CHAPTER 9. AIRCRAFT SYSTEMS AND COMPONENTS

1 9/27/01AC CHG 1 Par 9-1 Page 9-1 CHAPTER 9. AIRCRAFT SYSTEMS AND COMPONENTSSECTION 1. INSPECTION AND MAINTENANCE OF landing GEAR9-1. The landing gear on AIRCRAFT may befixed or retractable. A fixed gear may bewheels, floats, or skis; and for amphibians acombination of floats and Retractable gear on AIRCRAFT is usuallyoperated with hydraulic or electric power, al-though some models of light general aviationaircraft have manual retract SYSTEMS operatedby a lever in the cockpit.(1) In addition to the normal operatingsystem, emergency SYSTEMS are usually pro-vided to ensure that the landing gear can belowered in case of main- system failure.(2) Emergency SYSTEMS consist ofbackup hydraulic SYSTEMS , or stored nitrogengas bottles that can be directed into actuatingcylinders, mechanical SYSTEMS that can be op-erated manually, or free-fall gravity GENERAL INSPECTION.

2 A thor-ough inspection of the landing gear involvesthe entire structure of the gear , including at-tachments, struts, wheels, brakes, actuatingmechanisms for retractable gears, gear hydrau-lic system and valves, gear doors, and all asso-ciated parts. The manufacturer s inspectionprocedures should be followed where CLEANING AND is recommended that only easily removableneutral solutions be used when cleaning land-ing gear COMPONENTS . Any advantage, such asspeed or effectiveness, gained by using clean-ers containing corrosive materials, can bequickly counteracted if these materials becometrapped in close-fitting surfaces and points, such as landing gear up-and-down latches, jack-screws, door hinges, pul-leys, cables, bellcranks, and all pressure-typegrease fittings, should be lubricated after everycleaning prevent possible failure of a component dueto incompatibility or breakdown of the grease,the following should be observed:1.

3 Use only greases approved for use bythe product Never mix different kinds of greasewithout approval from the Follow the manufacturer s instructionsor FAA approved process for cleaning,purging, and lubricating of the obtain proper lubrication of the main sup-port bushings, it may be necessary to jack : Any time the AIRCRAFT is onjacks, check the landing gear mainsupport bushings for wear. Consultthe AIRCRAFT manufacturer s overhaulmanual for specific wear winter operation, excess grease maycongeal and cause increased loads on the gearretraction system , electric motors, and hydrau-lic pumps. This condition can lead to compo-nent malfunctions; therefore, it is recom-mended that cleanliness be stressed during andafter FIXED- gear INSPECTION.

4 Fixedlanding gear should be examined regularly forwear, deterioration, corrosion, alignment, andother factors that may cause failure or unsatis-factory operation. During a 100-hour or an-AC CHG 19/27/01 Page 9-2 Par 9-4nual inspection of the fixed gear , the aircraftshould be jacked up to relieve the aircraftweight. The gear struts and wheels should bechecked for abnormal play and Old AIRCRAFT landing gear that em-ploys a rubber shock (bungee) cord for shockabsorption must be inspected for age, frayingof the braided sheath, narrowing (necking) ofthe cord, and wear at points of contact with thestructure and stretch. If the age of the shockcord is near 5 years or more, it is advisable toreplace it with a new cord. A cord that showsother defects should be replaced, regardless The cord is color-coded to indicatewhen it was manufactured and to determinethe life of the shock cord.

5 According toMIL-C-5651A, the color code for the year ofmanufacture is repeated in cycles of 5 9-1 shows the color of the code threadfor each year and quarter 9-1. Bungee cord color ENDINGWITHCOLORQUARTERCOLOR0 or 5 Black1stRed1 or 6 Green2ndBlue2 or 7 Red3rdGreen3 or 8 Blue4thYellow4 or 9 Yellow1stRedc. The color coding is composed ofthreads interwoven in the cotton sheath thatholds the strands of rubber cord together. Twospiral threads are used for the year coding andone thread is used for the quarter of the yearsheath, yellow and blue would indicatethat the cord was manufactured in 1994 duringApril, May, or Shock struts of the spring-oleo typeshould be examined for leakage, smoothnessof operation, looseness between the movingparts, and play at the attaching points.

