What Is the Purpose of the Hole Located on the Tail of Many Commercial Aircraft

When observing commercial airplanes, you might notice a small hole located on the tail of the aircraft airframe. While seemingly insignificant in the grand scheme of an aircraft, this feature plays a critical role in modern aviation operations as it relates to a crucial piece of equipment known as the Auxiliary Power Unit, or APU. The APU is an essential component of an aircraft, providing several key functions that contribute to the safety, comfort, and overall performance of commercial flights. As such, read on as we discuss how APUs benefit commercial aircraft and the relationship between the APU and the holes present on tail assemblies.

The primary purpose of the Auxiliary Power Unit is to supply power to an aircraft when the main engines are not running. This capability is particularly important when the aircraft is on the ground, either when it is parked at the gate or during maintenance. Between flights, the APU will often be used to generate electricity for the aircraft’s electrical systems to ensure that the cabin remains comfortable and operational for passengers as they board. During this time, the APU powers lighting, air conditioning, and other vital systems, making it possible for passengers and crew to enjoy a pleasant environment before the main engines are started.

The APU is strategically located in the tail section of the aircraft, as this position isolates the unit from the main cabin and cargo areas, reducing noise and potential hazards. The design of the aircraft tail also incorporates the ventilation and exhaust systems that are necessary for the APU to operate effectively and safely. In fact, the small hole you see on the tail serves as the exhaust outlet for the APU, allowing it to expel gasses generated during operation.

In addition to providing electrical power, the APU is responsible for supplying air pressure to start the aircraft's main engines. Starting jet engines requires a significant amount of air pressure to initiate the combustion process, a result of requiring optimal fuel-and-air mixtures to generate the thrust and power necessary for flight. Without the APU, the process of starting the main engines would be more cumbersome and time-consuming, particularly in situations where ground-based power and air sources are unavailable.

The Auxiliary Power Unit is also a critical backup system in the event of an emergency. If the main engines fail or if there is a loss of power during flight, the APU can provide essential electrical power to maintain crucial flight systems. This redundancy enhances the safety of commercial airplanes, ensuring that pilots have the necessary tools to navigate and communicate even in adverse conditions.

Beyond its functional roles, the APU contributes to the environmental efficiency of commercial aviation. By providing power while the aircraft is on the ground, the APU reduces the need to run the main engines. This reduction in engine usage leads to lower fuel consumption and decreased emissions, supporting the aviation industry's efforts to minimize its environmental impact. It also translates to cost savings for airlines, as less fuel is required during ground operations.