Ground Power Units: Supporting Aircraft While They Are on the Ground

Aircraft depend on electrical power for far more than propulsion. Lighting, cockpit systems, communications, avionics, environmental equipment and maintenance functions can all require electricity while an aircraft is parked. Keeping the aircraft's engines running simply to provide this power would often be inefficient, noisy and unnecessary, which is why dedicated ground-based power equipment plays such an important role in aviation operations.

Ground Power Units provide aircraft with an external source of electrical power while they are parked at an airport, maintenance facility, hangar or other operating location. By connecting an aircraft to an appropriate external supply, essential onboard systems can be operated without relying continuously on the aircraft's engines or auxiliary power unit. This supports maintenance, servicing, passenger operations and preparations for the next flight.

What Is a Ground Power Unit?

A ground power unit, usually abbreviated to GPU, is equipment designed to supply electrical power to an aircraft while it is on the ground.

The unit connects to the aircraft through an appropriate external power connection. Once connected and operating within the required electrical parameters, it can supply energy to compatible onboard systems.

The exact electrical output required depends on the aircraft and application.

This means a GPU must be correctly matched to the electrical characteristics of the aircraft it is intended to support.

Why Aircraft Need External Power

Aircraft can require electricity long before their engines are started.

Pilots and ground crews may need to configure avionics, check instruments, operate lighting and perform pre-flight procedures.

Maintenance technicians may also need electrical systems energised for testing and diagnostics.

Cabin equipment may need power while passengers are boarding or while an aircraft is being prepared between flights.

Providing this electricity externally avoids operating other onboard power sources unnecessarily.

Reducing Dependence on the Auxiliary Power Unit

Many aircraft have an auxiliary power unit, commonly known as an APU.

An APU can provide electrical power and other services independently of the main engines.

However, operating it consumes fuel and generates noise and emissions.

Where suitable ground infrastructure is available, using external electrical power can reduce the amount of time the APU needs to operate while the aircraft is parked.

Fixed and Mobile Ground Power

Ground power equipment can be provided in several configurations.

Fixed systems may be integrated into airport stands, hangars or passenger boarding bridges.

These installations are useful where aircraft regularly occupy established parking positions.

Mobile units provide greater flexibility.

They can be moved between aircraft or positioned wherever electrical support is required, making them useful for maintenance facilities, remote stands and operational environments without permanent infrastructure.

Diesel-Powered GPUs

Some mobile units generate their own electricity using an internal combustion engine connected to a generator.

These systems can operate independently of the airport's electrical infrastructure.

That independence can be valuable at remote locations or where mains electrical supplies are unavailable.

However, fuel-powered equipment introduces considerations including emissions, noise, fuel storage and maintenance.

Battery Ground Power

Battery technology provides another approach.

Battery-powered ground equipment can store electrical energy and deliver it when an aircraft requires support.

This can reduce local exhaust emissions and operating noise compared with engine-driven generation.

However, battery capacity, charging requirements, weight and expected operating duration all need to be considered when selecting such equipment.

Mains-Powered Systems

Where a reliable electrical infrastructure exists, ground power can be produced from the local mains supply using suitable conversion equipment.

This can be particularly appropriate at permanent airport stands and maintenance facilities.

The incoming electricity is converted into the voltage, frequency and current characteristics required by the aircraft.

The design of the conversion system therefore becomes critical to ensuring that the aircraft receives a stable and appropriate supply.

Aircraft Electrical Requirements

Aircraft do not necessarily use the same electrical standards as ordinary buildings.

Different aircraft can require different AC or DC supplies.

Some aviation systems use 400 Hz alternating current rather than the 50 Hz normally associated with UK mains electricity.

DC electrical systems are also used extensively across aviation.

Ground equipment must therefore provide the correct output for the aircraft being connected.

Why 400 Hz Power Is Used

Higher-frequency electrical systems can offer advantages in aviation because certain transformers, motors and other electrical components can be made smaller and lighter.

Weight is extremely important in aircraft design.

This is one reason 400 Hz AC systems became established in many aviation applications.

A ground power system supporting such an aircraft must therefore reproduce the required electrical supply accurately.

Stable Voltage and Frequency

Providing electrical power involves more than simply achieving the correct nominal voltage.

The supply needs to remain within appropriate limits while loads change.

Aircraft systems may switch on and off during servicing, creating changes in electrical demand.

The ground supply needs to respond appropriately while maintaining stable output conditions.

