Why didn't Sirius apparate?

[sylviablundell2001]

No: HPFGUIDX 82572

thewierdone18 wrote:
<Like Hogwarts, Azkadan probably has a charm put on it that prohibits 
people from apparating or disapparating>

Damn, damn, damn!! Why have I been making it so difficult for myself 
when the obvious answer is right in front of me?  Of course there's a 
charm on the place.  They'd never be able to keep anyone in there 
otherwise. Some very high-grade wizards are locked up there.
Sylvia (who is reluctant to admit that 12 year-old Tom came up with 
the same solution yesterday)