(6) Install bonding and grounding connec- (2) Nut plates are used where access to the tions in protected areas whenever possible. nut for repairs is difficult. Nut plates are Bonding jumpers should be kept as short as prac- riveted or welded to a clean area of the ticable. The jumper should not interfere with the structure (figure 11-40).
operation of movable aircraft elements, such as sur- Lockwasher face controls; normal movement of these elements Screw or bolt - Limited to 4 should not result in damage to the bonding jumper. Washer Washer Electrolytic action can rapidly corrode a bonding.
connection if suitable precautions are not observed.
Aluminum alloy jumpers are recommended for most cases; however, copper jumpers can be used to bond together parts made of stainless steel, cadi- Rivet or weld. • Nut-plate mum-plated steel, copper, brass, or bronze. Where FIcURE 11-40. Nut plate bonding or grounding to a contact between dissimilar metals cannot be flat surface.
avoided, the choice of jumper and hardware should be such that corrosion is minimized, and the part most likely to corrode will be the jumper or associated hardware. Figure 11-38 illustrates some proper hardware combinations for making bonding connections. At locations where finishes are removed, a protective finish should be applied to the completed connection to prevent corrosion.
The use of solder to attach bonding jumpers should be avoided. Tubular members should be bonded by means of clamps to which the jumper is attached. The proper choice of clamp material minimizes the probability of corrosion. When bonding jumpers carry a substantial amount of ground return current, the current rating of the jumper should be adequate, and it should be determined that a negligible voltage drop is produced.
Bonding and grounding connections are normally made to flat surfaces by means of through-bolts or screws where there is easy access for installation.
Other general types of bolted connections are as follows:
(1) In making a stud connection (figure 11-39), a bolt or screw is locked securely to the structure, thus becoming a stud.
Grounding or bonding jumpers can be removed or added to the shank of the stud without removing the stud from the struc- Bonding and grounding connections are also made to a tab riveted to a structure. In such cases it is important to clean the bonding or grounding surface and make the connection as through the connection were being made to the structure. If it is necessary to remove the tab for any reason, the rivets should be replaced with rivets one size larger, and the mating surfaces of the structure and the tab should be clean and free of anodic film.
Bonding or grounding connections can be made to aluminum alloy, magnesium, or corrosion-resistant steel tubular structure as shown in figure 11-41, which shows the arrangement of hardware for bonding with an aluminum jumper. Because of the ease with which aluminum is deformed, it is necessary to distribute the screw and nut pressure by means of plain washers.
Hardware used to make bonding or grounding connections should be selected on the basis of mechanical strength, current to be carried, and ease of installation. If connection is made by aluminum or copper jumpers to the structure of a dissimilar material, a washer of suitable material should be installed between the dissimilar metals go that any corrosion will occur on the washer, which is expendable.
ture.
Plate alund Screw is bolt Lockwasher Washer Washer Plain nex Cylindrical surface Cadium-plated Wanker steel Jockmot Cadimum-plated Tenkaal steel lockwasher (timit to 4) netnut FIcURE 11-37. Bonding or grounding connections to a FIcURE 11-39. Stud bonding or grounding to a flat surface. cylindrical surface.
Hardware material and finish should be selected aircraft. Each class of connector has slightly differon the basis of the material of the structure to ent construction characteristics. Classes A, B, C, which attachment is made and on the material of and D are made of aluminum, and class K is made the jumper and terminal specified for the bonding of steel.
or grounding connection. Either a screw or bolt of (I) Class nthe proper size for the specified jumper terminal should be used. When repairing or replacing exist- (2) Class es ing bonding or grounding connections, the same sed type of hardware used in the original connection nt should always be used. be Testing Grounds and Bonds The resistance of all bond and ground connections should be tested after connections are made before re-finishing. The resistance of each connec- - Class tion should normally not exceed 0.003 ohm. Resistance measurements need to be of limited nature only for verification of the existence of a bond, but should not be considered as the sole proof of satisfactory bonding. The length of jumpers, methods, and materials used, and the possibility of loosening the connections in service should also be consid ered. (4) Class st-
CONNECTORS Connectors (plugs and receptacles) facilitate maintenance when frequent disconnection is required. Since the cable is soldered to the connector inserts, the joints should be individually installed and the cable bundle firmly supported to avoid damage by vibration. Connectors have been particularly vulnerable to corrosion in the past, due to condensation within the shell. Special connectors with waterproof features have been developed which may replace non-waterproof plugs in areas where mositure causes a problem. A connector of the same basic type and design should be used when replacing a connector. Connectors susceptible to corrosion difficulties may be treated with a chemically inert waterproof jelly. When replacing connector assemblies, the socket-type insert should be used on the half which is "live" or "hot" after the connector is disconnected, to prevent unintentional grounding.
