@nigegilb, who wishes to confirm whether PAPIs were operational...
...apart from public announcements (from NTSB, I think?) that they were functioning, we have a first-person account from Locked_door on this forum (following link goes to his post, presently #442):
http://www.pprune.org/rumours-news/5...ml#post7927159
who despite using the word "departed" describes a landing on SFO 28L "in a heavy jet", which if I understood correctly occurred "few hours before this tragic accident." Locked_door's account includes seeing the PAPI lights (and indeed, noting that they indicated that his/her ship was too high).
Perhaps Locked_door will provide more information to clarify approximately what time his/her approach and landing took place, with the aid of visual guidance from the PAPIs.