710. FUEL TANKS AND CELLS. Welded or riveted fuel tanks that are made of commercially pure aluminum, 3003, 5052, or similar alloys, may be repaired by welding. Tanks made from heat-treatable aluminum alloys are generally assembled by riveting. In case it is necessary to rivet a new piece in a tank, use the same material as used in the tank undergoing repair, and seal the seams with a compound that is insoluble in gasoline. Special sealing compounds are available and should be used in the repair of tanks. Inspect fuel tanks and cells for general condition, security of attachment, and evidence of leakage. Examine fuel tank or cell vent line, fuel line, and sump drain attachment fittings
CAUTION Purge defueled tanks of explosive fuel/air mixtures In accordance with the manufacturers' service instructions. In the absence of such instructions, utilize an inert gas such as CO, as a purgative to assure the total deletion of fuel/air mixtures.
a. Integral Tonks. Examine the interior surfaces and seams for sealant deterioration and corrosion (especially in the sump area). Follow the manufacturer's instructions for repair and cleaning procedures.
b. Internal Metal Tanks. Check the exterior for corrosion and chafing. Dents or other distortion, such as a partially collapsed tank caused by an obstructed fuel tank vent, can adversely affect fuel quantity gauge accuracy and tank capacity. Check the interior surfaces for corrosion. Pay particular attention to the sump area, especially those which are made of cast material. Repairs to the tank may be accomplished in accordance with the practices outlined in Chapter 2 of this handbook.
c. Removal of Flux After Welding. It is especially important, after repair by welding, to completely remove all flux in order to avoid possible corrosion. Promptly upon completion of welding, wash the inaide and outside of the tank with liberal quantities of hot water and then drain. Next, immerse the tank in either a 5 percent nitric or 5 percent sulfuric acid solution. If the tank cannot be immersed, fill the tank with either solution, and wash the outside with the same solution. Permit the acid to re- Par 790 AC 43.13-1A 1972 main in contact with the weld about one hour and then rinse thoroughly with clean water.
Test the efficiency of the cleaning operation by applying some acidified 5 percent silver nitrate solution to a small quantity of the rinse water used last to wash the tank. If a heavy white precipitate is formed, the cleaning is insufficient and the washing should be repeated.
d. Flexible Fuel Cells. Inspect the interior for checking, cracking, porosity, or other signs of deterioration. Make sure the cell retaining fasteners are properly positioned. If repair or further inspection is required, follow the manufacturer's instructions for cell removal, repair, and installation. Do not allow flexible fuel cells to dry out. Preserve them in accordance with the manufacturer's instructions.
711. FUEL TANK CAPS, VENTS, AND OVERFLOW LINES. Inspect the fuel tank caps to determine that they are the correct type and size for the installation.
a. Venfed caps, substituted for unvented caps, may cause loss of fuel or fuel starvation. Similarly, an improperly installed cap that has a special venting arrangement can also cause malfunctions.
b. Unvented caps, substituted for vented caps, will cause fuel starvation and possible collapse of the fuel tank or cell. Malfunctioning of this type occurs when the pressure within the tank decreases as the fuel is withdrawn. Eventually, a point is reached where the fuel will no longer flow, and/or the outside atmospheric pressure collapses the tank. Thus, the effects will occur sooner with a full fuel tank than with one partially filled.
c. Check tank vents and overflow lines thoroughly for condition, obstructions, correct installation, and proper operation of any check valves and ice protection units. Pay particular attention to the location of the tank vents when such information is provided in the manufacturer's service instructions. Inspect for cracked or deteriorated filler opening recess drains, which may allow spilled fuel to accumulate within the wing or fuselage. One method of inspection is to plug the fuel line at the out- Chap 14
AC 43.13-1A 1972 let and observe fuel placed in the filler opening recess. If drainage takes place, investigate condition of the line and purge any excess fuel from the wing.
d. Assure that Aller opening markings are stated according to the applicable airworthinegs requirements and are complete and legible.
712. FUEL CROSSFEED, FIREWALL SHUTOFF, AND TANK SELECTOR VALVES. Inspect these valves for leakage and proper operation as follows:
a. Internal leakage can be checked by placing the appropriate valve in the "off" position, draining the fuel strainer bowl, and observing if fuel continues to flow into it. Check all valves located downstream of boost pumps with the pump(a) operating. Do not operate the pump (8) longer than necessary.
b. External leakage from these units can be a severe fire hazard, especially if the unit is located under the cabin floor or within a similarly confined area. Correct the cause of any fuel stains associated with fuel leakage.
c. Selector Handles. Check the operation of each handle or control to see that it indicates the actual position of the selector valve. Assure that stops and detents have positive action and feel. Worn or missing detents and stops can cause unreliable positioning of the fuel selector
d. Worn Linkage. Inaccurate positioning of fuel selector valves can also be caused by worn mechanical linkage between the selector handle and the valve unit. An improper fuel valve position setting can seriously reduce engine power by restricting the available fuel flow.
