Convert Km in feet. A basic rule of thumb is to dive feet by 3 to get meter so 30.000 ft divided by 3 is around 10.000 m so 10 km (I know it is a round up). You can use it to convert km into feet. So 2.5 km is around 2500 m multiply by 3 is around 7.500 ft. Fly around 8.000 vertically and you should be out of AAA firing range.
If you want a perfect convertion simply use the right value 1 ft = 12 in = 30.48 cm