The stock's precipitous decline from nearly $45 to less than $16 from November to April has two primary factors. First, the price of oil has continued its ascent and, coupled with a lack of pricing elasticity, has become the carrier's achilles heel. The second factor is the lack of an apparent merger strategy, which was priced out of UAUA after Continental Airlines walked away.
In reality, it's very likely that oil will begin a year-long decline in coming months as the US dollar strengthens. Furthermore, UAUA will likely strike a deal with US Airways which does not currently appear to be priced in. Both factors will cause rapid increases in this highly volatile stock.