Check universal joints, pins, gears, splines, cams, levers, etc., for wear and excessive clearance, which prevent the valve from positioning accurately or from obtaining fully "off" and "on" positions.
e. Assure that required placards are complete and legible. Replace those that are missing or cannot be read easily.
713. FUEL PUMPS. Inspect, repair, and overhaul boost pumps, emergency pumps, auxiliary Chap 14 Pago 283 pumps, and engine-driven pumps in accordance with the appropriate manufacturer's instructions.
714, FUEL FILTERS, STRAINERS, AND DRAINS.
Check each strainer and filter element for contamination. Determine and correct the source of any contaminants found. Heplace throwaway filter elements with the recommended type. Examine fuel strainer bowls to see that they are properly installed according to direction of fuel flow. Check the operation of all drain devices to see that they operate properly and have positive shutoff action.
715. INDICATOR SYSTEMS. Inspect, service, and adjust the fuel indicator systems according to the manufacturer's instructions. Determine that the required placards and instrument markings are complete and legible.
716, TURBINE FUEL SYSTEMS. The use of turbine fuels in aircraft has resulted in two problem areas not normally associated with aviation gasolines: (1) Entrained water (microscopic particles of free water suspended in the fuel) and (2) microbial contaminants.
a. Entrained water will remain suspended in aviation turbine fuels for a considerable length of time. Unless suitable measures are taken, the fine filters used in turbine fuel systems will clog with ice crystals when the temperature of the fuel drops below the freezing temperature of the entrained water. Some fuel systems employ heated fuel filters or fuel heaters to eliminate this problem. Othera rely upon anti-icing fuel additives.
b. Microbial contamination is a relatively recent problem associated with the operation and maintenance of turbine engine fuel systems.
The effecta of these micro-organisms are far reaching. They can cause powerplant failure due to clogging of filters, lines, fuel controls, etc., and the corrosive acids which they produce can lead to structural failure of integra.
tanks. Microbial contamination is generally 88- sociated with fuel containing free water introduced by condensation or other extraneous sources.
Par 911
Page 284 _AC 43.13-7A 1972
c. Maintain turbine engine fuel systems and 717.-727. RESERVED.
use anti-icing and antibacterial additives in accordance with the manufacturer's recommendations.
Par 716 Chap 14
AC 43.13-1A Рабо 385 1972 Section 3. EXHAUST SYSTEMS
728. GENERAL, Any exhaust system failure should be regarded as a severe hazard. Depending upon the location and type of failure, it can result in carbon monoxide (CO) poisoning of crew and passengers, partial or complete engine power loss, or fire. Exhaust system failures generally reach a maximum rate of occurrence at 100 to 200 hours' operating time, and over 50 percent of the failures occur within 400 hours.
729. MUFFLER/HEAT EXCHANGER FAILURES, Approximately one-half of all exhaust system failures are traced to cracks or ruptures in the heat exchanger surfaces used for cabin and carburetor air heat sources. Failures in the heat exchanger's surface (usually the muffler's outer wall) allow exhaust gases to escape directly into the cabin heat system. The failures are, for the most part, attributed to thermal and vibration fatigue cracking in areas of stress concentration; e.g., tailpipe and stack inlet attachment areas (figures 14.14 thru
14.17).
Failures of the spot welds which attach heat transfer pins, as shown in figure 14.15A, can result in exhaust gas leakage. In addition to the carbon monoxide hazard, failure of heat exchanger surfaces can permit exhaust gases to be drawn into the engine induction system and cause engine overheating and power loss.
730. MANIFOLD/STACK FAILURES, Exhaust manifold and stack failures are also usually fatigue-type failures which occur at welded or clamped joints; e.g., stack-to-flange, stack-tomanifold, muffer connections, or crossover pipe connections. Although these failures are primarily a fire hazard, they also present a carbon monoxide problem. Exhaust gases can enter the cabin via defective or inadequate seals at frewall openings, wing strut fittings, doors, and wing root openings. Manifold/stack FIGURE 14.14.-Typical muffler wall fatigue failure at exhaust outlet, (A. Complete mufler assembly with heat shroud removed; B. Detail view of failure.)
failures, which account for approximately 20 percent of all exhaust system failures, reach a maximum rate of occurrence at about 100 hours' operating time. Over 50 percent of the failures occur within 800 hours.
