With Ansett, on the 146 from Learmonth to Christmas Island, we would work out a PNR back to Learmonth (or, if needs be a Last Point of Safe Diversion to Java) for Depressurised, One Engine out and two engines out and mark the most limiting of those. Before that point we would check the latest weather report from the Christmas Island observer on HF and make a commit decision.
Still occasionally came a cropper with the cap cloud which forms over the Island though - which required some unusual circuits to get onto the runway.
