K. Aircraft Electrical Systems
On NiCd batteries, what is the minimum cell voltage at the end of the charge cycle? (AM.II.K.K17)
1.55 volts.
What is the frequency of AC voltage used in aircraft? (AM.II.K.K2)
400 Hz.
What is the composition of 60/40 solder? (AM.II.K.K14)
60% tin and 40% lead.
What is meant by a trip-free circuit breaker? (AM.II.K.K5)
A circuit breaker that cannot be closed while a fault exists, regardless of the position of the operating handle.
What two components are normally housed with a vibrator voltage regulator in a single-unit generator control? (AM.II.K.K5)
A current limiter and a reverse-current cutout relay.
What kind of clamp is used to secure a wire bundle to the aircraft structure? (AM.II.K.K13)
A cushioned clamp.
What is meant by a slow-blow fuse? (AM.II.K.K5)
A fuse that will allow more current than its rating to flow for a short period of time, but will open the circuit if more than its rated current continues to flow.
What is an SPDT switch? (AM.II.K.K15)
A single-pole, double-throw switch.
What is a starter-generator? (AM.II.K.K3)
A starter-generator is a generator and a starter combined into a single unit.
What is the advantage of using AC power over DC power? (AM.II.K.K2)
AC voltages can be stepped up to higher voltages, which means that current goes down and smaller wires can be used to save weight. The voltage is stepped back down at the point of use.
What is meant by paralleling the generators in a multi-engine aircraft? (AM.II.K.K1)
Adjusting the voltage regulators so all the generators share the electrical load equally.
What is the main disadvantage of aluminum wire over copper wire for use in an aircraft electrical system? (AM.II.K.K7)
Aluminum wire is more brittle than copper. It is more subject to breakage when it is nicked or when it is subjected to vibration.
What is one of the first things to check if an electrical component does not operate? (AM.II.K.K7)
Always start with simple solutions and move to more complex. Is the component turned on? Is power available? For example, if a light doesn't function is the system turned on, is the aircraft electrical system energized, or is the bulb burnt out?
How does a constant speed drive (CSD) unit maintain a constant output frequency of the AC generator? (AM.II.K.K4)
By maintaining a constant speed of the generator as the engine speed varies.
How does a rotary inverter create AC voltage? (AM.II.K.K6)
By using a DC motor to spin an AC generator.
How are composite aircraft protected from the damage of lightning strikes? (AM.II.K.K10)
By using a conductive copper for aluminum mesh in the outer layers of the composite structure
If no specific instructions are available, which way should the operating handle of an electrical switch move to turn a component on? (AM.II.K.K15)
Forward or upward.
What is the maximum number of wires that should be connected to any single stud in a terminal strip? (AM.II.K.K13)
Four.
Where could you find the part number of a switch in an aircraft electrical system? (AM.II.K.K7)
In the equipment table or bill of materials on the electrical circuit diagram for the aircraft.
What is the function of a fuse or circuit breaker in an aircraft electrical circuit? (AM.II.K.K5)
It protects the wiring from an excess of current. It will open the circuit if enough current flows to heat the wire.
What are the four basic steps of troubleshooting? (AM.II.K.K7)
Know how the system should operate. Observe the way the system is operating. Divide the system into smaller segments to isolate trouble. Look for the obvious problem first.
What are the colors and positions of aircraft position lights? (AM.II.K.K12)
Left side/wing tip—red Right side/wing tip—green Aft—white
What are two principles upon which circuit breakers operate? (AM.II.K.K5)
Magnetic circuit breakers open a circuit when the current creates a strong enough magnetic field. Thermal circuit breakers open a circuit when the current causes enough heat.
What may be provided by the manufacturer to assist in troubleshooting? (AM.II.K.K7)
Manufacturers often provide a troubleshooting logic chart.
Is an automatic-reset circuit breaker approved for aircraft electrical circuits? (AM.II.K.K5)
No, a manual operation is needed to restore service after the circuit breaker has tripped.
How many splices are allowed in a single wire run? (AM.II.K.K15)
One.
What is meant by "flashing" the field of a generator? (AM.II.K.K1)
Restoring the residual magnetism to the frame of the generator. This is done by passing battery current through the field coils in the direction it normally flows when the generator is operating.
What are the two types of inverters found in aircraft? (AM.II.K.K6)
Rotary inverters and static inverters.
What is the smallest size aluminum wire that is approved for use in aircraft electrical systems? (AM.II.K.K7)
Six-gauge.
Why are solderless splices usually better than soldered splices in the wiring of an aircraft electrical system? (AM.II.K.K14)
Soldered joints are usually stiff, and vibration can harden the wire and cause it to break. Solderless splices are designed to keep the joint flexible so vibration cannot cause the wire to break.
What is the difference between soldering and brazing? (AM.II.K.K14)
Soldering is a method of joining metal parts with a molten nonferrous alloy that melts at a temperature below 800°F. Brazing is essentially the same except the brazing alloy melts at a temperature higher than 800°F but lower than the melting temperature of the metal on which it is used.
