Linear theory, model ions-density profiles and MSIS neutral thermospheric predictions are used to investigaste the stability of the auroral, topside ionosphere to oxygen cyclotron waves; variations of the critical height, above which the plasma is unstable, with field-aligned current, thermal ion density and exospheric temperature are considered. In addition: probabilities are assessed that interactions with neutral atomic gases prevent 0+ ions from escaping into the magnetosphere after they have been transversely accelerad by these waves. The two studies are combined to give a rough estimate of the total 0+ escape flux as a function of the field-aligned current density for an assumed rise in the perpendicular ion temperature. Charge exchange with neutral oxygen, not hydrogen, is shown to be the principle limitation to the escape of 0+ ions, which occurs when the waves are driven unstable down to low altitudes. It is found that the largest observed field-aligned current densities can heat a maximum of about 5¿10140+ ions m-2 to a threshold above which they are subsequently able to escape into the magnetosphee in the following 500s. Averaged over this period, this would constitute a flux of 1012 m-2 s-1 and in steady-state the peak outflow would then be limited to about 1013 m-2 s- by frictional drag on thermal 0+ at lower altitudes. Maximum escapes is at low plasma density unless the 0+ scale height is very large. The outflow decreases with decreasing field-aligned current density and, to a lesser extent, with increasing exospheric temperature. Upward flowing ion events are evaluated as a source of 0+ ions for the magnetosphere and as an explanation of the observed solar cycle variation of ring current 0+ of abundance.