A ventilation system includes a breathing apparatus which provides mechanical ventilation to a patient. The breathing apparatus is configured to perform an automated full recruitment manoeuvre, FRM, comprising a recruitment phase and a PEEP titration phase. In the PEEP titration phase the breathing apparatus is configured to gradually decrease the level of PEEP and to deliver a number of breaths at each of a plurality of PEEP levels, monitor at least one parameter from which an optimal PEEP of the patient may be determined, predict whether the optimal PEEP will be possible to reliably determine later on during the PEEP titration phase, and automatically abort the FRM manoeuvre if it is predicted that it will not be possible to reliably determine the optimal PEEP.