Originally Posted by sandrich

Not that it matters, and I may be completely wrong here but, perhaps you're thinking of the prop brake option? I don't think theres an available APU for the Saab, due to the location of the outflow valves, but there is a prop brake you can install on No. 2, allowing you to run the engine as an APU without the propellor spinning (similar to Hotel mode on ATRs). I hear they are quite cheap, easy to install, and light, but they require careful use because they wear down and become useless very easily... Still would be nice to have when IAD parks us at the only 2 gates that don't have a working PCA unit.