I found AS further maths (OCR) very useful because we covered complex numbers and matrices which are pretty much found everywhere in engineering, so when it came to covering those topics in our lectures it was good to know the basics before they extended them beyond A level. They go pretty fast through subject matter at university level. With complex numbers for example we spent 5 lectures on it, less than a weeks worth of maths at college!
I have found that anything from my A levels that helps you to understand a topic quicker or easier then allows you to direct some more focus onto some of the harder topics.
Personally I have found my course very challenging and intense, but those sentiments are shared by pretty much all of my classmates. One of the first things my fluids lecturer said to the class was “I want to take you to the top of the world, there is no reason why we cannot be as good if not better than MIT or Cambridge". You probably know that aeronautical engineering has many different areas, so in a way it’s quite broad which is an aspect I enjoy a lot.