731. INTERNAL MUFFLER FAILURES. Internal failures (baffles, diffusers, etc.) can cause partial or complete engine power loss by restricting Chap 14 Par 728
AC 43.13-1A 1922 FIGURE 14.15.-Typical muffler wall failure. (A. Complete muffler assembly with heat shroud removed; B.
Detall view of failure; C. Cross section of failed muffler.)
FIGURE 14.16 Typical muffler wall fatigue failure. (A.
Complete muffler assembly with heat shroud partially removed; B. Detail view of failure.)
Par 731 Chap 14
AC 43.13-1A Радь 287 1972 FIGURE 14.17.-Typical fatigue failure of muffler end plate at stack inlet.
the flow of the exhaust gases (figures 14.18 thru 14.21). As opposed to other failures, erosion and carbonizing caused by the extreme thermal conditions are the primary causes of internal failures. Engine backfiring and combustion of unburned fuel within the exhaust system are probable contributing factors. In addition, local hot spot areas caused by uneven exhaust gas flow results in burning, bulging, and rupture of the outer muffler wall (figure
14.15). As might be expected, the time required for these failures to develop is longer than that for fatigue failures. Internal muffier failures account for nearly 20 percent of the total number of exhaust system failures. The highest rate of internal failures occur between 500 and 750 hours of operating time. Engine power loss and excessive backpressure caused by exhaust outlet blockage may be averted by the installation of an exhaust outlet guard as shown in figures 14.22a, and 14.22b. The outlet guard may be fabricated from 8/16 stainless steel welding rod. Form the rod into two "U" shaped segments, approximately 3 inches long and weld into the exhaust tail pipe as shown in figure 14.22a so that the guard will extend 2 inches inside the exhaust mufier outlet port.
Installation of an exhaust outlet guard does Chap 14 FIGURE 14.18.-Section of muffler showing typical internal baffle failure.
FIGURE 14.19.-Loose pieces of failed internal baffe.
Par 731
FIGURE 14.20.-Failed internal baffle partially obstructing muffler outlet.
not negate the importance of thorough inspection of the internal parts of the muffler or the necessity of replacing defective mufflers.
732. INSPECTION. Inspect exhaust systems frequently to ascertain complete system integrity.
CAUTION Marking of exhaust system parts-NEVER USE LEAD PENCILS, GREASE PENCILS, ETC., TO MARK EXHAUST SYSTEM PARTS. Carbon deposited by those tools will cause cracka from heat concentration and carbonization of the metal, If you must mark on exhaust system parts, USE CHALK, PRUSSIAN BLUE OR INDIA INK that is carbon free.
o. Prior to any cleaning operation, remove cowling as required to expose the complete exhaust system. Examine cowling and nacelle areas adjacent to exhaust system components for telltale signs of exhaust gas soot indicating possible leakage points. Check to make sure that no portion of the exhaust system is being chafed by cowling, engine control cables, or other components. The exhaust system often operates at red-hot temperatures of 1000 degrees F. or more; therefore, parts such as igni- Par 731 AC 43.15-14 FIGURE 14.21.-Falled internal baffle completely obstructing muffler outlet, FIGURE 14.22a.-Example of exhaust outlet guard.
tion leads, hoses, fuel lines, and flexible air ducts, should be protected from radiation and convection heating by heat shields or adequate clearance.
b. Remove or loosen all exhaust shields, car- Chap 14
AC 43.13-1A 1972 FIGURE 14.22b.-Example of exhaust outlet guard installed.
buretor and cabin heater muffs, shrouds, heat blankets, etc., as required to permit inspection of the complete system.
c. Perform necessary cleaning operations and inspect all external surfaces of the exhaust system for cracke, dents, and missing parts.
Pay particular attention to welds, clamps, supports, and support attachment lugs, bracing, slip joints, stack flanges, gaskets, flexible couplings, etc. (See figures 14.23 and 14.24.) Examine the heel of each bend, areas adjacent to welds, any dented areas, and low spots in the system for thinning and pitting due to internal erosion by combustion products or accumulated moisture. An ice pick or similar pointed instrument is useful in probing suspected areas. Disassemble the system as necessary to inspect internal baffles or diffusers.
d. Should a component be inaccessible for a thorough visual inspection or hidden by nonremovable parts, remove it and check for possible leaks by plugging its openings, applying approximately 2 p.s.i. internal pressure, and submerging it in water. Any leaks will cause bubbles that can be readily detected. Dry thoroughly before reinstallation.