Types of Connectors Connectors are identified by AN numbers and are divided into classes with the manufacturer's variations in each class. The manufacturer's variations are differences in appearance and in the method of meeting a specification. Some commonly used connectors are shown in figure 11-42. There are five basic classes of AN connectors used in most misture.
(5) Class K-A fireproof connector used in areas where it is vital that the electric current is not interrupted, even though the connector may be exposed to continuous open flame. Wires are crimped to the pin or socket contacts and the shells are made of steel. This class of connector is normally longer than other classes of connectors.
Connector Identification Code letters and numbers are marked on the coupling ring or shell to identify a connector. This code (figure 11-43) provides all the information necessary to obtain the correct replacement for a defective or damaged part.
Many special-purpose connectors have been designed for use in aircraft applications. These include subminiature and rectangular shell connectors, and connectors with short body shells or splitshell construction.
AN3100 AN3102 wall receptacle AN3101 box receptacle cable receptacle AN3106 AN3107 straight plug AN3106 ‚straight plug MCK disconnect plug AN3108 AN3106 angle plug angle plug FIcURE 11-42. AN connectors.
Standard Installation of Connectors Type (straight plug) The following procedures outline one recom- Class mended method of assembling connectors to recept- Size (in 1/16-inch) acles.
Contact arrangement number (1) Locate the proper position of the plug in relation to the receptable by aligning the Contact style (socket) key of one part with the groove or keyway Insert rotation of the other part,
(2) Start the plug into the receptacle with a FICURE 11-43. AN connector marking. light forward pressure and engage the 456
threads of the coupling ring and recepta-
(3) Alternately push in the plug and tighten the coupling ring until the plug is completely seated.
(4) Use connector pliers to tighten coupling rings one sixteenth to one eighth turn beyond fingertight if space around the connector is too small to obtain a good finger grip.
(5) Never use force to mate connectors to receptacles. Do not hammer a plug into ite receptacle; and never use a torque wrench or pliers to lock coupling rings.
A connector is generally disassembled from a receptacle in the following manner:
by hand.
(2) Alternately pull on the plug body and unscrew the coupling ring until the connector is separated.
(3) Protect disconnected plugs and receptacles with caps or plastic bags to keep debris from entering and causing faults.
(4) Do not use excessive force, and do not pull on attached wires.
CONDUIT Conduit is used in aircraft installations for the mechanical protection of wires and cables. It is available in metallic and nonmetallic materials in both rigid and flexible form.
When selecting conduit size for a specific cable bundle application, it is common practice to allow for ease in maintenance and possible future circuit expansion by specifying the conduit inner diameter about 25% larger than the maximum diameter of the conductor bundle. The nominal diameter of a rigid metallic conduit is the outside diameter.
Therefore, to obtain the inside diameter, subtract twice the tube wall thickness.
From the abrasion standpoint, the conductor is vulnerable at the conduit ends. Suitable fittings are affixed to the conduit ends in such a manner that a smooth surface comes in contact with the conductor within the conduit. When fittings are not used, the conduit end should be flared to prevent wire insulation damage. The conduit is supported by clamps along the conduit run.
Many of the common conduit installation problems can be avoided by proper attention to the following details:
(1) Do not locate conduit where it can be used as a handhold or footstep.
(2) Provide drain holes at the lowest point in a conduit run. Drilling burrs should be carefully removed from the drain holes.
(3) Support the conduit to prevent chafing against the structure and to avoid stressing its end fittings.
