot, its cycle. For example, on some aircraft, when the landing gear is retracted, each gear is held in the up position by a latch. The same holds true Latch cylinder Latched roller support Latch hook Latch hook (serrated) (latched position) (latched position) Latch roller Latch roller (on door) (on door) •Elongated holes 1/8 ÷ 3/32 inch Plate (serrated) (A) Latch roller clearance (B) Latch roller support adjustment FIGUR: 9.67. Landing gear door latch installations.
when the landing gear is extended. Latches are also used to hold the landing gear doors in the open and closed positions.
There are many variations in latch design. However, all latches are designed to accomplish the same thing. They must operate automatically, at the proper time, and hold the unit in the desired position. A typical landing gear door latch is described in the following paragraphs.
On this particular aircraft, the landing gear door is held closed by two door latches. As shown in figure 9-66, one is installed near the rear of the door. To have the door locked securely, both locks must grip and hold the door tightly against the aircraft structure. The principal components of each latch mechanism shown in figure 9-66 are a hydraulic latch cylinder, a latch hook, a spring loaded crank-and-lever linkage, and a sector. The latch cylinder is hydraulically connected with the landing gear control system and mechanically connected, through linkage, with the latch hook. When hydraulic pressure is applied, the cylinder operates the linkage to engage (or disengage) the hook with (or from) the latch roller on the door. In the gear-down sequence the hook is disengaged by the spring load on the linkage. In the gear-up sequence, spring action is reversed when the closing door is in contact with the latch hook and the cylinder operates the linkage to engage the hook with the latch roller.
Cables on the landing gear emergency extension system are connected to the sector to permit emergency release of the latch rollers. An uplock switch is installed on, and actuated by, each latch to provide a gear-up indication in the cockpit.
With the gear up and the door latched, inspect the latch roller for proper clearance as shown in figure 9-67, view A. On this installation the required clearance is 1/8 +3/32 in. If the roller is not within tolerance it may be adjusted by loosening its mounting bolts and raising or lowering the latch roller support. This may be done due to the elongated holes and serrated locking surfaces of the latch roller support and serrated plate (view B).
Landing Gear Door Clearances Landing gear doors have specific allowable clearances which must be maintained between doors and the aircraft structure or other landing gear doors.
These required clearances can be maintained by adjusting the door hinges and connecting links and trimming excess material from the door if necessary.
On some installations, door hinges are adjusted by placing the serrated hinge and serrated washers in the proper position and torquing the mounting bolts. Figure 9-68 illustrates this type of mounting.
which allows linear adjustments. The amount of linear adjustment is controlled by the length of the elongated bolthole in the door hinge.
Fairing door fitting Hinge support hinge Bushing.
Attach bolt FICURE 9-68. Adjustable door hinge installation.
The distance the landing gear doors open or close depends upon the length of door linkage and the adjustment of the door stops. The manufacturer's maintenance manuals specify the length of door linkages and adjustment of stops or other procedures whereby correct adjustments may be made.
Landing Gear Drag and Side Brace Adjustment The landing gear side brace illustrated in figure 9-69 consists of an upper and lower link, hinged at the center to permit the brace to jackknife during retraction of the landing gear. The upper end pivots on a trunnion attached to the wheel well overhead.
The lower end is connected to the shock strut.
On the side brace illustrated, a locking link is incorporated between the upper end of the shock strut and the lower drag link. Usually in this type installation, the locking mechanism is adjusted so that it is positioned slightly overcenter. This provides positive locking of the side brace and the locking mechanism, and as an added safety feature, prevents inadvertant gear collapse caused by the side brace folding.
To adjust the overcenter position of the side brace locking link illustrated in figure 9-69, place the landing gear in the down position and adjust the lock link end fitting so that the side brace lock link is held firmly overcenter. Manually break the 403
Push-pull Door arm stop Bellcrank U plock tube Door Gear actuator strut B Bellcrank Torque tube Push-pull tube Landing gear Uplock push-pull tube actuator Side link Bellcrank Side brace lock link B
- Spring scale .22 = .03 inches Overcenter Adjustable link FiccR: 9-69. Landing gear schematic showing overcenter adjustments.
lock link and move the landing gear to a position 5 or 6 in. inboard from the down locked position, then release the gear. The landing gear must freefall and lock down when released from this position.
In addition to adjusting overcenter travel, the down lock spring tension must be checked using a spring scale. The tension should be between 40 to 60 Ibs. for the lock link illustrated. The specific tension and procedure for checking will vary on other aircraft.
Landing Gear Retraction Check There are several occasions when a retraction check should be performed, First, a retraction check should be performed during an annual inspection of the landing gear system. Second, when performing maintenance that might affect the landing gear linkage or adjustment, such as changing an actuator, make a retraction check to see whether everything is connected and adjusted properly. Third, it may be necessary to make a retraction check after a hard or overweight landing has been made which may have damaged the landing gear. Closely inspect the gear for obvious damage and then make the retraction check. And finally, one method of locating malfunctions in the. landing gear system is to perform a gear retraction check.
There are a number of specific inspections to perform when making a tetraction check of landing gear. Included are:
(1) Landing gears for proper retraction and extension.
(2) Switches, lights, and warning horn or buzzer for proper operation.