Don't know much about NAC, but ALS is a pretty big operation here in Kenya. They have a wide ranging fleet and operate over a wide area of east/west/south Africa and probably north Africa too by now. They specialise in lease work or operating small airlines all over the region. Its a HUGE company here - way bigger than most people realise. Owned and set up by a primarily Asian family I believe - dozens of pilots of all skills and experience levels. I have no actual information but it seems like they have a high turn-over of pilots but they are a stepping stone to Kenya Airways for most pilots - a stop gap between game park Caravan operations and national airline Boeings. Some pilots have been there for ages, others transit through quite quickly. Think some of their terms are a bit tough but it obviously works given the number of pilots heading there. It is a Kenyan company but operates all over so I don't know what their workpermit/nationality requirements are.....