Damaged conduit sections should be repaired to prevent damage to the wires or wire bundle. The minimum acceptable tube bend radii for rigid conduit as prescribed by the manufacturer's instructions should be followed carefully. Kinked or wrinkled bends in a rigid conduit are normally not Flexible aluminum conduit is widely available in two types: (1) Bare flexible and (2) rubber-cov.
ered conduit. Flexible brass conduit is normally used instead of flexible aluminum conduit, where necessary to minimize radio interference. Flexible conduit may be used where it is impractical to use rigid conduit, such as areas that have motion between conduit ends or where complex bends are necessary. Transparent adhesive tape is recommended when cutting flexible tubing with a hacksaw to minimize fraying of the braid.
ELECTRICAL EQUIPMENT INSTALLATION This section provides general procedures and safety precautions for installation of commonly used aircraft electrical equipment and components. Electrical load limits, acceptable means of controlling or monitoring electrical loads, and circuit protection devices are subjects with which mechanics must be familiar to properly install and maintain aircraft electrical systems.
Electrical Load Limits When installing additional electrical equipment that consumes electrical power in an aircraft, the total electrical load must be safely controlled or managed within the rated limits of the affected components of the aircraft's power-supply system.
Before any aircraft electrical load is increased, the associated wires, cables, and circuit protection devices (fuses or circuit breakers) should be checked to determine that the new electrical load (previous maximum load plus added load) does not exceed the rated limits of the existing wires, cables, or protection devices.
The generator or alternator output ratings prescribed by the manufacturer should be compared 457
with the electrical loads which can be imposed on the affected generator or alternator by installed equipment. When the comparison shows that the probable total connected electrical load can exceed cal hoe the output load limits of the generator (s) or alternator (s), the load should be reduced so that an overload cannot occur. When a storage battery is part of the electrical power system, ensure that the battery is continuously charged in fight, except when short, intermittent loads are connected such as a radio transmitter, a landing-gear motor, or other similar devices which may place short-time demand loads on the battery.
Controlling or Monitoring the Electrical Load Placards are recommended to inform crewmembers of an aircraft about the combination of electrical loads that can safely be connected to the power source.
In installations where the ammeter is in the battery lead, and the regulator system limits the maximum current that the generator or alternator can deliver, a voltmeter can be installed on the system bus. As long as the ammeter does not read idis.
charge" (except for short, intermittent loads such as operating the gear and flaps) and the voltmeter remains at "system voltage," the generator or alternator will not be overloaded.
In installations where the ammeter is in the generator or alternator lead, and the regulator system does not limit the maximum current that the generator or alternator can deliver, the ammeter can be redlined at 100% of the generator or alternator rating. If the ammeter reading is never allowed to exceed the red line, except for short, inermittent loads, the generator or alternator will not be overloaded.
Where the use of placards or monitoring devices is not practicable or desired, and where assurance is needed that the battery in a typical small aircraft generator/battery power source will be charged in flight, the total continuous connected electrical load may be held to approximately 80% of the total rated generator output capacity. (When more than one generator is used in parallel, the total rated output is the combined output of the installed generators.)
When two or more generators are operated in parallel and the total connected system load can exceed the rated output of one generator, means must be provided for quickly coping with the sudden overloads which can be caused by generator or engine failure. A quick load reduction system, or a specified procedure whereby the total load can be reduced to a quantity which is within the rated capacity of the remaining operable generator (s), can be employed.
Electrical loads should be connected to inverters, alternators, or similar aircraft electrical power sources in such a manner that the rated limits of the power source are not exceeded, unless some type of effective monitoring means is provided to keep the load within prescribed limits.
Circuit Protection Devices Conductors should be protected with circuit breakers or fuses located as close as possible to the electrical power source bus. Normally, the manufacturer of the electrical equipment specifies the fuse or circuit breaker to be used when installing equipment.
The circuit breaker or fuse should open the circuit before the conductor emits smoke. To accomplish this, the time current characteristic of the protection device must fall below that of the associated conductor. Circuit protector characteristics should be matched to obtain the maximum utilization of the connected equipment.
Figure 11-11 shows an example of the chart used in selecting the circuit breaker and fuse protection for copper conductors. This limited chart is applicable to a specific set of ambient temperatures and wire bundle sizes, and is presented as a typical example only. It is important to consult such guides before selecting a conductor for a specific purpose.
