Extremely high g-forces in impact analysis-abaqus explicit

Hi,
I have modeled a crash analysis of an Unmanned air vehicle on a rigid ground in abaqus explicit. I took the vertical velocity of the UAV as 700 mm/s (0.7 m/s) and the horizontal velocity 12000 mm/s. I want to find the g-force at the point of impact as soon as the impact takes place. The problem is when i plotted spatial acceleration vs time graph in abaqus to find out the g-force I am getting deceleration of the order of 0.22x10^9 mm/s^2 at the time of impact and the g-force is 22000 which I am sure is a very high value..i dont know what exactly is the problem..I have plotted spatial acceleration (vertical component-y axis in my case) A2 vs time. Is there any other option for the acceleration or am i making a mistake in taking the units of acceleration in the graph?
I have taken the units while modelling as 
Length-mm
time-s
Mass-Tonne
Density-tonne/mm^3.

Please help

Bharat