Hawker Beechcraft Beechjet 400A: Aircraft Ground Power Units (GPU)

A ground power unit (GPU) is an essential piece of aircraft ground support equipment that supplies external electrical power to an aircraft while it’s parked on the ground. GPUs keep critical onboard systems – such as avionics, lighting, and air conditioning – operational without requiring the engines or auxiliary power unit (APU) to run. They help conserve fuel, reduce engine wear, and ensure that maintenance crews and flight teams can perform preflight checks and servicing safely and efficiently.

An auxiliary power unit (APU) is an onboard turbine engine that provides power and air conditioning when the main engines are off. A GPU, on the other hand, is an external power source that connects to the aircraft while it’s parked. APUs consume jet fuel and are specific to each aircraft, while GPUs are portable, energy-efficient, and capable of serving multiple aircraft types. Using a GPU helps minimize fuel costs, reduce emissions, and extend the lifespan of the APU.

Aircraft GPUs are designed to deliver the same electrical output used by onboard systems. Common configurations include 400 Hz AC power for commercial and business aircraft and 28V DC or 12V/14V DC power for smaller general aviation aircraft. These outputs ensure compatibility with avionics, lighting, and environmental control systems, supporting everything from maintenance operations to engine starts.

Yes. Aircraft ground power units are available in multiple voltage and frequency options to accommodate the various electrical systems of different aircraft. DC GPUs (12V, 14V, or 28V) are commonly used for piston and turboprop aircraft, while AC GPUs (115V, 400 Hz) are suited for commercial airliners and corporate jets. Many models feature adjustable output settings or interchangeable connectors, ensuring safe and reliable operation across various aircraft types.

Aircraft GPUs can be powered by fuel engines, solid-state electrical systems, or rechargeable batteries. Diesel- and gasoline-powered GPUs offer high-performance capabilities for remote or heavy-duty operations. Solid-state units convert AC input power into stable aircraft-ready output for hangars or fixed installations, while battery-powered GPUs offer quiet, zero-emission operation ideal for indoor or noise-sensitive environments. Each type is designed to support specific ground handling and maintenance requirements.

Fixed GPUs are permanently installed at hangars or gates and draw power from local electrical infrastructure, making them ideal for frequent, high-volume operations. Mobile GPUs, on the other hand, are mounted on carts or trailers, providing flexibility to service multiple aircraft across ramps and aprons. Each type delivers reliable power – selection depends on whether your operations are centralized or require mobility across the airfield.

By supplying reliable external power, GPUs enable preflight activities such as powering avionics, lighting, and environmental systems without relying on the APU or main engines. Ground crews can perform safety checks, refueling, and cleaning while maintaining a comfortable cabin environment for passengers and crew. This efficiency reduces idle time, saves fuel, and speeds up the overall turnaround process, particularly for busy flight schedules.

During maintenance or inspections, GPUs supply stable electrical power for testing avionics, lighting, cabin systems, and engine instruments. This eliminates the need to start the engines or rely on onboard batteries, improving safety and reducing wear. Technicians can also perform software updates, hydraulic tests, and electrical diagnostics efficiently using external ground power, ensuring accurate results and minimizing downtime.

Yes. Many portable and cart-mounted DC GPUs are designed to support engine starts for piston and turbine aircraft. These units provide a controlled power boost that helps start engines quickly without overloading the aircraft battery. This function is especially useful in cold conditions or when an aircraft’s onboard battery is low, ensuring smooth, dependable startup performance.

GPUs are frequently used during pilot training to power aircraft systems and simulators without draining onboard batteries. They allow trainees to practice preflight procedures, instrument checks, and system startups in a controlled, powered environment. This not only conserves aircraft resources but also provides a realistic training experience for pilots in both classroom and hangar settings.

Modern GPUs are designed with multiple safety features to protect aircraft systems and personnel. These include overvoltage and undervoltage protection, frequency regulation, ground fault detection, and automatic power shutoff in the event of irregularities. Such safeguards prevent electrical surges, reduce shock risks, and ensure consistent, stable output – protecting sensitive avionics and maintaining operational safety on the ramp or in the hangar.

Using a GPU instead of an aircraft’s APU significantly reduces fuel consumption and emissions. Because electric and battery-powered GPUs draw power from clean, efficient sources, they minimize the environmental impact of ground operations. They also reduce noise pollution and help airports meet sustainability and emissions compliance goals, making them a responsible choice for modern flight operations.

Routine maintenance includes inspecting cables, connectors, and output terminals for damage; checking voltage and frequency calibration; and replacing filters or fluids in fuel-powered models. Keeping the GPU clean, dry, and properly serviced ensures consistent performance and prolongs its operational life. Following the manufacturer’s maintenance schedule helps prevent unexpected downtime and preserves safety compliance.

Selecting the right GPU depends on your aircraft’s voltage and frequency requirements, power consumption, and operating environment. For example, business jets may require a 400 Hz AC unit, while smaller piston aircraft typically use 28V DC power. PJi offers expert guidance to help match your aircraft with the most efficient GPU for your operational needs – whether for hangar use, ramp service, or mobile deployment.