I've seen that airplanes are connected to some wire like in the picture. What is it's name and what is it for?


This is a ground power unit (GPU) which supplies the aircraft with electricity while the generators or the auxiliary power unit (APU) are not running. This is important especially during boarding, when the cabin lighting needs to remain on for passengers to embark or disembark. The GPU is also used to start the APU, which in turn provides electricity to start the engines and the generators.

A ground power unit (GPU) is a vehicle capable of supplying power to aircraft parked on the ground. Ground power units may also be built into the jetway, making it even easier to supply electrical power to aircraft. Many aircraft require 28 V of direct current and 115 V 400 Hz of alternating current. The electric energy is carried from a generator to a connection on the aircraft via 3 phase 4-wire insulated cable capable of handling 261 amps (90 kVA). These connectors are standard for all aircraft, as defined in ISO 6858.
Source: Wikipedia

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  • 5
    $\begingroup$ Nevertheless aircraft often have APU running during boarding, because while GPU provides electricity, it does not provide pressurized air for air-conditioning. $\endgroup$
    – Jan Hudec
    Nov 14 '14 at 12:55
  • 3
    $\begingroup$ @JanHudec - more often than not, the AC is NOT running during boarding, and the airline apologizes that they can't turn it on until the doors are closed. At least that's been my experience in the US. $\endgroup$
    – Floris
    Nov 14 '14 at 16:43
  • 5
    $\begingroup$ @Floris Higher frequency generally means smaller, lighter transformers. $\endgroup$
    – Geobits
    Nov 14 '14 at 16:47
  • 2
    $\begingroup$ @JanHudec It is fairly common to use a source of conditioned air from the ground as well so that the APU isn't running when not necessary. $\endgroup$
    – Lnafziger
    Nov 15 '14 at 16:27
  • 1
    $\begingroup$ @Floris Yes, as I said, it varies from airport to airport. Also, it's possible in some cases that the FAs mean that the aircraft's (significantly more powerful) onboard A/C system can't be started until the door is closed. Especially on particularly hot/sunny days, the external A/C sometimes isn't enough to keep up with the heat, especially with hot air coming in through the open boarding door. $\endgroup$
    – reirab
    Dec 9 '14 at 15:12

It provides power to the plane for when the engines and APU are not running while sitting at the gate to save fuel.

It allows the cabin lights to remain on so the passengers aren't tripping over each other as they board.

The power may also be used to start the APU that will in turn provide the power needed to start the main engines.


There are two kinds of GPUs:

  1. The ones that are fixed and supply power to the aircraft
  2. The ones which are mobile, which are tugged to the stationary aircraft

The cables are connected by groundcrew before the pilot shuts down all engines. It is different from pilot to pilot. The APU remains on while the aircraft is being serviced.

  • $\begingroup$ The APU remains on. Cargo doors are opened . FMC / belt loader start unloading cargo from airplane. The gbu remains on thoughtout unloading and loading of aircraft.In certain cases the gpu might trip for certain unknown reasons $\endgroup$ Jan 27 '15 at 22:05
  • $\begingroup$ GPU is the cable you are talking about in your photo. This is called GPU ground fixed unit at a operating aerodrome. $\endgroup$ Jan 27 '15 at 22:07
  • $\begingroup$ Hello RAYHAN ahmed, welcome to Aviation.SE! To edit your post and add information to it you can use the edit link under your answer. $\endgroup$
    – DeltaLima
    Jan 27 '15 at 22:10
  • $\begingroup$ Gbu means GPU my spelling mistake sorry. $\endgroup$ Jan 27 '15 at 22:10
  • 2
    $\begingroup$ @RAYHANahmed Can you please update About Me section describing what you do. If you just reference about it in an answer, not everyone will understand as they may not know about your other question, where you described it. $\endgroup$
    – Farhan
    Jan 28 '15 at 16:29

It is ground power unit. Due to the technical difficulty on ground to operate APU, which is the source of power for the aircraft. Aircraft engineers connect GPU.

  • $\begingroup$ technical difficulty on ground to operate APU? could you expand on this? $\endgroup$
    – Federico
    Mar 11 '16 at 6:16

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