I;m not sure what IB
Math is but this sounds primarily like a statistics project. You'll probably want to start by getting the raw data (# of types, # of accidents, total number of aircraft, etc). It would probably be best to limit the scope by focusing on just USA airlines or the world's 20 largest airlines or something like that. Also, you should convert # of accidents into #of accidents per hours flown or something like that. That way, the numbers will be more fair. Smaller airlines will have a smaller number of accidents but probably a similar number of accidents per hour flown.
After you get all the fun data, you'll need to run some statistical analysis on it. Excel should do just fine for the level of work you're doing. You'll want to plot a graph in Excel (I think they call it an x-y plot or something like that) If there is a correlation between # of fleet types and # of accidents, there data will fall in a nice line with little scatter. There is an option in Excel where you can get the equation of the line of best fit.
If you need any other help, feel free to send me an e-mail via my profile. I have a college degree in math and am more than willing to help.
Semper ubi sub ubi.