What Is the Difference between an Air Start Unit and Ground Power Unit?

Air start units (ASUs) and ground power units (GPUs) are both essential pieces of ground support equipment (GSE) used to assist aircraft between flight operations at an airport or another location. While these units may seem similar based on their names, they serve distinct purposes, each being respectively vital in maintaining efficient and safe flight operations.

As such, understanding their distinctive roles, capabilities, and features is crucial to ensuring proper use. This blog will provide a detailed comparison of ASUs and GPUs to clarify their roles, types, and differences, aiding operators in selecting the right equipment for their specific needs.

What Are Air Start Units?

An air start unit is a form of ground support equipment (GSE) that supplies compressed air to kickstart the engines of an aircraft, providing the force necessary to rotate turbine assemblies and initiate the combustion process. Once the engine is able to sustain its own operations, the air start unit will be disconnected, having finished its task. While ASUs may find use in many situations, they are particularly useful for starting large jet engines in situations where onboard power is insufficient or unavailable.

There are several common types of air start units on the market, each featuring unique design characteristics and capabilities:

Stored Air Cart: This type of ASU stores compressed air in tanks that can be quickly released to start an engine, allowing for rapid operations to be carried out. This makes the stored air cart most popular within smaller ground operations or in locations where electricity may not be readily available.
Gas Turbine Units: These air start units use a small gas turbine engine to produce compressed air. Gas turbine air start units are known for their efficiency, delivering a continuous flow of air that is beneficial for larger or more complex aircraft powerplants.
Diesel Engine Screw Compressor Units: This type of ASU relies on a diesel engine to power a screw compressor, which in turn generates the air flow necessary to start up the powerplant. Diesel engine screw compressor units are quite robust and can be reliably used in environments where electric or gas turbine units might not be practical, such as remote locations or high-altitude airfields.

What Are Ground Power Units?

A ground power unit is a form of equipment that supplies aircraft with electrical power while engines are shut off. While a plane is parked for maintenance, testing, passenger turnover, etc., the ground power units (GPUs) will allow for lights, avionics, air conditioning, and other systems to be operated with ease. GPUs are typically used to avoid draining the aircraft's onboard battery or generator, as well as uphold safety by keeping engines off until the aircraft is ready to leave.

Ground power units come in various configurations, where the choice will generally depend on the power requirements of the aircraft. For example, some are designed with wattage levels that are only suitable for smaller planes, while more advanced or powerful units should be sought out for larger commercial aircraft.

The Differences between ASUs and GPUs

As one can already see, there are clear differences between ASUs and GPUs despite both being ground support equipment. To ensure that you fully understand how these two units are set apart, we will provide a brief overview of common differences:

Downtime: An ASU is only needed during specific moments when starting the engine, while a GPU may be used for hours at a time to provide continuous power. The ability of GPUs to reduce engine use while on the ground helps to cut down on maintenance requirements and fuel consumption.
Fuel Savings: Using a GPU to power electrical systems reduces the need to run an aircraft’s auxiliary power unit (APU) or engines, leading to significant fuel savings. ASUs, by contrast, are typically not operated for long enough to make a major impact on fuel consumption, but they are still crucial in reducing engine wear during start-up.
Safety Risks: Both ASUs and GPUs are designed with safety in mind, but their actual risks differ. Improper use of an ASU could lead to engine damage if the compressed air supply is not correctly regulated, while GPUs must be carefully monitored to prevent electrical overload or overheating. With strict adherence to common safety procedures and manufacturer recommendations for operations, one can ensure optimal functionality and a low risk of hazards.
Maintenance Advantages: ASUs and GPUs both require regular maintenance to uphold proper functionality, but the frequency and scope of the maintenance differ. ASUs generally need thorough inspection of their air delivery mechanisms, while GPUs will need checks for electrical output levels, cooling system performance, and connection health to avoid operational failures.

Where to Purchase Air Start Unit and Ground Power Unit Parts

For those looking to procure air start units, ground power units, or other essential ground support equipment, Zippy Purchasing is your sourcing solution with competitive procurement options offered on over 2 billion in stock listings. Our user-friendly website design and curated product catalogs makes locating desired items simple, and an online Request for Quote (RFQ) service is always available for obtaining information from our staff. Simply submit an RFQ form with details concerning your needs, and a member of our staff will contact you in 15 minutes or less with customized solutions for your consideration.