Chap 14 FIGURE 14.28.-Effect of improperly positioned exhaust pipe/mufier clamp,
733. REPAIRS. It is generally recommended that exhaust stacks, mufflers, tailpipes, etc., be replaced with new or reconditioned components rather than repaired. Welded repairs to exhaust systems are complicated by the difficulty of accurately identifying the base metal so that the proper repair materials can be selected.
Changes in composition and grain structure of the original base metal further complicate the repair. However, when welded repairs are necessary, follow the general procedures outlined in paragraph 68 of this handbook. Retain the original contours and make sure that the completed repair has not warped or otherwise affected the alignment of the exhaust system. Repairs or sloppy weld beads which protrude internally are not acceptable since they cause local hot spots and may restrict exhaust gas flow. When repairing or replacing exhaust system components, be sure that the proper hardware and clamps are used. Do not substitute steel or low temperature self-locking nuts for brass or special high temperature locknuts used by the manufacturer. Never reuse old gaskets.
When disassembly is necessary, replace gaskets with new ones of the same type provided by the manufacturer.
Par 731
FIGURE 14.24.-Primary inspection areas (A. Separate system; B. Crossover type system; C. Exhaust/augmentor system.)
AC 43.13-1A 1972
734. TURBOSUPERCHARGER. When a turbosupercharger is included, the exhaust system operates under greatly increased pressure and temperature conditions. Extra precautions should be taken in the exhaust system's care and maintenance. During high altitude operation, the exhaust system pressure is maintained at or near sea level values. Due to the pressure differential, any leaks in the system will allow the exhaust gases to escape with torchlike intensity that can severely damage adjacent structures. A common cause of turbosupercharger malfunction is coke deposits (carbon buildup) in the waste gate unit causing erratic system operation. Excessive deposit buildups may cause the waste gate valve to stick in the closed position, causing an overboost condition.
Coke deposit buildup in the turbosupercharger itself will cause a gradual loss of power in flight and low deck pressure reading prior to takeoff. Experience has shown that periodic decoking, or removal of carbon deposits, is necessary to maintain peak efficiency. Clean, repair, overhaul, and adjust turbosupercharger system components and controls in accordance with the applicable manufacturer's instructions.
735. AUGMENTOR SYSTEMS. Inspect augmentor tubes periodically for proper alignment, security of attachment, and general overall condition. Regardless of whether or not the augmentor tubes contain heat exchanger surfaces, they should be inspected for cracks along with the remainder of the exhaust system. Cracks can present a fire or carbon monoxide hazard by allowing exhaust gases to enter nacelle, wing or cabin areas.
736.-746. RESERVED.
Par 734 Chap 14
AC 43.13-1A Page 291 1972 Chapter 15. RADIO AND ELECTRONIC SYSTEMS Section 1. MAINTENANCE OF RADIO AND ELECTRONIC SYSTEMS
747. GENERAL, The safety of aircraft operated in the National Airspace System is dependent in a large degree upon the satisfactory performance of the airborne radio and electronic systems. Reliability and performance of the system (s) is proportional to the quality of maintenance received and the knowledge of those who perform such maintenance. It is, therefore, important that maintenance be accomplished using the best techniques and practices to assure optimum performance.
The term "system" as used in this chapter means those units of antenna, power source, sensors, receivers, transmitters, and indicators which together perform a function of communications or navigation.
This chapter is not intended to supersede or replace any Federal Aviation Administration regulation or specific manufacturer's instructions pertaining to radio and electronic equipment maintenance. Chapter 11 supplements the information provided in this chapter.
748, MAINTENANCE OF EQUIPMENT. Inspect units or radio/electronic equipment, assemblies, wiring and control systems for damage, general condition, and proper functioning to assure the continuous satisfactory operation of the system. Test, adjust, and repair radio and electronic equipment and systems in accordance with the manufacturer's maintenance instructions, manuals, and applicable Federal Aviation Regulations.
749. REPLACEMENT OF COMPONENTS, Replace damaged or defective components of radio or electronic units with identical items or items equivalent to the original in electrical and mechanical characteristics, operating tolerances, and the ability to function in the physical environmental conditions encountered in the operation of the aircraft.
