Get Chapter 9: Aircraft Electrical System - Faa 2020-2024

An electrical system is an integral and essential component of all but the most simplistic of aircraft designs. The electrical system capacity and complexity varies tremendously between a light, piston-powered, single-engine general aviation aircraft and a modern, multi-engine commercial jet aircraft.

The electrical system is essential to the proper functioning of any modern aircraft and is responsible for running everything from the lights and avionics, to the auxiliary fuel pump and engine starter motor.

An electrical system is an integral and essential component of all but the most simplistic of aircraft designs. The electrical system capacity and complexity varies tremendously between a light, piston-powered, single-engine general aviation aircraft and a modern, multi-engine commercial jet aircraft.

Depending upon the aircraft, generators or alternators are used to produce electricity. These are usually engine driven but may also be powered by an APU, a hydraulic motor or a Ram Air Turbine (RAT). Generator output is normally 115-120V/400HZ AC, 28V DC or 14V DC.

The electrical system is essential to the proper functioning of any modern aircraft and is responsible for running everything from the lights and avionics, to the auxiliary fuel pump and engine starter motor.

Hydraulic pumps are both engine-driven and electrically driven for redundancy. Some airplanes have a ram air turbine that is lowered when electrical power is lost to provide a backup to power a hydraulic pump and limited electrical generator. As for the loss of the engines, all airplanes can glide to a landing.

Depending upon the aircraft, generators or alternators are used to produce electricity. These are usually engine driven but may also be powered by an APU, a hydraulic motor or a Ram Air Turbine (RAT). Generator output is normally 115-120V/400HZ AC, 28V DC or 14V DC.

Running at 115v 400Hz allows the use of smaller transformers. Less energy has to be stored in the transformer core per cycle, so the core can be smaller. A smaller core means a lighter transformer, and reducing weight is a good thing in an aircraft.

Hydraulic pumps are both engine-driven and electrically driven for redundancy. Some airplanes have a ram air turbine that is lowered when electrical power is lost to provide a backup to power a hydraulic pump and limited electrical generator. As for the loss of the engines, all airplanes can glide to a landing.

Most general aviation aircraft operate with either a 12- or 24-volt DC system; 12 volts is more common among aircraft built before the 1980s. The basic components include a storage battery of the proper voltage supplying power for engine starting and emergency power.

Running at 115v 400Hz allows the use of smaller transformers. Less energy has to be stored in the transformer core per cycle, so the core can be smaller. A smaller core means a lighter transformer, and reducing weight is a good thing in an aircraft.

Aircraft software systems. Flight control systems. Landing gear system. Hydraulic system. Electrical system. Engine bleed air system. Avionics. Environmental control system or Cabin control system.

Most general aviation aircraft operate with either a 12- or 24-volt DC system; 12 volts is more common among aircraft built before the 1980s. The basic components include a storage battery of the proper voltage supplying power for engine starting and emergency power.

In an aircraft, the line voltage is about 200 volts, the phase voltage is about 115 volts, and the frequency is 400 Hz. So, an electrical system of an aircraft is said to be a 115V/200V/400Hz/3 Phase system. The 400 Hz is the optimum frequency of the generators used in aircraft.

Aircraft software systems. Flight control systems. Landing gear system. Hydraulic system. Electrical system. Engine bleed air system. Avionics. Environmental control system or Cabin control system.

Cessna-172: 28 Volt DC electrical system. Powered by 60-amp alternator (belt-driven) and a 24-volt battery (left forward side of firewall) Power distribution module (J-box) located on the left forward side of the firewall houses all relays, the alternator control unit, and the external power connector within the module.

In an aircraft, the line voltage is about 200 volts, the phase voltage is about 115 volts, and the frequency is 400 Hz. So, an electrical system of an aircraft is said to be a 115V/200V/400Hz/3 Phase system. The 400 Hz is the optimum frequency of the generators used in aircraft.

Most airplane electrical systems are “single-wire,” meaning that the airframe itself is used as a ground, eliminating the need to run two wires for a positive and ground connection to each electrical component.

