Thoughts...
- Of course people link FR24 data, as it's the only thing usually in the public domain. But yes, it's unreliable being comprised of a merger of data from multiple "amateur" receivers. A lot of that is very good, but I'm not aware of any serious study analysing the data quality available from it; I have heard enough anecdotes from pilots who have seen their aircraft on FR24 particularly at markedly different altitudes to what they knew they were flying at, to distrust it.
- Re: AAIB, yes they can access secondary and even primary radar returns, which are much more informative. But there may be no good reason to. AAIB's job is to provide recommendations that can prevent a future accident. Only they can judge the complexity of investigation needed to achieve that, but often yes - it can be done purely by correspondence. Sometimes not.
- It's a Cirrus, it's full of computers and likely to have a very accurate downloadable flight track. However, the owner and most likely AAIB have that, we don't.
G