For example, a wire run individually in the open air may be protected by the circuit breaker of the next higher rating to that shown on the chart.
Wire AN Circuit Fuse amp.
gage copper breaker amperage 22 20 7.5 18 10 16 15 14 20 12 30 10 40 8 50 80 4 100 2 125 150 FIcURE 11-44. Wire and circuit protector chart.
All re-settable circuit breakers should open the Nominal system Type of load Derating circuit in which they are installed regardless of the voltage factor position of the operating control when an overload 24 v. d.c. Lamp 8 or circuit fault exists. Such circuit breakers are 24 v. d.c. Inductive referred to as "trip-free." Automatic re-set circuit (Relay-Solenoid) 4 breakers automatically re-set themselves. They 24 v. d.c. Resistive (Heater) 2 should not be used as circuit protection devices in 24 v. d.c. Motor 3 12 v. d.c. Lamp 5 12 v. d.c. Inductive (Relay-Solenoid) 2 A specifically designed switch should be used in 12 v. d.c. Resistive (Heater) 1 all circuits where a switch malfunction would be 12 v. d.c. Motor 2 hazardous. Such switches are of rugged construction and have sufficient contact capacity to break, FIGURE 11-45. Switch derating factors.
make, and carry continuously the connected load current. Snap-action design is generally preferred to obtain rapid opening and closing of contacts regardless of the speed of the operating toggle or plunger, thereby minimizing contact arcing.
The nominal current rating of the conventional aircraft switch is usually stamped on the switch housing. This rating represents the continuous current rating with the contacts closed. Switches should be derated from their nominal current rating for the following types of circuits:
(1) High rush-in circuits- Circuits containing incandescent lamps can draw an initial current which is 15 times greater than the continuous current. Contact burning or welding may occur when the switch is stored in solenoid coils or relays is re- circuits-Magnetic hen tho energy leased and appears as an arc when the
(3) Motors-Direct-current motors will draw several times their rated current during starting, and magnetic energy stored in their armature and field coils is released when the control switch is opened.
The chart in figure 11-45 is typical of those available for selecting the proper nominal switch rating when the continuous load current is known.
This selection is essentially a derating to obtain reasonable switch efficiency and service life.
Hazardous errors in switch operation can be avoided by logical and consistent installation. Twoposition "on-off" switches should be mounted so that the "on" position is reached by an upward or forward movement of the toggle. When the switch controls movable aircraft elements, such as landing gear or flaps, the toggle should move in the same direction as the desired motion. Inadvertent operation of a switch can be prevented by mounting a suitable guard over the switch.
Relays Relays are used as switching devices where a weight reduction can be achieved or electrical controls can be simplified. A relay is an electrically operated switch and is therefore subject to dropout under low system voltage conditions. The foregoing discussion of switch ratings is generally applicable to relay contact ratings.
AIRCRAFT LIGHTING SYSTEMS Aircraft lighting systems provide illumination for both exterior and interior use. Lights on the exterior provide illumination for such operations as landing at night, inspection of icing conditions, and safety from midair collision. Interior lighting provides illumination for instruments, cockpits, cabins, and other sections occupied by crewmembers and passengers. Certain special ights, such as indicator and warning lights, indicate the operational status of equipment.
Exterior Lights Position, anti-collision, landing, and taxi lights are common examples of aircraft exterior lights.
Some lights, such as position lights and anti-collision lights, are required for night operations. Other types of exterior lights, such as wing inspection lights, are of great benefit for specialized flying operations.
Position Lights Aircraft operating at night must be equipped with position lights that meet the minimum requirements specified by the Federal Aviation Regulations. A set of position lights consist of one red, one 459
A. Tail position light unit.
B. Wingtip position light unit.
FIGURE 11-46. Position lights.
