CHARLOTTE, N.C. ( TheStreet) -- AMR ( AAMRQ.PK) CEO Tom Horton once asked, "What's in the water in Phoenix?" when he discussed US Airways ( LCC) aspirations to merge with his airline. Whatever it is, investors seem to be imbibing large quantities. US Airways shares rose 159% in 2012, starting the year at $5.20 and ending up at $13.50. That easily beat the Amex Airline Index ( XAL), which rose 36%, besting the S&P 500's gain of 13.4%. In 2013, US Airways shares are rising again. In mid-afternoon trading Friday, shares were up nearly 6% to $14.45. Since Wednesday morning, when trading for the year began, the shares have gained 5%. Gains are being fed by expectations that a merger with AMR will be announced shortly, although the broadly held expectations regarding a Jan. 9 announcement have dissipated, due to a wide variety of unresolved matters including labor issues -- especially pilot issues. Both the U.S. Airline Pilots Association, representing US Airways pilots, and the Allied Pilots Association, representing American pilots, have yet to reach memorandums of understanding with the airline managements. USAPA officials were huddled in Charlotte Friday, discussing their MOU for the third consecutive day. Unconfimed mid-afternoon reports from pilots indicate that pilot leaders have unanimously approved sending the MOU out to US Airways pilots for a vote. Gains in US Airways Friday were also being fed by the carrier's December traffic report, which showed a 4% gain in passenger revenue per available mile. Following the release, Dahlman Rose analyst Helane Becker reiterated a buy rating, based on the carrier's cost guidance, strong PRASM growth and her expectation that a merger could come soon. She has a $21 price target for the shares. Additionally, JP Morgan analyst Jamie Baker raised his fourth-quarter earnings estimate to 22 cents from 18 cents a share; consensus is 9 cents. Baker said US Airways' seasonal decline in revenue from the third to the fourth quarter would be about 7.6%, less than the typical decline of between 8.2% and 8.6%, which is "further evidence that demand trends appear largely intact." Follow @tedreednc-- Written by Ted Reed in Charlotte, N.C.