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I’m just wondering about flight planning section, for an alternate aerodrome which one is to choose, For example. If I’m flying from Strahan to king island, which aerodrome more suitable for an alternate, Smith, or Wynyard, Devonport or and George Town. Is it any rules regarding choosing, as I haven’t seen much on the book p3.3
It's up to the pilot to select a suitable alternate. The only thing the AIP has to say about it is that, for it to be a suitable alternate, it must be a suitable destination for the flight and it must not itself require an alternate. (ENR 1.1 para 184.108.40.206)
To be a suitable destination, it must be an aerodrome that would comply with all of the landing requirements that apply to your aircraft and the flight to that aerodrome must not require any irregular operation. In other words, you can't nominate an alternate that would require you to declare an emergency to go there.