It's called a tailslide. It's more risky than straight and level flight...
I have seen Sean Tucker perform that stunt and get to over 100 MPH backwards. His shows are breathtaking (literally). He does a tailslide at around 1:40 in this video and a truly impressive one again at around 3:20 (might be the same one, from a different angle). You can tell he's going backward as he falls through his smoke.