The likely cause of the accident involving AVM Brook was anoxia. He had been briefed for a climb to 40,000ft but crashed 20 minutes after take off and the oxygen system was set to ‘Normal’ and not ‘High Flow’ as it should have been. It was also thought that the pressurisation had failed, or the pilot had failed to pressurise before the climb, as with normal oxygen and pressurisation it is unlikely that he would have been rendered unconscious.