Abstract: A mobile aerial device, which also has deployable outriggers, has sensors for the outrigger-supported weight, sensors for boom azimuth, elevation and extension, and sensors for other boom conditions. An on-board digital computer is programmed with load tables for the device. The various sensor signals and load table data are computer-processed to determine the approach of tipping or overload conditions. When operating near a dangerous obstacle which it is desired to avoid, the boom is initially caused to assume certain preparatory positions relative to the obstacle and data are computer-generated which extrapolate from these positions a region in space which represents a prohibitively close approach of the boom to the obstacle. The foregoing information is used to alert the operator to the approach of a dangerous condition and also to prevent the crane from performing movements which could cause tipping or which would encroach upon the prohibited region.