Strange air incident today

hi, ive registered here to try and get some help on an incident that i viewed today.

I was driving to pick my son up from school and i glanced up to the sky to my right and saw a large jumbo sized plane in an almost vertical nosedive,it was a similar type of dive that ive seen planes do when they are trying to replicate zero gravity.

but the plane in question was one of these radar type planes with the mushroom type of device on top so i doubt it was attempting the gravity thing.

this plane was approx. 5 miles from me and i was almost certain that a crash was about to happen,it went out of veiw and i had to park up and cross the road on foot to go through some bushes to try to see what happened.

half expecting to see an explosion i got though the bushes to see the plane flying at a very low height but horizontaly as it should of been.

sorry to bother you guys but can anyone explain what may have happened as its troubled me all day that i may have witnessed a near miss of some type