What is an aircraft GPU, and how is it used?

In aviation, GPU stands for ground power unit: an external source that supplies an aircraft with electrical power while it is parked. It runs cockpit, cabin and service systems without using the engines or auxiliary power unit (APU), and can support some engine starts when the aircraft has a compatible electric starting system.

Here in our Aviation & Real-World Flying section, GPU means ground equipment, not the graphics processing unit in a simulator PC or console. Airport staff may call it a ground-power cart even when it is a fixed supply at the stand.

What is the full form of GPU in aviation?

The full form of GPU in aviation is ground power unit, specifically an approved external electrical source for an aircraft on the ground. Its cable connects to the aircraft’s external-power receptacle; the aircraft then checks and accepts the supply through its electrical control and contactor system.

Once accepted, ground power can energise selected buses much like an onboard generator. It is used during boarding, cleaning, catering, maintenance and longer ground stops, reducing aircraft fuel use and APU running time.

What types of airport GPU are used?

An airport GPU may be fixed at the parking stand or mobile enough to tow or drive between aircraft. Common arrangements include:

• Fixed electrical ground power supplied from airport infrastructure, often through a cable mounted near the stand or passenger bridge.
• Engine-driven mobile GPUs that generate aircraft-compatible electricity independently.
• Battery-powered carts, which avoid local exhaust and are usually quieter than engine-driven equipment.
• Mains-powered mobile converters that convert an available electrical supply to the voltage and frequency required by the aircraft.

These units are not automatically interchangeable. Output standard, connector, continuous capacity and short-duration starting capacity must all suit the aircraft.

What does an aircraft GPU power?

An aircraft GPU powers approved electrical buses and equipment while the aeroplane is parked. Depending on the aircraft configuration and available capacity, that may include:

• Cockpit displays, radios, navigation equipment and flight-management computers.
• Cabin, cockpit, exterior and maintenance lighting.
• Fuel pumps, electrically driven hydraulic pumps and other service equipment.
• Ventilation fans, galleys, entertainment systems and passenger-service loads.
• Battery charging through the aircraft’s own charging and protection system.
• Engine controls, ignition circuits and electrically powered starters.

Connecting a GPU does not guarantee that every bus or high-demand load will be available. The aircraft may shed non-essential equipment, and crews may leave galleys, pumps or electrically driven air conditioning off if the source cannot support the total load.

Cabin cooling causes particular confusion. A GPU can run fans or electrically powered cooling equipment, but it does not normally provide pneumatic air. Aircraft using bleed-air air-conditioning packs may need the APU or a separate pre-conditioned-air unit.

What voltage and frequency does an aircraft GPU provide?

A GPU must provide the voltage, frequency, phase, polarity and capacity specified for that aircraft. Common arrangements include:

These are common examples rather than universal standards. An apparently compatible plug does not prove that the source is suitable. Aircraft protection may reject power for incorrect voltage, frequency or phase sequence, while an undersized unit may work for light cockpit loads but trip when pumps, galleys or a starter are switched on.

How is ground power connected to a plane?

Ground power is physically connected by trained ground personnel and then accepted or selected from the cockpit. Exact procedures vary by aircraft and operator, but the normal logic is:

1. Secure the aircraft. Apply the required parking-brake and chock precautions, establish a safe area around the receptacle and follow the operator’s engine and anti-collision-light rules.
2. Confirm compatibility. Check the required AC or DC standard, power rating and connector against the aircraft placard and approved documentation.
3. Inspect the equipment. Look for damaged pins, contamination, moisture, overheated contacts, cable defects or an insecure receptacle.
4. Connect the cable. Put the GPU in the connection-safe state specified by its instructions, fully seat the keyed plug and route the cable where vehicles and personnel cannot pull or crush it.
5. Make power available. Start or enable the GPU as required and allow its output to stabilise. A cockpit indication such as AVAIL, where fitted, means acceptable power has reached the aircraft; it does not necessarily mean the buses are powered.
6. Accept the supply. Select EXT PWR or the aircraft’s equivalent control, then check voltage, frequency, contactor, generator and bus indications before adding major loads.
7. Transfer before disconnecting. Bring an APU or engine generator online, confirm that it has taken the load, deselect or remove external power, and only then disconnect and stow the cable.

Removing a connector while it is carrying load can cause arcing, burned pins and an immediate loss of aircraft power. Some aircraft transfer sources automatically and others require crew action, so an indication that the APU or engine is running is not by itself proof that its generator is powering the buses.

What is the difference between a GPU and an APU?

A GPU is external ground equipment, while an APU is installed in the aircraft and travels with it.

Crews generally choose a GPU when suitable ground electricity is available and pneumatic air is not needed. The APU provides independence from airport equipment and may supply services that an electrical GPU cannot; our deeper explanation of onboard APU operation covers those functions and limitations.

A GPU should also not be confused with a pre-conditioned-air unit, which supplies heated or cooled air, or an air-start unit, which delivers compressed air. A combined ground-service machine may contain more than one function, but its electrical output is still distinct from pneumatic air.

Can a GPU start an aircraft engine?

A GPU can start or support the start of some aircraft engines, but only when the starting system and ground unit are designed for it. The decisive issue is whether the starter needs electricity or compressed air.

Piston aircraft, some turboprops and aircraft with electric turbine starters may use an approved external source to supply starter current. A unit intended only for continuous avionics power may not tolerate the much higher cranking load, and some aircraft require the onboard battery to remain connected during the start.

Most conventional transport jets use an air-turbine starter. In that arrangement, the GPU can power engine controls, fuel pumps and ignition, but it cannot provide the airflow that initially rotates the engine. The air must come from an APU, another running engine or a separate unit; see our explanation of how an air-start unit supplies pneumatic starting air.

Even on an aircraft with electric starters, external starting is permitted only if the approved procedure allows it and the source can handle the demand. “GPU connected” should never be treated as blanket authorisation to crank an engine.

How do you use an aircraft GPU in a flight simulator?

In a flight simulator, requesting or displaying the GPU and connecting it to the aircraft’s electrical buses are usually separate actions. Higher-fidelity aircraft commonly use this sequence:

1. Secure the simulated aircraft. Set the parking brake or chocks and configure the engines, beacon and doors as required by the add-on’s ground-service logic.
2. Request external power. Use the aircraft tablet, electronic flight bag, ground-services panel or supported service add-on.
3. Wait for availability. Confirm an indication such as EXT PWR AVAIL; the appearance of a cart alone is not enough.
4. Put it on the buses. Select EXT PWR, GRD PWR or the aircraft-specific equivalent.
5. Check the electrical page. Verify that the external-power contactor is closed and the expected AC or DC buses, displays and service loads are energised.
6. Establish another source before removal. Start the APU or engines, connect the appropriate generator, confirm the bus transfer and only then release the GPU.

Simplified aircraft may apply external power automatically, while detailed add-ons may require the battery or a control bus to be configured before the external-power contactor can close. Our simulator-focused A320 electrical-system walkthrough shows how availability, contactors and bus transfers fit together.

Why is the GPU connected but the cockpit still dark?

A mistake we see repeatedly is treating the visible ground cart as proof that the aircraft is powered. Use the indication and electrical synoptic rather than the ramp model.

If a ground-service add-on is controlling the cart, its request state can be separate from the aircraft’s electrical logic. Our guide to requesting and coordinating ground services in GSX explains that side of the process.