Hi Musket,
I think you'll find that in reality there's no such thing as Nigerian Cat A. Cat A is based on ICAO Class 1 performance, which basically says that at any time after you start moving with passenegrs on board you can either reject safely, with no damage to anyting, or continue to fly, divert to a safe place to land and do so with no damage to anything. Cat B is basically ICAO Class 2 performance. Everything in Class 1 applies, except it is accepted that there is an acceptable degree of risk during the take off part of flight where, until you reach your defined 'decision point' (refer to my previous post), you may not be able to land safely. However, even if you can't land without damaging your helicopter you can't damage other people, either inside or outside the helicopter. This would mean that you could take off in your 155 on grass in the rainy season, but only class 2 and you have to be sure that when the aircraft digs in to the mud your passengers aren't damaged!
The best references are ICAO performance standards, and NCAR ops for Nigeria.
Hope that helps you.