green, and one white light. Position lights are sometimes referred to as "navigation" lights. On many aircraft each light unit contains a single lamp mounted on the surface of the aircraft (A of figure 11-16). Other types of position light units contain two lamps (B of figure 11-46), and are often streamlined into the surface of the aircraft structure The green light unit is always mounted at the extreme tip of the right wing The red unit is mounted in a similar position on the left wing The white unit is usually located on the vertical stabilizer in a position where it is clearly visible through a wide angle from the rear of the aircraft The wingtip lamps and the tail lamps are controlled by a double-pole, single-throw switch in the pilot's compartment. On "dim", the switch connects a resistor in series with the lamps Since the resistor decreases current flow, the light intensity is reduced. On "bright", the resistor is shorted out of the circuit, and the lamps glow at full brilliance On some types of installations a switch in the pilot's compartment provides for steady or flashing operation of the position lights. For flashing operation, a flasher mechanism is usually installed in the position light circuit. It consists essentially of a motor-driven camshaft on which two cams are mounted and a switching mechanism made up of two breaker arms and two contact screws. One breaker arm supplies d.c. current to the wingtip light circuit through one contact screw, and the other breaker arm supplies the tail light circuit through the other contact screw. When the motor rotates, it turns the camshaft through a set of reduction gears and causes the cams to operate the Right wing tip Н В light, green Dim. (sw. open) Clear Flasher mech 10 ^ Bright (sw. closed) tail light
• Кк
• Flash light, red
• Steady FIGURE 11-47. Position light circuitry.
28 v.d.c. main bus 10A Left wing tip light _B Navigation lights Tail light Right wing tip light B FIGURE 11-48. Single-circuit position light circuitry without flasher.
breaker which opens and closes the wing and tail light circuits alternately. Figure 11-47 is a simplified schematic diagram of a navigation light circuit which illustrates one type of position light circuitry.
The schematic diagram of another type of position light circuitry is shown in figure 11-48. Control of the position lights by a single on-off toggle switch provides only a steady illumination. There is no flasher and no dimming rheostat.
There are, of course, many variations in the position light circuits used on different aircraft. All circuits are protected by fuses or circuit breakers, and many circuits include flashing and dimming equipment. Still others are wired to energize a spesuch a location that the light will not affect the vision of the crewmember or detract from the conspicuousness of the position lights. In some cases one of the lights is mounted on the underside of the fuselage.
The simplest means of installing an anti-collision light is to secure it to a reinforced fuselage skin panel, as shown in figure 11-49.
Anti-collision light Fuselage skin cial warning light dimming relay, which causes all the cockpit warning lights to dim perceptibly when ~ Existing stringer the position lights are illuminated. Small aircraft are usually equipped with a simpli- Existing stringer fied control switch and circuitry. In some cases, one Approximately Reinforcing doubler control knob or switch is used to turn on several one inch spacing sets of lights; for example, one type utilizes a con- of %" min, dia. rivet trol knob, the first movement of which turns on the position lights and the instrument panel lights. Further rotation of the control knob increases the intensity of only the panel lights. A flasher unit is seldom included in the position light circuitry of very light aircraft, but is used in small twin-engine aircraft.
Anti-collision Lights An anti-collision light system may consist of one or more lights. They are rotating beam lights which FIcURE 11-49. Typical anti-collision light installation in are usually installed on top of the fuselage or tail in an unpressurized skin panel.
Anti-collision lights Oscillating mirrors
- Vertical stabilizer FIGURE: 11-51. Anti-collision light.
Light mounting fairing Mounting ring Vertical stabilizer FIcURE 11-50. Typical anti-collision light installation in a vertical stabilizer, An anti-collision light is often installed on top of the vertical stabilizer if the cross section of the stabilizer is large enough to accommodate the installation, and if aircraft flutter and vibration characteristics are not adversely affected. Such installations should be located near a spar, and formers should be added as required to stiffen the structure near the light. Figure 11-50 shows a typical anticollision light installation in a vertical stabilizer.
An anti-collision light unit usually consists of one or two rotating lights operated by an electric motor.
The light may be fixed, but mounted under rotating mirrors inside a protruding red glass housing. The mirrors rotate in an arc, and the resulting flash rate is between 40 and 100 cycles per minute. (See figure 11-51.) The anti-collision light is a safety light to warn other aircraft, especially in congested areas.
lined into the aircraft surface. Each light may be controlled by a relay, or it may be connected directly into the electric circuit.
