Occasionally emergency helicopters land on Hydra, and you can hire a helicopter to bring you to the island from AIA. However the operator will have to obtain specific permission from the local authorities on the island to land. If you want to get to Hydra in the shortest amount of time possible (about 20 mins flying time) you can book a helicopter (depends on time of day as to whether you can land on Hydra or have to put in at Porto Heli on the mainland and then get a water taxi across to the island), but you need to add a couple of thousand Euros to your holiday costs. Please visit Windmill Street Travel for more info and reservations.