Here's what I found in the newest ANSI A92.2 2009 Standard- these are key safety requirements for utility bucket trucks and other similar aerial devices.
Two new requirements for operator aids are a slope indicator and an outrigger interlock device.
4.5.4 Slope Indicator – An indicator(s) shall be provided that is visible to the operator during setup to show whether the aerial device is positioned within limits permitted by the manufacturer. The allowable limits shall be shown on the unit and in the manual. For units designed for mobile operation such an indicator(s) shall be supplied in the cab.
4.5.5 Outrigger Interlock Device – When an aerial device is equipped with outriggers, and their use is required to pass the stability tests of this standard, an interlock device shall be provided that prevents the boom from being operated from the stowed position until the outriggers have been deployed. Deployment may be sensed when the outriggers meet resistance or by receipt of an indicative response that the outrigger deployment is beyond a predetermined position. The lifting of an outrigger during operation shall not disable boom functions. An interlock override switch may be provided; however, the override mode of operation shall disable automatically.
Note: The operation of outrigger interlocking devices does not assure aerial device stability. It serves only to remind the operator that the outriggers have or have not been deployed. See Section 10.10 (3).