Cessna-172: 28 Volt DC electrical system. Powered by 60-amp alternator (belt-driven) and a 24-volt battery (left forward side of firewall) Power distribution module (J-box) located on the left forward side of the firewall houses all relays, the alternator control unit, and the external power connector within the module.

Alternating Current (AC) or Direct Current (DC) In larger aircraft, AC power is used. AC motors have a better power-to-weight ratio and are simpler in design. As bigger aircraft require a lot more electrical power, DC motors and a DC power system become impractical.

Most airplane electrical systems are “single-wire,” meaning that the airframe itself is used as a ground, eliminating the need to run two wires for a positive and ground connection to each electrical component.

Many airplanes in the past were not equipped with an electrical system. They were equipped with a magneto system which supplied electrical energy to the engine ignition system only. Modern airplanes still use an independent magneto system, but in addition are equipped with an electrical system.

Alternating Current (AC) or Direct Current (DC) In larger aircraft, AC power is used. AC motors have a better power-to-weight ratio and are simpler in design. As bigger aircraft require a lot more electrical power, DC motors and a DC power system become impractical.

Many airplanes in the past were not equipped with an electrical system. They were equipped with a magneto system which supplied electrical energy to the engine ignition system only. Modern airplanes still use an independent magneto system, but in addition are equipped with an electrical system.

An electrical system is an integral and essential component of all but the most simplistic of aircraft designs. The electrical system capacity and complexity varies tremendously between a light, piston-powered, single-engine general aviation aircraft and a modern, multi-engine commercial jet aircraft.

The electrical system is essential to the proper functioning of any modern aircraft and is responsible for running everything from the lights and avionics, to the auxiliary fuel pump and engine starter motor.

Depending upon the aircraft, generators or alternators are used to produce electricity. These are usually engine driven but may also be powered by an APU, a hydraulic motor or a Ram Air Turbine (RAT). Generator output is normally 115-120V/400HZ AC, 28V DC or 14V DC.

Hydraulic pumps are both engine-driven and electrically driven for redundancy. Some airplanes have a ram air turbine that is lowered when electrical power is lost to provide a backup to power a hydraulic pump and limited electrical generator. As for the loss of the engines, all airplanes can glide to a landing.

Running at 115v 400Hz allows the use of smaller transformers. Less energy has to be stored in the transformer core per cycle, so the core can be smaller. A smaller core means a lighter transformer, and reducing weight is a good thing in an aircraft.

Most general aviation aircraft operate with either a 12- or 24-volt DC system; 12 volts is more common among aircraft built before the 1980s. The basic components include a storage battery of the proper voltage supplying power for engine starting and emergency power.

Aircraft software systems. Flight control systems. Landing gear system. Hydraulic system. Electrical system. Engine bleed air system. Avionics. Environmental control system or Cabin control system.

In an aircraft, the line voltage is about 200 volts, the phase voltage is about 115 volts, and the frequency is 400 Hz. So, an electrical system of an aircraft is said to be a 115V/200V/400Hz/3 Phase system. The 400 Hz is the optimum frequency of the generators used in aircraft.

Cessna-172: 28 Volt DC electrical system. Powered by 60-amp alternator (belt-driven) and a 24-volt battery (left forward side of firewall) Power distribution module (J-box) located on the left forward side of the firewall houses all relays, the alternator control unit, and the external power connector within the module.

Most airplane electrical systems are “single-wire,” meaning that the airframe itself is used as a ground, eliminating the need to run two wires for a positive and ground connection to each electrical component.

Alternating Current (AC) or Direct Current (DC) In larger aircraft, AC power is used. AC motors have a better power-to-weight ratio and are simpler in design. As bigger aircraft require a lot more electrical power, DC motors and a DC power system become impractical.

Many airplanes in the past were not equipped with an electrical system. They were equipped with a magneto system which supplied electrical energy to the engine ignition system only. Modern airplanes still use an independent magneto system, but in addition are equipped with an electrical system.