Apparently (I’m relying on facts from Claude here), aviation uses about 100 billion gallons of oil a year and coconuts yield about 250 gal/acre, so assuming you can approximately replace them 1:1, you would need to plant about 400 million acres under coconut plantation, an area the size of Mexico.

Edit: you don’t have to plant all of Mexico, every percent of fuel you replace is the equivalent of a percentage of a country under a single crop, displacing what would have been there before (presumably some kind of food).