isnt it said that ufos have force fields and will reflect any impact toward that machine. So if ufos do have force fields then how was pilots being crashed into the ufos and both of them dieing. Can our man made aircraft stand against there force field.

I do not know for sure if UFO's have a force field as a means of protection. I'm not sure if there has been any verified cases of one of our aircraft colliding with a UFO causing both crafts to crash resulting in the deaths of any or all occupants.
However, any one can create a forcefield for themselves at very little cost.
Purchase two simple magnets and attempt to push them together incorporating the same poles; North to North or South to South. You will then experience the effect of a simple forcefield.
Imagine if this experiment was magnified by using larger, electro-magnets. The effect would be far greater and multiplied many times. Perhaps someone who is a student of Electromagnetics could expand on this idea.
If UFO's rely on a form of ElectroMagnetics as a source of power I suppose it is quite feasible for them to incorporate a forcefield in their construction.