A similar situation happened to me once when I used some UA MP miles for an intra-South America trip flying GRU - EZE rountrip. The C-class award roundtrip was 30K miles vs a Y-class roundtrip requiring 20K miles. I went for c-class on Varig roundtrip.

Upon checking in for first Varig segment (GRU-EZE), gate agent tells me that plane has been downgraded from C/Y config to an all coach config and hands me my boarding pass. Given that loads were heavy that day, there were no other C-class seats available at all to take and I ended up flying coach. I decided I'd write a letter and request 5K miles reimbursement since I didn't get award I paid mileage for. The letter back from UA MP told me that I would not get reimbursement since they "had no control over the aircraft downgrade" and a "sorry you were inconvenienced" message. I was annoyed but didn't do anything else about it. Perhaps I should have fought for more?

At GRU, I didn't even think to ask for any kind of compensation since I didn't know this was a possibility. Do any of you think I would have gotten anything? Please keep in mind this was on Varig back in 2006.....

putonog