Why must acid-core solder never be used on electrical wire? (AM.II.K.K14)
The acid causes the wire to corrode.
What does the specific gravity of the electrolyte of a lead-acid aircraft battery indicate? (AM.II.K.K17)
The amount of acid relative to the water in the electrolyte. This is an indication of the state of charge of the battery.
What are the most likely causes of a battery with a distorted or swollen battery case? (AM.II.K.K17)
The battery has been overcharged or over-discharged, causing overheating, or it could be caused by a plugged vent cap.
What two things must you take into consideration when selecting the wire size to use in an aircraft electrical system installation? (AM.II.K.K13)
The current carrying capability of the wire and the voltage drop caused by the current flowing through the wire.
How is a wire bundle protected from chafing where the bundle goes through a hole in a fuselage frame or bulkhead? (AM.II.K.K13)
The edges of the hole are covered with a flexible grommet, and the bundle is secured to the structure with a cushioned clamp.
When routing a fluid line parallel to an electrical wire bundle, which should be on top? (AM.II.K.K7)
The electrical wire bundle should be on top.
Why must a switch be derated if it is used in a circuit that supplies incandescent lamps? (AM.II.K.K8)
The high-inrush current caused by the low resistance of the cold filaments requires that the switches be derated.
What circuit in an aircraft electrical system is not required to have a circuit protective device? (AM.II.K.K5)
The main circuit for starter motors, used during starting only.
What determines the strength of a soldered joint? (AM.II.K.K14)
The mechanical connection of the joint, not the solder.
How is the state of charge determined on a NiCd battery? (AM.II.K.K17)
The only accurate way to determine the state of charge of a NiCd battery is by a measured discharge with a NiCd battery charger and following the manufacturer's instructions.
In aircraft that are of aluminum construction, what is one of the primary design elements for lightning protection? (AM.II.K.K10)
The use of bonding or grounding straps between all major components and flight controls on the airplane.
What are common causes of wire failure in a crimped connector? (AM.II.K.K7)
The wire was not inserted far enough into the connector and/or the connector was excessively crimped.
How many sets of field windings are contained in a starter-generator? (AM.II.K.K3)
There are two sets of field windings. One field is used to start the engine and one is used for the generation of electrical power.
How many electrical phases are in aircraft alternators? (AM.II.K.K2)
Three.
What is the purpose of an inverter? (AM.II.K.K6)
To convert DC electricity to AC electricity.
What is the purpose of aircraft wire shielding? (AM.II.K.K9)
To eliminate electromagnetic interference by applying a metallic covering to the wiring.
What is the purpose of grounding straps on an instrument panel? (AM.II.K.K11)
To ensure electrical continuity from the panel to the airframe for proper system operation and to reduce the potential for EMI.
What is the purpose of wing inspection lights? (AM.II.K.K12)
To permit visual detection of ice formation on wing leading edges while flying at night.
What size aluminum wire would be proper to replace a piece of four-gauge copper wire? (AM.II.K.K7)
Two-gauge. When you substitute aluminum wire for copper wire, use a wire that is two gauge numbers larger.
What are three types of voltage regulators used with aircraft generators? (AM.II.K.K1)
Vibrator-type, carbon-pile type, and solid state-type.
When checking an electrical circuit for proper operation, what are the most efficient measurements (voltage, current, or resistance)? (AM.II.K.K16)
Voltage measurements are usually the quickest way to verify the completeness of the circuit by measuring the voltage at various points through the circuit.
What is an integrated drive generator (IDG)? (AM.II.K.K4)
When a constant speed drive (CSD) is combined within the alternator housing, the assembly is known as an IDG.
What size generator must be used in an aircraft electrical system if the connected electrical load is 30 amps, and there is no way of monitoring the generator output? (AM.II.K.K1)
When monitoring is not practical, the total continuously connected electrical load must be no more than 80% of the rated generator output. This would require a generator with a rating of 37.5 amps. Practically, a 40-amp generator would be installed.
How does a vibrator-type voltage regulator maintain a constant voltage? (AM.II.K.K5)
When the voltage rises above the desired value, an electromagnetic relay opens and inserts a resistor in the generator field circuit, decreasing the field current and lowering the generator output voltage.
Can wire in free air carry the same current as wire in a bundle? (AM.II.K.K7)
Wire in free air may be used to a higher current level than the same size wire in a bundle. Always refer to an electrical wire size selection chart.
What color insulator on a preinsulated solderless connector indicates that the connector is proper for a 10-gauge wire? (AM.II.K.K15)
Yellow.
Can you substitute aluminum wire for copper wire? (AM.II.K.K7)
Yes. However, you must use aluminum wire two wire gauge sizes larger to carry the same current. Aluminum wire should never be used in runs of three feet or less, or in communication and navigation systems.