Since icing of the lamp lenses reduces the illumination quality of a lamp, some installations use retractable landing lamps (figure 11-52). When the lamps are not in use, a motor retracts them into receptacles in the wing where the lenses are not exposed to the weather.
As shown in figure 11-53, one type of retractable landing light motor has a split-field winding. Two of the field winding terminals connect to the two outer terminals of the motor control switch through the points of contacts C and D, while the center terminal connects to one of two motor brushes. The brushes connect the motor and magnetic brake sole- Landing Lights Landing lights are installed in aircraft to illuminate runways during night landings. These lights are very powerful and are directed by a parabolic reflector at an angle providing a maximum range of illumination. Landing lights are usually located midway in the leading edge of each wing or stream- FICURE: 11-52. Retractable landing light.
noid into the electric circuit. The points of contact C are held open by the geared quadrant of the landing lamp mechanism. The points of contact D are held closed by the tension of the spring to the right of the contacts. This is a typical arrangement of a landing lamp circuit when the landing lamp is retracted and the control switch is in the "off" position. No current flows in the circuit, and neither the motor nor the lamp can be energized.
When the control switch is placed in the upper, or "extend," position (figure 11-53), current from the battery flows through the closed contacts of the switch, the closed contacts of contact D, the center terminal of the field winding, and the motor itself.
Current through the motor circuit energizes the brake solenoid, which withdraws the brake shoe from against the motor shaft, allowing the motor to turn and lower the lamp mechanism. After the lamp mechanism moves about 10°, contact A touches and rides along the copper bar B. In the meantime, relay F is energized, and its contacts close. This permits current to flow through the copper bar B, contact A, and the lamp. When the lamp mechanism F relay Extend Retrac Field coil B Magnetic brake Brake solenoid Mechanical linkage Brake spring is completely lowered, the projection at the top of the gear quadrant pushes the D contacts apart, opens the circuit to the motor, and causes the de-energized brake solenoid to release the brake. The brake is pushed against the motor shaft by the spring, stopping the motor and completing the lowering operation.
To retract the landing lamp, the control switch is placed in the "retract" position (figure 11-53). The motor and brake circuits are completed through the points of contact C, since these contacts are closed when the gear quadrant is lowered. This action completes the circuit, the brake releases, the motor turns (this time in the opposite direction) and the landing light mechanism is retracted. Since switching to "retract" breaks the circuit to relay F, the relay contacts open, disconnecting the copper bar and causing the landing lamp to go out. When the mechanism is completely retracted, contact points C open, and the circuit to the motor is again broken, the brake applied, and the motor stopped.
Retractable landing lights that can be extended to any position of their extension are employed on some aircraft. Landing lights used on high-speed aircraft are usually equipped with an airspeed pressure switch which prevents extension of landing lights at excessive airspeeds. Such switches also cause retraction of landing lights if the aircraft exceeds a predetermined speed.
Many large aircraft are equipped with four landing lights, two of which are fixed and two retractable. Fixed lights are usually located in either the wing root areas or just outboard of the fuselage in the leading edge of each wing. The two retractable lights are usually located in the lower outboard surface of each wing, and are normally controlled by separate switches. On some aircraft, the fixed Taxi light Inboard landing light FIcURE 11-53. Landing light mechanism and circuit. FIGURE 11-54. Fixed landing light and taxi light.
landing light is mounted in an area with a taxi light, as shown in figure 11-54.
Taxi Lights Taxi lights are designed to provide illumination on the ground while taxiing or towing the aircraft to or from a runway, taxi strip, or in the hangar area.
Taxi lights are not designed to provide the degree of illumination necessary for landing lights;
150. to 250-watt taxi lights are typical on many medium and heavy aircraft.
On aircraft with tricycle landing gear, either single or dual taxi lights are often mounted on the non-steerable part of the nose landing gear. As illustrated in figure 11-55, they are positioned at an oblique angle to the center line of the aircraft to provide illumination directly in front of the aircraft and also some illumination to the right and left of the aircraft's path. On some aircraft the dual taxi lights are supplemented by wingtip clearance lights controlled by the same circuitry.
Taxi lights are also mounted in the recessed areas of the wing leading edge, often in the same area with a fixed landing light.
