What is Auxiliary Power Unit (APU) Aircraft?
An Auxiliary Power Unit (APU) aircraft is a type of aircraft that is equipped with a self-contained power unit, in addition to the primary engines, to provide an alternate source of power when needed. The primary engines of an aircraft provide power for propulsion, but sometimes the aircraft may need a supplementary source of power to run essential systems such as electronics, lighting, and pneumatics.
History of Auxiliary Power Units
The concept of auxiliary power units (APUs) dates back to the early days of aviation, when pilots were seeking a reliable source of power for starting engines and other critical systems. In the 1920s, manufacturers began to install self-contained power units in some aircraft, which provided electric power for starting the main engines and other accessories.
Over the years, the design and functionality of APUs have evolved, becoming more sophisticated and capable. Modern APUs are used in a wide range of aircraft, from general aviation to commercial airliners and military aircraft.
Function of Auxiliary Power Unit Aircraft
The primary function of an APU is to provide an alternate source of power when the primary engines are not running. This can be in emergency situations, such as a sudden loss of main engine power, or when an engine is being overhauled or replaced. An APU typically runs on a separate fuel tank, which is typically fueled with the same type of fuel as the primary engines.
An APU typically has a number of outputs, including:
- Electrical power for starting the main engines and other accessories
- Compressed air for powering aircraft systems such as the flight control system, brake system, and passenger comfort systems
- Generator output to power electrical systems, including lighting, communications, and navigation equipment
- Pressurization for aircraft pressurization and climate control systems
Advantages of Auxiliary Power Units Aircraft
The benefits of installing an APU on an aircraft are numerous, including:
- Emergency starting: An APU allows an aircraft to be started and taxied off a runway in case of an emergency, increasing the safety of the crew and passengers.
- Reliability: An APU can be used to maintain systems in the event of an engine failure, keeping critical aircraft systems operational.
- Reduced wear and tear: By taking the load off the main engines, an APU can help reduce wear and tear on the engines and aircraft components.
- Cost-effective: APUs are designed to be simple, low-maintenance devices that require minimal maintenance, making them a cost-effective option.
Types of Auxiliary Power Units Aircraft
APUs are used in a variety of aircraft, including:
- Turboprop aircraft: Most turboprop aircraft have a dedicated APU for providing power for essential systems.
- Twin-turbofan aircraft: Many twin-turbofan aircraft have a built-in APU or one can be installed externally.
- Business aircraft: Luxury business aircraft often feature advanced APUs for maximum reliability and comfort.
- Military aircraft: Some military aircraft have built-in APUs for power and quick-start capabilities.
Standards and Certification for Auxiliary Power Units Aircraft
To ensure the safe operation and maintenance of APUs, manufacturers and regulators must meet strict standards and requirements. These include:
- FAA guidelines: The Federal Aviation Administration (FAA) regulates APUs in the United States, setting standards for performance, safety, and environmental impact.
- JAA guidelines: The European Aviation Safety Agency (EASA) sets guidelines for APU design and installation in Europe.
- API guidelines: The API 1160 specification defines requirements for APU systems.
Conclusion
An auxiliary power unit aircraft is an essential component of many aircraft, providing an alternate source of power when the primary engines are not available. With its reliability, simplicity, and low-maintenance design, an APU is an effective means of ensuring the safe operation and maintenance of critical aircraft systems. Whether for general aviation, commercial transport, or military applications, the auxiliary power unit has proven to be a vital asset for pilots and crew worldwide.