750. INSPECTION OF INSTALLATIONS, Some items to look for and checks to be made during the inspection are:
o. Damaged or overheated equipment, connections, or wiring.
b. Poor electrical bonding.
c. Improper support of wiring and conduit.
d. Dirty equipment and connections.
e. Loose connections, terminals, plugs, and receptacles.
4. Condition of fuses, circuit breakers, and electric lamps.
g. Insufficient clearance of equipment from mounting rack, insecure or improper mountings.
h. Broken or missing antenna insulators, lead-through insulators, springs, safety wires, etc.
I. Miscellaneous irregularities such as loose quick-disconnects, metal objects in terminal strips or junction boxes, tightness of connections in plugs and receptacles, broken wire bundle lacing, pinched or dented conduit, broken or inadequate cable clamps, etc.
751. CLEANING. Frequent cleaning of radio and electronics equipment is recommended. Dust, dirt, and lint contribute to overheating of equipment, poor ventilation, and malfunctioning. Equipment chassis may be cleaned with a blast of dry air and a small brush. Special attention should be given that ventilation openings in equipment housings are open and free from obstructing lint and dust.
752. CONTACT CLEANERS. When cleaning radio equipment internally, spray cleaners can be used effectively, especially on switching assem- Chap 15 Par 747
blies. There are many contact cleaners on the market which, while they work well on micarta wafer switches, can cause irreparable damage to plastic wafer switches. Do not use contact cleaners on plastic wafer switches unless recommended or known to be harmless to the plastic.
753. OPERATIONAL CHECKS. An operational check is recommended during 100-hour or periodic inspections of radio and electronic sys- Par 752 AC 43.13-1A 1972 tems. Although individual units of equipment may receive bench checks at various times, the proper functioning of a system can best be determined by an operational check in the aircraft. The various units of communications, navigation, weather radar, DME, and tranaponder systems are interdependent upon each other for proper operational performance.
754.-765. RESERVED.
Chap 13
AC 43.13-1A Page 293 1972 Section 2. MAINTENANCE OF WIRING AND CABLES
766. WIRING AND CABLE INTEGRITY. Inspect interconnecting wiring, cables, and conduit betweer various pieces of electronic equipment to determine that they do not rub against the airframe or each other under vibration conditions encountered in flight. Inspect open wiring and cabling for fraying, damage or distortion resulting from heavy objects being placed on it, being stepped on, or being used as hand-
767. PROTECTION FROM FLUIDS. Separate wiring or cables for flammable fluids lines or those which carry fluids which have a deteriorating effect on wire insulation. Wiring or cables should be routed above such lines and securely clamped to the aircraft structure. An arcing fault between an electric cable and a fluid line may puncture the line and result in a fire.
768. WIRE AND CABLE CLAMPS. Inspect wire and cable clamps for proper tightness. Where cables pass through structure or bulkheads, inspect for proper clamping or grommets. Inspect for sufficient slack between the last clamp and the electronic equipment to prevent strain at the cable terminals and minimize adverse effects on shock mounted equipment.
769. CONDUIT, Conduit is manufactured in metallic and nonmetallic materials and in both rigid and flexible forms. Primarily its purpose is for mechanical protection of the cable within. Inspect conduit for proper end fittings, absence of abrasion at the end fittings, and proper clamping. Inspect for distortion, adequate drain points which are free of dirt, grease, or other obstructions, and freedom from abrasion or damage due to moving objects such as aircraft control cables or shifting cargo.
770. PLASTIC WIRE SLEEVING. Inspect plastic wire sleeving for damage due to abrasion, solvents, or hydraulic fluids.
771. ELECTRICAL TAPE. The chemical base of most plastic electrical tape is polyvinylchloride (PVC). This tape is not flame resistant unless it is specially processed to make it so. Some manufacturers are producing flame-resistant PVC tape and have obtained Fire Underwriter's Laboratory (UL) approval which is shown on the wrapping of the container. Unless the tape shows such approval, it should not be used until its flame resistance properties have been determined. A simple test can be made by applying a flame to a sample of unknown tape and comparing its burning qualities to a sample of flame-resistant tape.
Flame resistant or not, PVC will decompose at temperatures above 221° F. (105° C.) with rapid loss of insulating qualities. It is not recommended for use in compartments where temperatures normally approach 221° F. (105° C.)
nor in designated fire zones unless precautions are taken to prevent short circuits to the airframe, shielded wires in bundles, or any other electrical ground, in the event of decomposition.
772,-782. RESERVED.
Chap 15 Рат 766