Because Hong Kong airport is now building a bridge that will connect the North Satellite Terminal with Terminal 1 directly and the current 500s gate number would make those gates appears as out of order, the airport authority is now planning to renumber some gates to make signs clearer.
First of all, existing gate number 15-22 will be renumbered as gate 5-22 in the next month March 28 to free up those numbers
And then in the second phase, existing North Satellite Terminal gates 501-510 will be renumbered as 13-22 in 2020Q2. (Ot will skip number 14 and the current gate 507 will no longer exists because that's where the gate will be)

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