What determines the base of stability for an aerial apparatus when parked with the aerial device stowed?

The base of stability for an aerial apparatus when parked with the aerial device stowed is determined by the rectangle formed at each corner by the tires. This rectangle is known as the footprint of the vehicle and represents the area that provides support to the apparatus when stationary. The corners of the footprint are critical as they define the points of contact with the ground and establish the overall stability of the vehicle.

A wide and well-defined footprint ensures that the weight distribution is effectively supported, minimizing the risk of tipping or instability. This aspect is essential for aerial devices since they often operate at heights and angles that can amplify any potential shifts in balance. A stable base allows the crew to perform operations safely and efficiently, knowing that the apparatus is secure.

The other factors in the question, such as weight distribution, position of the aerial device, and ground surface angle, are all relevant to overall stability and performance but are secondary to the foundational geometry established by the footprint. Each of these factors can affect how the aerial apparatus behaves in various situations, but none take precedence over the fundamental stability offered by the rectangle formed at the tire corners.