Oh. Not good.
So, looks like TCPIP is up and running so you are pretty far along in the boot. A control-c/spam enter a few times might get you to a login prompt, if you time it between the messages printed to console.

If you do manage to get in, you will likely be spammed with all the happy fun AIX stuff it prints to console. I think in 5.3 TL7?? There's the swcons command, you could do a swcons /tmp/console.out to temporally send all messages printed to console to file. To revert it back just typing swcons.
If you have telnet/ssh it might be responsive on the network. Not sure however.
So, was this lpar part of a cluster?

Next lets go talk about single user mode!
Also, do you have any sort of HMC or is this a standalone frame?

If standalone, this should work (again 5.2 not my cup of tea). Lets bring this lpar up in single user mode. With your console still attached, bounce the lpar (nicely if hmc, or well...press the magical power button if you must). You should see the system start to IPL, and if you are sitting near it, it should beep on the frame (if so equipped) and beep/flash your console. Alternate, if you have a monitor/kbd hooked up it would likely flash/beep there so yeah.
Now, you should see an option of choosing another boot list during the time of the beeping/flashing. Should be boot selection. An option for 'Press 6 to start diagnostics'.
Normal AIX boot header of 'Welcome to AIX' will display, and you will be presented with a diagnostic screen which you can enter past. The next screen should have an option for Start Shell, or Single User mode.


IBM has some good docs about what can and cannot be done in that mode and how to exit single user and get into multiuser. Here's one now! IBM Booting AIX in Single-User Mode
From there, I can't say which commands will work and which wont. I only had to go into single user mode once for a really messed up inittab issue that a vendor left me with!


Again I could be way off the processes as I have 6.1 and 7.1 under my belt. The 5.3 systems and our lowly 4.3.3 box was retired as I came in.

Anyways, do you have other backups of this lpar?
Good news, it sounds like your filesystems are protected if they are on SAN, you just need to get to a point where you can bring them in.
Bad news, depending on if any excludes were done you may end up with a painful rebuild, if other data wasn't backed up via other means.

If you have the knowledge base of 5.2, I'd really look at setting up a mirrored rootvg once you are up and running. I've done both a local hdisk0 and a SAN provided hdisk1 as a mirror before with 6.1 TL7. Not sure if applicable with 5.2, I know a lot of things have changed.

Unfortunately a lot of information regarding 5.2 and even 5.3 is lost in the mix, so not to be 'you should look at updating guy', but....should look at updating A small Power9, or Power8, heck P7 lines will run rings around a p5. In fact, I'm pushing for that now, we have a few p5's still and they are dropping like flies. Lost two raid controllers (drives ok, but sissas0 AND sissas1 on same frame went belly up.) Another had sysplanar0 errors. And a 3rd I keep under my desk in the office as a heater in the winter months has been reporting predictive failure on the service processor for at least a year now if not longer.


Sorry trevian, I may not be much help in the long run.
Feel free to post what you can, and I'll try to assist when I can, but just all before my time. Perhaps one of the mods here who've worked with AIX for a really long time may have some other ideas?