When it comes to aircraft operations, most people focus on what happens in the air. However, a great deal of essential activity occurs on the ground to prepare an aircraft for flight. One critical component of ground support equipment is the Ground Power Unit (GPU). These units provide external electrical power to aircraft while they are parked, undergoing maintenance, or being prepared for departure.
In this article, we’ll explore what ground power units do, why they are essential, and why there is such a diverse range of GPUs available. We’ll also examine the different types of GPUs—start power units, continuous power units, and hybrid or combination units—and how voltage requirements differ depending on aircraft type and usage.
Table of Contents
What is a Ground Power Unit?
A Ground Power Unit (GPU) is a device that supplies electrical power to an aircraft when its engines or Auxiliary Power Unit (APU) are not operating. This external power is vital for running aircraft systems on the ground, such as:
- Cabin lighting
- Avionics
- Air conditioning
- Navigation systems
- Cockpit instruments
- Hydraulic and fuel systems
Without a GPU, aircraft would have to rely on onboard power sources like the APU, which burns fuel, produces noise, and generates emissions. Using a GPU is typically more efficient, environmentally friendly, and cost-effective.
Why Are GPUs Needed?
GPUs are essential for several reasons:
- Environmental impact: APUs are noisy and emit pollutants. Ground power is quieter and cleaner.
- Fuel efficiency: Running an APU consumes jet fuel, whereas a GPU uses electricity or diesel, often at a lower cost.
- Operational readiness: Airlines can keep systems like air conditioning, avionics, and lighting operational without starting the engines.
- Maintenance support: Maintenance crews rely on GPUs to power systems for testing and diagnostics.
Why Are There Different Types of GPUs?
Aircraft come in a wide variety of sizes and power requirements, from small private jets to large commercial airliners and military aircraft. This diversity means that no single power solution fits all.
Different operational needs – such as starting engines, powering onboard systems for extended periods, or providing mobile versus fixed power – require specialised aircraft GPU configurations. This has led to the development of several types of GPUs with varying outputs, capacities, and functionalities.
Types of Ground Power Units
1. Start Power Units (Battery or Boost Packs)
Function:
Start power units are designed to deliver a high burst of current needed to start aircraft engines or APUs. These are typically used when the main battery is insufficient or when the APU is inoperative.
Characteristics:
- Provide very high amperage for short durations.
- Portable—often wheeled units or battery packs.
- Not designed for continuous power supply to onboard systems.
- Rechargeable or powered by an external energy source.
Common Voltages:
- 24V DC – Used primarily for smaller general aviation aircraft and helicopters.
- 28V DC – Standard for many light to mid-size aircraft, both civilian and military.
2. Continuous Power Units (Static or Mobile)
Function:
These GPUs supply stable continuous power for extended ground operations, such as during maintenance, passenger boarding, or pre-flight checks.
Characteristics:
- Available as fixed installations at airports or mobile trailer-mounted units.
- Designed for low ripple, clean power to protect sensitive avionics.
- Can run for hours as needed without interruption.
Common Voltages:
- 28V DC – Common for small to medium aircraft.
- 115V 400Hz AC – Standard for most commercial airliners and military aircraft. The frequency (400Hz) allows for lighter, smaller onboard transformers compared to standard 50Hz or 60Hz power.
- Some large aircraft and military applications require 270V DC, offering more efficient power delivery with lighter wiring.
3. Hybrid and Combination Power Units
Function:
Hybrid units combine the functions of start power and continuous power in a single device. These versatile GPUs can supply high current for engine starts and then switch to continuous power for systems operation.
Characteristics:
- Reduce the need for separate units on the ground.
- Offer flexibility for operators working with diverse aircraft types.
- Often used in remote operations or smaller airfields where space and equipment availability are limited.
Power Capabilities:
- Typically offer both 28V DC start power and continuous power.
- Some models combine 28V DC with 115V 400Hz AC output to service a wider range of aircraft.
Voltage Differences Explained
DC Power (Direct Current)
- 24V/28V DC
- Common for general aviation, business jets, turboprops, and helicopters.
- Used for engine starting, avionics, lighting, and other systems in smaller aircraft.
- 270V DC
- Increasingly used in modern military and larger commercial aircraft.
- Provides higher power with lower current, reducing cable size and weight.
AC Power (Alternating Current)
- 115V 400Hz AC
- The standard for most airliners, regional jets, and military aircraft.
- 400Hz is preferred in aviation due to lighter and smaller transformers and electrical components.
- Variable Frequency AC (VFAC)
- Found in some modern aircraft with variable-speed generators, but GPUs typically provide constant 400Hz to match older systems and standard requirements.
Matching GPUs to Aircraft Types
| Aircraft Type | Common GPU Output | Application |
|---|---|---|
| Light aircraft | 24V / 28V DC | Start and continuous power |
| Business jets | 28V DC / 115V AC 400Hz | Start and cabin/avionics power |
| Commercial airliners | 115V AC 400Hz | Full continuous power on ground |
| Military aircraft | 115V AC 400Hz / 270V DC | Start, continuous, and mission support |
| Helicopters | 28V DC | Start and avionics power |
Conclusion
Ground Power Units are an essential part of airport and maintenance operations. Whether providing a surge of power to start engines or supporting an aircraft’s onboard systems for extended periods, GPUs are crucial for efficiency, safety, and environmental sustainability.
The diversity in GPU types reflects the wide range of aircraft designs and operational needs. From simple 28V DC start packs for small aircraft to sophisticated combination units supplying both AC and DC power for large airliners, the right GPU ensures seamless ground operations.
If you’re involved in aviation operations or ground support, choosing the correct GPU for your fleet is vital—not only for operational efficiency but also for the longevity of your aircraft’s electrical systems.
