Agusta A109C: 28V DC Aircraft Ground Power Units

A 28V DC aircraft ground power unit (GPU) is a device that supplies external electrical power to an aircraft while it is on the ground. These units provide 28-volt direct current to operate onboard systems, power up avionics, and start engines or auxiliary power units (APUs). Using a GPU reduces the strain on the aircraft’s internal battery and ensures critical systems are operational during maintenance, preflight inspections, or ramp operations. They are essential for keeping aircraft in peak condition without relying on internal power sources.

28V DC GPUs play a vital role in aircraft maintenance by providing a stable power source for diagnostics, software updates, and avionics checks. Without a GPU, technicians would have to rely on the aircraft’s battery, which can degrade over time and may not provide consistent voltage. A GPU ensures safe and efficient maintenance operations by supplying uninterrupted power to systems that need to remain energized during servicing. This contributes to both better maintenance outcomes and reduced battery replacement costs.

Yes, many 28V DC ground power units are specifically designed to deliver high current output for starting piston and turbine engines. This is especially useful during cold weather starts or when the aircraft’s onboard battery is low. By supplying instant and reliable cranking power, the GPU helps minimize engine start delays and reduces wear on the internal electrical system. Models with higher amp output or battery boost capabilities are ideal for frequent engine starts in field conditions.

28V DC GPUs are commonly used with general aviation, business aviation, and military aircraft equipped with 28-volt electrical systems. This includes popular models from Cessna, Piper, Beechcraft, Cirrus, and many light helicopters. They are also used for regional jets and turboprops that require a portable, efficient power source during ground operations. Pilots, maintenance crews, and FBOs rely on 28V GPUs to support routine tasks and maintain aircraft readiness.

28V DC GPUs are available in both electric and engine-driven configurations. Electric models can be powered by single-phase or three-phase AC voltage, making them ideal for hangar use or facilities with dedicated power access. For ramp or off-grid operations, engine-driven GPUs powered by gas or diesel provide the flexibility to deliver mobile power wherever needed. There are also compact battery-powered GPUs that are completely self-contained and ideal for remote or mobile servicing.

A 28V DC GPU provides direct current (DC) power, typically for aircraft systems and engines that require 28 volts. In contrast, AC GPUs deliver alternating current (usually 115V or 400Hz) to support aircraft that operate on AC systems, such as larger commercial jets. DC GPUs are best suited for general aviation, business aircraft, and military applications with DC requirements, while AC GPUs are used for aircraft with more complex electrical needs. Selecting the correct GPU type ensures compatibility and safe operation.

Yes, battery-powered 28V DC GPUs are an excellent solution for quick starts and short-duration power needs. These lightweight, portable units are popular for preflight checks, avionics updates, and field maintenance where access to shore power or fuel-driven units is limited. While they may have shorter runtimes than gas or electric units, they’re incredibly useful for rapid deployment and off-grid scenarios. Start Pac and FoxCart offer well-regarded models in this category.

Modern 28V GPUs often include built-in safety features such as reverse polarity protection, thermal overload protection, voltage regulation, and circuit breakers. These protections help prevent equipment damage, safeguard personnel, and ensure consistent output during operation. Some units also feature soft-start capabilities or current limiters to avoid power surges. Always review the manufacturer’s specs to understand the safety features specific to the unit you’re considering.

Choosing the right 28V DC GPU depends on your aircraft’s power requirements, frequency of use, and operational environment. Consider whether you need a portable battery-powered unit, a hangar-based electric GPU, or a mobile gas/diesel-powered cart. You’ll also want to match the unit’s output (in amps) to your aircraft’s engine start and system load needs. PJi’s aviation specialists are available to help you compare options and select the best solution for your aircraft or fleet.

Absolutely! A 28V GPU provides clean, stable power during avionics software updates, reprogramming, and troubleshooting, which helps avoid interruptions and power-related faults. Using a GPU during these procedures prevents battery drain and ensures the aircraft’s systems remain powered for the duration of the task. This is especially critical during longer update cycles or when running diagnostics on multiple systems.

Many gas or diesel-powered 28V GPUs are designed with rugged, all-weather construction for outdoor use on the ramp. These models typically include weather-resistant enclosures, heavy-duty wheels, and built-in ventilation systems. However, battery-powered or electric GPUs may have environmental limitations depending on the manufacturer. Always follow the equipment's operating guidelines and environmental ratings to ensure safe use in varying conditions.

Routine maintenance for a 28V DC GPU includes inspecting cables and connectors, checking battery condition (if applicable), cleaning air filters, and performing regular diagnostics. Engine-driven models should receive oil changes, fuel filter replacements, and other engine maintenance as recommended by the manufacturer. Keeping the unit clean, dry, and stored in appropriate conditions also helps prolong its service life. Refer to the product manual for detailed service intervals and procedures.

Yes, many helicopters – especially light utility or training models – operate with 28V electrical systems and are fully compatible with 28V GPUs. These units provide reliable startup power and support essential systems on the ground during inspections or training sessions. Be sure to confirm the helicopter’s electrical requirements and connector compatibility before selecting a unit. PJi can assist in verifying compatibility for your specific rotorcraft model.