Your old aircraft is way too loaded and you are loosing altitude. You'll have to make sacrifices and ditch some of your shipload overboard. If you aim at the islands you'll have less freight cost at your expense.

KEYBOARD: WASD or ⬅⬆➡ to move

Press E to interact/leave the cockpit

GAMEPAD: left stick to move A(xbox)/X(ps4) to interact/leave the cockpit