When I worked for a USA supplemental air carrier in the early 1980s, we had flights to Diego Garcia, which is a US military base, in the middle of the Indian Ocean. No alternate airport available. The FAR 121 regulations required to have 2 hours of cruise fuel reserve, as minimum fuel requirement.
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I do not know how that applies to you in Australia. I recall having done one charter to Alice Springs, cannot recall how close were the nearest alternates.
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Happy contrais