Careful here. The regulation is that overpayments can be recovered over a six month period, BUT not at a rate less than the period it was overpaid. An LTA advance is usually given all at once; therefore, the recovery of an overpayment is normally all at once. However, I'm curious as to how an over-advance of LTA could put a member in dire straits. Unless he/she drew the advance, didn't take the trip and then spent the money (in which case the sympathy factor is very low), there is no way he/she should have been given that much money in the first place.
Having said all that, the member can still bring it up to the CoC and something can probably be done. Making personnel destitute is counterproductive.
Now to relate an amusing story (at least to me - not to the member it happened to). Years ago, there was a young sailor who was not the sharpest knife in the drawer who owed money to just about everybody in the dockyard. Around Christmas time he decided to go home on LTA. This was a guy who grew up in Nfld and all his documentation said he was a Newfoundlander. However, come time for him to draw his LTA advance, his mother had suddenly moved to Edmonton. Apparently, his parents had spit up and his mother had gone to Edmonton to live with his brother. After explaining the rules, I gave him the advance he needed to get to Edmonton.
After Christmas, I asked him for his receipts and stamped leave pass. He'd forgotten them at home. The next day, I asked again. Apparently his roommate had cleaned up his apartment and he couldn't find them. The next day the Chief Clerk called his mother - in Newfoundland! She had never moved to Edmonton and in fact was still married and living with the sailor's father. He had never been to Edmonton. I immediately recovered the money from his pay (had to cancel some allotments to do it as well). Money wasn't a big problem for him after that. He got his trip to Edmonton- all expenses paid, with an escort and shiny new bracelets. ;D