See "Romeo Alpha Delta" for more detail. This trophy isn't too difficult once you get the hang of the game. This must be done in one attempt as it's not cumulative.
You will have to fly for 5 kms in one game. This means just in one run. Try to use as many vehicles as you can, buy some revives from the store and try your best not to die. To help make things easier, also buy some gadgets and utilities:
Dezapinator- for 6,500 coins it can randomly disables nearby zappers
Missile Jammer for 5,000 makes random missiles detonate by itself, rendering them harmless
Ezy-Dodge Missiles- for 5,500 makes missiles move slower, therefore making it easier to dodge and avoid them
(you can only apply 2 at a time, so take your pick)
And utilities (I would encourage not to use this as they cost a lot and are for one use only):
Super Head Start starts you off at the 1500 mark. Buy 1 for 3000 or a pack of 5 for 10,000 coins
Quick Revive revives you when you die. Buy 1 for 10000 or 3 for 25,000 coins.
great help - done 10/12 trophies myself but cant be chewed to grind the money for the gold trophy, and thus have all the utilites needed to get to 5000m although i fluked my way to 4200m once.