What Is The Important Purpose Of An Auxiliary Unit In Aircraft?
The power unit is separate from the main engines and allows additional systems to run while the engines are off. Although aircraft can function without APUs, they offer many benefits in flight, and pilots should consider all of the functions that an APU can provide for their aircraft. This blog will cover the many systems that can rely on electric power and the ways this assists the engines in flight.
Auxiliary power units generate power that aids the engines from the start. They work by bleeding air to the engines to initiate them, which eliminates the need for ground systems to power up air conditioning and other electric systems. Even after engines are running, APUs still provide electrical power across the aircraft, allowing the aircraft to independently manage both primary and secondary systems.
One component of an APU is a compressor that functions to draw high-pressure air, or bleed air, to not only power an engine, but to drive the Environmental Control System (ECS). This system monitors air supply, thermal control, and cabin pressurization in aircraft, maintaining the internal environment of the plane. Bleed air from the APU compressor can also power smoke detection systems, fire suppression systems, and avionics cooling processes. All of this can be done in flight thanks to APUs eliminating the need to be grounded to receive additional power.
Additionally, being an in-flight power source, the APU is available onboard at all times, so it can take over in the situation of engine failure. In this case, the APU can provide enough power and air pressure to reignite any of the aircraft’s main engines in the air. For this reason, large and commercial aircraft should always have an auxiliary generator on board as a safety precaution, especially for those flying on non-ETOPS routes.
Aircraft can function without APUs, and some jet engines opt not to rely on a backup generator as it adds extra weight to the flight; however, this heavily limits the aircraft's operating abilities. First, these aircraft must rely on ground power supplies to start their engines and, therefore, the other electric systems that typically receive the bleed air. This leads to higher fuel consumption and costs for airlines, as well as extra engine maintenance due to increased usage. In flight, greater issues present for aircraft without APUs because engine failure would force these aircraft to fly with a single engine, which is only reasonable for small planes.
APUs are stored in the tail cone of aircraft, with the exhaust either next to the unit or at the rear. While these power units can range from high prices of $7,000 to $12,000, they greatly improve the overall function of aircraft operations. Their functions also improve comfortability and safety for passengers, which increases profits and competitive advantages for airlines that utilize APUs. The prices are often justified by the ROI, and usage is simple and efficient. They consume less fuel than engines and can be shut down at any time during flight, making them easy to manage as well as cost-efficient.
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