What conditions enable RuBisCO to function as an oxygenase?

What conditions enable RuBisCO to function as an oxygenase? Explain the ensuring process.

Carboxylation is the most crucial step of the Calvin cycle, where COa is utilised for the
carboxylation of RuBP. This reaction is catalysed hy the enzyme RuBP carboxylase, which results in the formation of two molecules of 3-PGA. Since, this enzyme also has an oxygenation activity, it, would be more correct to call it RuBP carboxylase oxygenase or RuBisCO.