The Dodo seaplane is an exclusive vehicle in GTA 5, which appears as a Random Event after you complete the Nervous Ron mission with Trevor.
The Random Event is found in the sea cove east of Ron Alternatives Wind Farm. You'll need to approach on a boat or sea faring vehicle to trigger the event - jet skis are available from the beach a little further down the coast to the south.
Once the marker appears, head into the cove and shoot the gunmen in the boats before hopping into the Dodo.
As you leave the area two more boats of gunmen will attack, but you can simply fly away and leave them behind. Once completed, the Dodo seaplane will spawn in the following two locations:
At the dock on the small Vinewood Hills lake.
At the dock to the north of the Alamo Sea.
There’s also the option to buy the Dodo from the Elitas Travel website for a cool $500,000 once you’ve completed the Random Event.
Looking for more GTA 5 help? Then check out our Grand Theft Auto 5 cheats and guides: everything you need for PS4, Xbox One and PC.