You need a valid account to fly online on HTC's servers, so the answer is it's only open to those with accounts at the time of the event. It's open to everyone, you would just have to pay for an account for the duration of the scenario to be able to fly it. It's a smokin' deal.

These kind of big events is where some of the best value come from your $30/mo. With all the additional resources something like this takes, there is no way HTC could open these events up to non-customers.
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Sean "Lephturn" Conrad - Aces High Chief Trainer
A proud member of the mighty Flying Pigs
http://www.flyingpigs.comCheck out
Lephturn's Aerodrome for AH articles and training info!