I love flying this aircraft because its a bit quicker than the NGX to get the plane started and in the air, and the FMC is really good. However, I have a problem trying to fly RNAV approaches. Despite the fact that the FMC has numerous RNAV approaches in its database, when I reach the inital fix the FMC immediately deletes the rest of the procedure, attempts to turn towards the runway(but ending up flying S turns) and begins a radical decent to the decision altitude. I have tried RNAV approaches into KATL and KDFW with same problem. Since I have always flown ILS approaches and just started to learn the RNAV system, it is very possible I am doing something wrong. Any suggestions?ThanksStan54