What is an APU Used for in an Aircraft?

You may have noticed the hole at the tail end of an aircraft, that of which is the exhaust outlet for the APU. An APU is a unique device that operates similarly to other engines on the plane but does not play any role in propulsion. Instead, the APU takes on two very important jobs: helping the plane initiate its startup sequence and providing a backup power source in the event of engine failure. Auxiliary power units were used in aircraft as early as World War I to power radio transmitters and help drive the onboard DC generators. Today, APUs are found on nearly every commercial aircraft, and unlike other systems, the vast majority of APU components are manufactured by giants like Honeywell and Boeing.
 
The APU mostly functions like any other engine on an aircraft in that it combusts a fuel-air mixture to generate power output. The difference, however, is that the output can be used to power various electrical systems on the plane. Additionally, some compressed air from the APU is donated to aid in helping start the main engine. The APU is situated at the back of the aircraft due to the limited real estate elsewhere on the plane. Even with the APU's distance from the main engines, the compressed air has such high pressure that it has no problem reaching its destination.
 
Besides the startup sequence and taxiing, the APU will generally remain off during the entire flight. In addition to providing compressed air to the engines, the APU also powers the cabin lights and avionics systems prior to takeoff. When the system is engaged, panels on both ends of the fuselage will open up and allow air intake. After combustion, the exhaust will exit out the hole in the back of the aircraft.
 
Aside from its role in the engine startup procedure and pre-takeoff power supply, the APU serves the extremely important function of providing a backup power source in the case of generator failure. For example, if one or more generators were to fail during flight, the captain could activate the APU to provide limited auxiliary power. In fact, many experienced pilots will engage this system immediately after recognizing a generator malfunction. Additionally, if a pneumatic malfunction were to occur in the main engines, the APU can provide compressed air for cabin pressurization.
 
Clearly, the APU plays a critical role in aircraft safety. If you are in the market for any aircraft component, ASAP Logistic Solutions has made the process streamlined and cost-effective. We are owned and operated by the well-known ASAP Semiconductor, and as such, have access to an inventory of over 2 billion new, obsolete, and hard-to-find aerospace parts. Furthermore, we operate with AS9120B, ISO 9001:2015 certification, and FAA AC 00-56B accreditation which means you can always rely on the integrity of the products we distribute. In addition, we have access to a robust international supply chain which allows us to offer expedited shipping on most items. For customers facing AOG situations, our team members are available whenever to discuss possible same-day shipping on select in-stock items. Finally, as we believe in responsible sourcing, we are the only independent distributor to offer a No-China Sourcing pledge. Please browse our inventory today and submit an RFQ to receive a personalized quote in 15 minutes or less.