The O2 system in the Kingair "Ghost Flight" aircraft, VH-SKC, was installed new in July 1987 (when the aircraft came on the Australian register, previously RP-C200) and religiously maintained until at least the mid 1990's when it was sold. I don't recall details, but as the aircraft was a very early serial number, I seem to recal the O2 system was manually armed and manually activated and as a result the aircraft limited to FL240.