Is the concept of ''starvation mode'' just a myth? for example if a 1440 bmr wanted to lose 2 lbs per wk would it be safe to eat only 990 cal a day?

yes: That's exactly what you want to do: eat about 500 cal/day less than bmr! you can improve your weight loss by exercising each day: this will help prevent you from metabolizing muscle in preference to fat and will also increase your daily caloric need so that, at 990 cal/day, you'll have a larger deficit. It also reduced appetite and is beneficial psychologically.