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
Page 294 AC 43.13-1A 1972 Section 3. JUNCTION BOXES AND TERMINAL STRIPS
783. JUNCTION BOXES. Inspect junction boxes for "oil canning" of the cover and sides, internal shorts due to distortion of the box, internal cleanliness, absence of stray metallic objects, proper grommeting where wires or cables enter the box, and freedom of drain holes from foreign objects or material.
784. INTERNAL ARRANGEMENT. Dlectric cable inside the box should be laced or clamped in such a manner that terminals are not hidden, relay armatures are not fouled, and motion relative to any equipment is prevented. Where marginal clearances are unavoidable, an insulating material should be interposed between currentcarrying parts and any grounded surface.
785. TERMINAL STRIPS. Inspect terminal strips which provide connection of radio and electronic systems to the aircraft electrical system for loose connections, metallic objecta which may have fallen across the terminal strip, dirt and grease accumulation, etc. Such conditions can cause arcing which may result in a fire.
786. PLUGS AND RECEPTACLES. Inspect this type of power connector for loose soldered connections, proper insulation of metallic parts, and fraying of wires in the plug and receptacle inserts.
787.-797. RESERVED.
Par 783 Chap 15
AC 43.13-1A Pago 995 1972 Section 4. POWER SOURCES AND DISTRIBUTION SYSTEMS
798. BATTERY ELECTROLYTE CORROSION. Electrolyte spilled during ground servicing should be neutralized at once with solutions of sodium bicarbonate (for acid electrolyte) or boric acid, vinegar, or a 3 percent solution of acetic acid (for alkaline electrolyte). Residue should be washed off with clean water and the area thoroughly dried.
799. GENERATORS AND ALTERNATORS, Inspect generators and alternators and their associated wiring and distribution systems for wear, damage, general condition, and proper functioning to assure the continued satisfactory operation of the electrical aystem. Frequent visual inspections, operating checks of all electrical circuits and equipment, and replacement or repair when deficiencies are found are effective in minimizing electrical troubles and hazards in aircraft.
short circuit and will generally destroy them instantly.
802. ALTERNATOR/BATTERY CONNECTIONS. Some alternators require that the battery be connected in the circuit initially before it will produce any output.
803, STATIC ELECTRICAL POWER CONVERTERS.
Static power converters employ solid state devices to convert the aircraft primary electrical source voltage to higher values for the operation of radio and electronic equipment. They contain no moving parts and are relatively maintenance free. Various types are available for AC to DC or DC to AC conversion. Exercise care in locating and mounting static converters to insure adequate ventilation for cooling purposes. Heat radiating fins should be kept clean of dirt and other foreign matter which may impair their cooling properties.
800. ALTERNATOR DIODES. Alternators employ diodes for the purpose of converting the alternating current to direct current. These diodes are electronic devices and are particularly susceptible to damage if abused. A diode will allow passage of current in one direction with little resistance, but will allow passage of current in the opposite direction only if the voltage applied exceeds that value for which the device was designed. A voltage surge in the line, if it exceeds the design value, will destroy the diode very quickly.
801. DIODE PROTECTION. The best protection against diode destruction by voltage surges is to make certain that the battery is never disconnected for the aircraft electrical system when the alternator is in operation, The battery acts as a large capacitor and tends to damp out voltage surges. Make certain that the battery is never connected with reversed polarity. This will subject the diodes to a direct
804. CLEANING AND PRESERVATION. Frequent cleaning of electrical and electronic equipment to remove dust, dirt, and grime is recommended. Fine emery cloth may be used to clean terminals and mating surfaces if they appear corroded or dirty. Crocus cloth or very fine sandpaper should be used to polish commutators or slip rings. Use of emery cloth on commutators is not acceptable because metallic particles from the cloth may cause shorting and burning.
805. MISCELLANEOUS CHECK ITEMS. Make frequent checks for miscellaneous irregularities such as loose terminal connections, poorly soldered or loosely swaged terminals, missing safety wire, loose quick-disconnects, broken wire bundle lacing, broken or inadequate wire clamps, and insufficient clearance between exposed current-carrying parts and ground. Replacement or repair should be accomplished as & part of routine maintenance.
