Aptitude says it all, really. Some people have an innate ability to paint/play musical instruments tunefully / solve complex mathematical problems / understand aerodynamics /understand the workings and design of things mechanical /understand electronics.
Being in sales does not preclude a career in Engineering,on the contrary, the need to be able to communicate andget along with people is a terrific asset.
Have faith in your own abilities, play to your strengths and do a bit of homework to show that you understand the various facets and paths within the sweeping term "Engineer"
take note of the previous 2 posters...they are clued -up, i had a chequered career that included sales and mechanicing as well as bits of machining/fabricating/welding/building work...catering!....but never aero-engineering. (apart from models
)
GOOD LUCK.