Which of the following is a characteristic of the APU electrical system?

The characteristic that the APU can power the entire airplane on the ground highlights its role as an auxiliary power source. The APU (Auxiliary Power Unit) is designed to generate electrical power and provide pneumatic pressure for starting the engines and for other needs while the aircraft is on the ground. This feature is particularly useful when the aircraft is not connected to ground power, as it allows for the operation of essential systems, including lighting, avionics, and air conditioning.

Using the APU in this way ensures that the aircraft systems can remain functional without reliance on external sources, which is critical for safety and operational efficiency during pre-flight preparations or maintenance checks. This capability is key in various scenarios, particularly at airports where ground power availability may be limited or where operators prefer to use the APU for convenience.