Chap 15 Par 798
806. ADJUSTMENT AND REPAIR, Accomplish all adjustment, repair, overhaul, and testing of electrical equipment and systems in accordance with the recommendations and procedures set forth in maintenance instructions or manuals published by the aircraft and equipment manufacturers.
807. ELECTRICAL SWITCH INSPECTION. Special attention should be given to electrical circuit switches, especially the spring-loaded type, during the course of normal airworthiness inspection. An internal failure in this type of switch may allow the switch to remain closed Par 806 AC 43.13-14 1972 even though the toggle or button returns to the "off" position. During inspection, attention should also be given to the possibility that improper switch substitution may have been
808. RADIO EQUIPMENT OPERATION. Determine that the radio and electronic equipment operates satisfactorily throughout the voltage range of the aircraft electrical system under taxi, takeoff, slow cruise, normal cruise, and landing operating conditions.
809.-819. RESERVED.
Chap 15
AC 43.13-1A Page 297 1972 Section 5. NOISE SUPPRESSION
820. GENERAL. Elimination or suppression of sources of radio interference within the aircraft is necessary in order to obtain the optimum performance of airborne radio equipment. This is done by bonding, shielding, and the use of static dischargers.
821. BONDING. Radio equipment should be bonded to the aircraft in order to provide a low impedance ground and to minimize radio interference from static electricity charges. Bonding jumpers should be as short as practicable and be installed in such a manner that the resistance of each connection does not exceed
0.008 ohm. Where a jumper is for radio-noise prevention only and not for current-carrying purposes, a resistance of 0.01 ohm is satisfac-
822. SHIELDING. The most effective method of minimizing engine ignition radio interference is to shield the ignition system. Use a metallic braid covering and special end connectors for ignition wires between the magneto and spark plugs. The primary leads to the magneto and the magneto switch itself should be shielded.
Provide shielded type spark plugs and a shielded metal cover for the magneto if it is not so equipped. All connections in the shielding should be tight metal-to-metal contact.
823, SPARK PLUGS, The engine ignition noise may be suppressed by replacing the spark plugs with resistor spark plugs of a type approved for the engine if it is not feasible to shield the engine ignition system.
824. FILTERS. If an intolerable radio noise level is present despite shielding of the ignition wiring and plugs, it may be necessary to provide a filter between the magneto and magneto switch to reduce the noise. This may consist of a single by-pass capacitor or a combination of capacitors and choke coils. When this is done, the shielding between the filter and magneto switch can usually be eliminated and the special shielded magneto switch need not be used.
Inspect supporting brackets and wiring details for magneto filters for conformance with standard aircraft electrical practice. The reliability of the magneto filter installation should be at least equivalent to that of the remainder of the magneto ground lead installation.
825. PRECIPITATION STATIC, Precipitation static is a general term applied to noise in radio receiving systems caused by precipitation. It is not always caused by true precipitation, such as ice, snow, or rain. Dust, sand, or other airborne particles may cause it. It may be the result of ionization in the exhaust of jet engines.
As a result of precipitation static charging, the electrical potential of the aircraft rises until it reaches the corona threshold. Corona is the discharge of electric current from an object into the surrounding air and occurs as short pulses of current and produces a noise spectrum which contains appreciable energy at radio frequencies. The noise produced is coupled into the aircraft antennas.
826. STATIC DISCHARGERS, Static dischargers are installed on aircrait to bleed off precipitation static before the potential reaches the corona threshold. These dischargers are normally mounted on the control surfaces and other extremities of the aircrait. The three major types in use are: (1) flexible, vinyl-covered, carbon-impregnated braid, (2) semiflexible metallic braid, and (8) null-field.
827, MAINTENANCE OF STATIC DISCHARGERS.
Inspect flexible and semiflexible dischargers for physical security of mounting attachments, wear or abrasion of wicks, missing wicks, etc.
Inspect flexible, vinyl-covered wicks to assure that one inch of the inner braid extends beyond Chap 13 Par 820
Page 298 AC 43.13-1А 1972 the vinyl covering. Null-field discharges are mended tolerances, and inspect for physical epoxy bonded to the aircraft structure. Meas- damage.
ure the resistance of the bond to determine compliance with the manufacturer's recom- 828.-838. RESERVED.
Par 827 Chap 15