"Certified" to be used and ABLE to be used are 2 different concepts.
I've been off the Classic for a few years, but I suspect a savvy FE could figure out how to get the APU and APU generators on line if he had to. Of course, if it didn't work, the battery charge just went WAY down...
Reasonable altitude to prevent overheat on start, possibly a ground-sensing switch or CB or 2...