Frequency stability is similarly important for AC equipment.

Power Capacity

Different aircraft have different power requirements.

A small aircraft undergoing maintenance may require substantially less electrical power than a large commercial aircraft preparing for departure.

Ground equipment should therefore be selected according to the maximum expected demand and the characteristics of the connected aircraft.

Using appropriately rated equipment helps prevent overload while ensuring sufficient capacity for normal operations.

Connections and Cables

The physical connection between the ground equipment and aircraft is a critical part of the system.

Cables must be capable of carrying the required electrical load while remaining suitable for repeated handling in an airport environment.

Connectors also need to provide secure electrical contact.

Wear, contamination or physical damage can affect connection quality and should therefore be identified through appropriate inspection and maintenance.

Cable Management

Airport ground areas are busy workplaces containing vehicles, personnel and numerous pieces of servicing equipment.

Poorly positioned electrical cables can create trip hazards or potentially be damaged by vehicles.

Effective cable management therefore contributes to both electrical reliability and ground safety.

Cables should be positioned and handled according to established operating procedures.

Supporting Aircraft Maintenance

Ground power is particularly important during aircraft maintenance.

Technicians may need to energise electrical systems for fault diagnosis without running engines or onboard generating equipment.

Avionics, lighting, control systems and other electrical equipment can then be tested under controlled conditions.

Reliable external power can therefore support both routine maintenance and more complex troubleshooting.

Supporting Turnaround Operations

Commercial aircraft often spend relatively short periods at the gate between flights.

During this turnaround period, numerous activities may occur simultaneously.

Passengers leave and board, baggage is transferred, aircraft systems are checked and the cabin is prepared.

External electrical power allows required aircraft systems to remain operational throughout these processes without unnecessary engine operation.

Environmental Considerations

Airports are increasingly focused on reducing emissions associated with ground operations.

Aircraft engines, APUs and diesel-powered ground equipment can all contribute to local emissions.

Electrified ground infrastructure and battery equipment can help reduce reliance on combustion-powered systems where suitable electrical supplies are available.

The overall environmental benefit depends on factors including the electricity source, equipment efficiency and operating practices.

Noise Reduction

Noise is another consideration around airports and maintenance facilities.

Combustion engines and APUs contribute to the overall acoustic environment.

Electric ground equipment can operate much more quietly.

This can improve working conditions for ground personnel and reduce noise around airport facilities.

Protection and Monitoring

Electrical protection is essential when supplying expensive and safety-critical aircraft systems.

Ground equipment may incorporate monitoring for conditions such as incorrect voltage, frequency abnormalities, overloads or other electrical faults.

If operating conditions move outside acceptable limits, protection systems may disconnect or inhibit the supply.

The precise protection arrangements depend on the equipment and application.

Inspection and Maintenance

Ground electrical equipment itself requires regular maintenance.

Cables, connectors, wheels, controls and electrical systems can all experience wear during repeated use.

Mobile units may also be exposed to weather, vibration and accidental impacts.

Preventative maintenance helps identify deterioration before it results in equipment failure during aircraft operations.

Operator Training

Ground personnel need to understand the correct procedures for connecting and disconnecting external power.

Incorrect operation could damage connectors, cables or aircraft equipment.

Procedures may include checking equipment condition, confirming compatibility, making the connection correctly and coordinating with flight or maintenance crews before energising the supply.

Designing for Operational Reliability

Airport operations depend heavily on equipment availability.

A failed ground power system can disrupt maintenance or aircraft turnaround activities.

Reliability therefore needs to be considered throughout equipment selection, installation and maintenance.

Some facilities may also maintain backup equipment so operations can continue if a primary unit becomes unavailable.

The Wider Move Towards Electrified Ground Support

Ground power forms part of a broader range of airport ground-support equipment.

As airports work to reduce emissions, increasing numbers of ground operations are being electrified.

Power supplies, baggage equipment, aircraft tugs and other ground-support systems may increasingly rely on electrical rather than combustion-based technologies.

Ground electrical infrastructure is therefore likely to become an increasingly important part of airport planning.

Ultimately, Ground Power Units provide the external electricity needed to operate aircraft systems safely and efficiently while aircraft are parked, maintained or prepared for flight. Whether supplied through fixed infrastructure, mobile generators or battery-based equipment, correctly specified ground power can reduce unnecessary engine and APU operation while supporting maintenance, turnaround efficiency, lower noise and increasingly electrified airport operations.