What is the least stable aerial device operating position?

The choice of positioning an aerial device perpendicular to the chassis on a horizontal plane represents the least stable operating position due to the dynamics involved in load distribution and support during operation. When an aerial ladder or platform is positioned this way, it places significant leverage against the chassis, resulting in a higher center of gravity and making the device more susceptible to tipping, especially under lateral forces such as wind or during rescue operations.

In contrast, other positions, such as diagonal or parallel to the chassis, provide better stability by distributing weight and forces more evenly. A diagonal position allows for a more balanced configuration, enhancing the device's stability. Likewise, a parallel position aligns the aerial device with the weight distribution of the vehicle, further mitigating the risk of tipping. An aerial device at an angle to the ground still maintains more contact with the support surface, which helps to maintain stability compared to a perpendicular position. These factors collectively make the perpendicular to the chassis on a horizontal plane the least stable operating position.