Many small aircraft are not equipped with any type of taxi light, but rely on the intermittent use of a landing light to illuminate taxiing operations. Still other aircraft utilize a dimming resistor in the landing light circuit to provide reduced illumination for taxing. A typical circuit for dual taxi lights is shown in figure 11-56.
Some large aircraft are equipped with alternate taxi lights located on the lower surface of the aircraft, aft of the nose radome. These lights, operated by a separate switch from the main taxi lights, illuminate the area immediately in front of and below the aircraft nose.
Wing Inspection Lights Some aircraft are equipped with wing inspection lights to illuminate the leading edge of the wings to permit observation of icing and general condition of these areas in flight. On some aircraft, the wing inspection light system (also called wing ice lights) consists of a 100-watt light mounted flush on the outboard side of each nacelle forward of the wing.
These lights permit visual detection of ice formation on wing leading edges while flying at night. They are also often used as floodlights during ground servicing. They are usually controlled through a relay by an "on-off" toggle switch in the cockpit.
Some wing inspection light systems may include or be supplemented by additional lights, sometimes called nacelle lights, that illuminate adjacent areas such as cowl flaps or the landing gear. These are normally the same type of lights and can be controlled by the same circuits.
MAINTENANCE AND INSPECTION OF LIGHTING
SYSTEMS Inspection of an aircraft's lighting systems normally includes checking the condition and security of all visible wiring, connections, terminals, fuses, and switches. A continuity light or meter can be used in making these checks, since the cause of many troubles can often be located by systematically testing each circuit for continuity.
Switch D.C. bus FIGURE 11-55. Taxi lights mounted on non-steerable portion of nose landing gear. FIcURE 11-56. Typical taxi light circuit.
Indicator Indicator Indicat or Dry cells! lamp Dry cells lamp lamp Out Alligator Alligator Alligator clips alips clips Insulated wire disconnected Open Short Ground from terminals A. B. C. D.
FIcURE 11-57. Continuity testing with a continuity tester.
All light covers and reflectors should be kept clean and polished. Cloudy reflectors are often caused by an air leak around the lens.
The condition of the sealing compound around position light frames should be inspected regularly.
Leaks or cracks should be filled with an approved sealing compound.
Care should be exercised in installing a new bulb in a light assembly, since many bulbs fit into a socket in only one position and excessive force can cause an incomplete or open circuit in the socket area.
Circuit testing, commonly known as troubleshooting is a means of systematically locating faults in an electrical system. These faults are usually of three kinds:
(1) Open circuits in which leads or wires are broken.
(2) Shorted circuits in which grounded leads cause current to be returned by shortcuts to the source of power.
(3) Low power in circuits causing lights to burn dimly and relays to chatter. Electrical troubles may develop in the unit or in the wiring. If troubles such as these are carefully analyzed and systematic steps are taken to locate them, much time and energy not only can be saved, but damage to expensive testing equipent often can be avoided. (For a more extensive treatment of circuit testing than the summary provided here, refer to Chapter 8, Airframe and Powerplant Mechanics General Handbook, AC 05-9A.)
The equipment generally used in testing lighting circuits in an aircraft consists of a voltmeter, test light, continuity meter, and ohmmeter.
Although any standard d.c. voltmeter with flexible leads and test prods is satisfactory for testing circuits, portable voltmeters especially designed for test purposes are usually used.
The test lamp consists of a low wattage aircraft light. Two leads are used with this light.
Continuity testers vary somewhat. One type consists of a small lamp connected in series with two small batteries (flashlight batteries are very suitable) and two leads. (See A of figure 11-57.) Another type of continuity tester contains two batteries connected in series with a d.c. voltmeter and two test leads. A completed circuit will be registered by the voltmeter.
Whenever generator or battery voltage is available, the voltmeter and the test light can be used in circuit testing, since these sources of power will activate the test light and the voltmeter.
If no electrical power is available (the circuit is dead), then the continuity tester is used. The selfcontained batteries of the continuity tester force current through the circuit, causing the continuity meter to indicate when the circuit being tested is completed. When using the continuity meter, the circuit being tested should always be isolated from all other circuits by removing the fuse, by opening the switch, or by disconnecting the wires.
Figure 11-57 illustrates techniques which may be 465