6 Theextension of the struts should be checked tomake sure that the springs are not worn or bro-ken. The piston section of the strut should befree of nicks, cuts, and Air-oil struts should undergo an in-spection similar to that recommended forspring-oleo struts. In addition, the extensionof the strut should be checked to see that itconforms to the distance specified by themanufacturer. If an air-oil strut bottoms that is, it is collapsed the gas charge andhydraulic fluid has been lost from the airchamber. This is probably due to a loose ordefective air valve or to defective O-ring : Before an air-oil strut isremoved or disassembled, the airvalve should be opened to make surethat all air pressure is removed. Se-vere injury and/or damage can occuras the result of disassembling a strutwhen even a small amount of air pres-sure is still in the air The method for checking the fluidlevel of an air-oil strut is given in the manu-facturer s maintenance manual.

7 An alternatemeans of servicing an oil strut is to jack up theaircraft, remove the strut s valve cap, releasethe air charge in the strut by depressing thevalve core, remove the strut s valve core, at-tach a clean two-foot rubber or plastic hose tothe threaded portion that houses the valve core,and secure with a hose clamp. Put the otherend of the hose into a clean two quart con-tainer filled with the correct hydraulic fluid forthe strut. Cover the container with a clean ragto prevent spillage. Now, slowly raise thegear/strut assembly either manually or withanother jack under the strut. This will drivethe remaining air out of the strut into the con-tainer of hydraulic fluid. Once the gear is fullyretracted, slowly lower the gear . The hydraulicfluid in the can will be sucked into the this procedure until you cannot hearany more air bubbles in the container when thewheel strut is fully retracted.

8 With the strut9/27/01AC CHG 1 Par 9-4 Page 9-3fully retracted, remove the hose, insert thevalve core, lower the gear , and service the strutwith nitrogen to get the proper strut The entire structure of the landinggear should be closely examined for cracks,nicks, cuts, corrosion damage, or any othercondition that can cause stress concentrationsand eventual failure. The exposed lower endof the air-oleo piston is especially susceptibleto damage and corrosion, which can lead toseal damage, because the strut is compressedand the piston moves past the strut lower seal,causing the seal to leak fluid and air. Smallnicks or cuts can be filed and burnished to asmooth contour, eliminating the point of stressconcentration. If a crack is found in a landing - gear member, the part must be All bolts and fittings should bechecked for security and condition.

9 Bolts inthe torque links and shimmy damper tend towear and become loose due to the operationalloads placed on them. The nose-wheelshimmy damper should be checked for properoperation and any evidence of leaking. All re-quired servicing should be performed in accor-dance with the AIRCRAFT service INSPECTION OF RETRACTABLELANDING gear . Inspection of the retract-able landing gear should include all applicableitems mentioned in the inspection for the fixedgear. In addition, the actuating mechanismsmust be inspected for wear looseness in anyjoint, trunnion, or bearing; leakage of fluidfrom any hydraulic line or unit; and, smooth-ness of operation. The operational check isperformed by jacking the AIRCRAFT according tothe manufacturer s instructions and then oper-ating the gear retracting and extending During the operational test, thesmoothness of operation, effectiveness of up-and-down locks, operation of the warninghorn, operation of indicating SYSTEMS , clear-ance of tires in wheel wells, and operation oflanding- gear doors should be checked.

10 Im-proper adjustment of sequence valves maycause doors to rub against gear structures orwheels. The manufacturer s checklist shouldbe followed to ensure that critical items arechecked. While the AIRCRAFT is still on jacks,the gear can be tested for looseness of mount-ing points, play in torque links, condition ofthe inner strut cylinder, play in wheel bearings,and play in actuating linkages. Emergencyblow down gear bottles should be inspected fordamage and corrosion and weighed to see ifthe bottle is still retaining the Mechanics should be aware that re-tread tires can be dimensionally bigger than a new tire. While this does not pose a prob-lem on fixed landing gear AIRCRAFT , it may pres-ent a serious problem when installed on re-tractable landing gear AIRCRAFT .