Can a Westwind carry more fuel than NGA had on this flight as well as six POB plus equipment without exceeding weight limits? Was the Westwind carrying a maximum load?
Also, I believe the "island reserve" is mandatory for charter flights, but not for "Aerial Work" flights which medivacs usually are. (within Australia)
Maybe this is a case of stretching the equipment to it's limits and having minimum margins.
Maybe another case of having "financial speculators" (managers who have no technical knowledge) who have too much influence on operational matters. The Chief pilot is supposed to sort this out, but he is usually the meat in the sandwich, and has to deal with forces that are much more powerful than he is.
Saving money can destroy aviation companies.