Claims or suits that arise out of the ownership, maintenance, or use of aircraft are generally excluded under the standard commercial general liability (CGL) forms. Businesses that elect to use private aircraft in their operations must purchase specialty insurance to cover their aircraft liability loss exposure: aircraft liability coverage or stand-alone non-owned aircraft liability and perhaps excess aircraft liability coverage as well. Coverage for third-party aircraft liability is often provided, which also includes hull (physical damage) and medical payments coverage. Aircraft policies are not standardized and vary widely. Some insurers offer policies that combine aircraft liability and hull with other aviation coverage, such as aircraft products liability, airport liability, land-based general liability, and hangarkeepers liability coverage.