Speed increase

I am facing problem when i try to decend below 10000ft my speed goes up rapidly my AIR Speed Reaches 250 to 300 when i am close to landing it suddenly happen

does it just jump up, then jump back down?
or does it just strait up increase to 300 without any reason

When i decend i put spoiler on flight i also use VNAV i don’t know why it happens .it increases straight when my speed is 250 prepare to land

is it possible for you to show us a picture?

Use spoilers and slowly put flaps down once you reach certain speeds (usually displayed in cockpit)

What is your vs when u descend?

Set your speed at tod to Mach .66 it’s usually 249 knots and do h The above steps, if it doesn’t work then we will need to find something else

It might be because of your descending VS. If it is too steep then your plane might get faster