The aerial device is least stable when oriented perpendicular to the truck's longitudinal axis. Which description best matches this orientation?

• A. Perpendicular
• B. Parallel
• C. Diagonal
• D. Aligned

Answer: (A)

Stability for an aerial device hinges on how the boom’s load sits relative to the truck’s base formed by the wheelbase and stabilizers. When the boom is pointed to the side of the truck (perpendicular to its length), the weight and any wind push create a tipping moment that acts across the narrow side-to-side plane of the base. That lateral moment is hardest for the stabilizers to resist, so the margin of stability in this orientation is smallest.

If the boom runs along the truck’s length (parallel), the load stays largely within the stabilizers’ footprint, and the resisting forces can counter the tipping tendency more effectively, giving greater stability. A diagonal orientation would fall somewhere in between, and “aligned” or parallel describes a orientation along the length rather than across it.

So the orientation that matches being perpendicular to the truck’s longitudinal axis is described as perpendicular.