chippy63;
Our Trent RB211 installation on the A330 uses EPR to set power. EPR is a ratio of pressures between engine internal pressures and outside atmospheric pressure and so is dependant upon a number of varying conditions in both, but an associated N1 reading on approach would around 51 to 55% depending upon weight, flap setting and to a tiny degree, headwind. A very light aircraft (330) on approach, (160,000kg), might see 45 to 50% N1....all very rough figures.