Is it difficult to publish a paper in the American Institute of Aeronautics and Astronautics Journal?

I am not sure what difficult means. The paper acceptance rate/ratio in recent years can be obtained by writing to AIAA. So write to them. A few years back, 40 percent acceptance rate was the figure I recall. Is that difficult or easy? Publication is a combination of paper quality, luck (i.e., review process), paper subject wrt current research interest, paper subject wrt advances in understanding the fundamentals, and there is also a presentation element I suppose.

Be prepared to be patient - looks like it takes a while. Just seeing the latest issue, many of the articles were submitted over a year ago, some even 18 months or more.