What Is an Aircraft Ground Power Unit?

An aircraft ground power unit supplies electricity to systems when the pilot turns off the jet engines and parks the plane at the aircraft stand. The aircraft’s electricity requirements and domestic electricity requirements are not the same. Generally, the standard requirement of an aircraft is to have a 110/220 Volt and 50/60 HZ power supply, while a smaller aircraft like a business model will require a 115 Volt and 400 Hz power supply. For private jets, 28 Volts DC supply is the most common.

Why Are Aircraft Ground Power Units Needed?

Jet engines fulfill all the electrical requirements of an aircraft during flight. Jet engines usually create thrust to fly, and they also work as a power plant to supply electricity in all auxiliary systems. The auxiliary system includes control systems, flight instruments, navigational communication systems and devices, electrical motor mechanisms, lighting systems, appliances in the board kitchen, announcement devices, and entertainment systems.

After landing, the pilot generally keeps one jet engine on to provide enough thrust to taxi toward the aircraft stand and to keep all electrical systems charged. If there is a need to fulfill the aircraft’s power requirements, the pilot will switch on the auxiliary power unit. Aircraft do not require thrust at the stand, but electrical power remains on during passenger arrival and aircraft servicing. Aircraft lights need to remain on so the staff can clean the passenger cabin. Furthermore, most electrical systems are kept on to conduct a pilot’s and other technicians’ post-flight inspections. 

The pilot cannot keep the jet engine on while parked as it is dangerous for the ground staff working around an aircraft, and many support activities would not be possible as a result of hazards. Consequently, the pilot has to turn on the auxiliary power unit or utilize the power supply from the aircraft ground power unit.

An aircraft often has an auxiliary power unit installed in the tail that can supply power for all essential electrical and electronic systems. However, auxiliary power units can be quite problematic as they generate a lot of noise that can be inconvenient. They are an engine that produces power by burning fuel which produces carbon dioxide, and they are costly. Therefore, an aircraft ground power unit (AGPU) is encouraged over the auxiliary power unit (APU). 

How Does an Aircraft Ground Power Unit (AGPU) Work?

An aircraft ground power unit is a box with a cable that is installed in the aircraft. The APGU helps in establishing the electricity supply of the aircraft after the pilot turns off the jet engine. The AGPU box is located at the nose of the plane, and the height of the AGPU box is varied based on the model of aircraft. For instance, if we talk about narrow aircraft like the Airbus A320, the height of the AGPU box is around 2.0m. Similarly, for the Boeing 737, it is 1.9m above the ground. The height of the AGPU holder is not reachable for wide-body aircraft like the Boeing 777-300 with a height of 2.8m while the Airbus A350-900 has a 2.58m height above the ground.

The standard set-up of the AGPU box in narrow-body aircraft starts when the mechanic opens the APGU box cover and unlocks the strain strap that works to prevent disconnection of the APGU plug, which can fall on the ground due to its weight. Then, the mechanic will connect the adapter and check that it is connected correctly by checking if the yellow light is on, which means that the aircraft is ready to receive electricity. It is also known as the interlocking LED. When the yellow light blinks, the operator switches on the power button on the adapter. If the LED button turns green, the electrical connection is successfully established.

Since wide-body aircraft need more power, two AGPU holders can plug in two adapters. Two operators are needed for wide-body aircraft, and they also use a three-foot ladder at the aircraft stand to reach the AGPU box and connect the adapter. Apart from this, all steps are the same as discussed in the above paragraph. During departure, the operator reverses the same sequence when the APGU turns off, unhooking the strain strap and removing all AGPU cables to clear the path for aircraft pushback operations.

Types Of Aircraft Ground Power Units Based on Mobility

 The three types of aircraft ground power units based on mobility are as follows:

  • Fixed-to-ground
  • Bridge Mounted
  • Mobile  

Types Of Aircraft Ground Power Units Based on Power Source

The three types of aircraft ground power units based on the source are as follows:

  • Fuel or engine powered AGPU
  • Solid-state AGPU
  • Battery-powered AGPU

Airliners often choose aircraft ground power units due to less noise, less maintenance, and environmental preservation factors. Fuel powers mobile AGPUs as it remains the predominant configuration. On the other hand, battery-powered AGPUs are not very common, and it might take some time to establish them.  


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