When is it permissible to use amateur radio equipment, with or without modification, to transmit outside amateur radio bands?

Amateur radio equipment is designed, built, and authorized strictly for use on allocated amateur radio frequency bands. Because amateurs are allowed to build and modify their own gear, amateur transceivers are not subjected to the strict type-certification required for commercial, marine, aviation, or land-mobile radios. Therefore, it is never permissible to use amateur radio equipment to transmit outside of the amateur bands. Even if you hold an Advanced Qualification or modify the radio, the equipment itself lacks the necessary commercial certification to legally transmit on those outside frequencies.