Shares of United Airlines Holdings Inc. UAL, +0.62% jumped 4.7% in premarket trading Tuesday, after the air carrier raised its passenger revenue outlook, citing an improving demand environment. United disclosed late Monday in a filing with the Securities and Exchange Commission that it now expects second-quarter total revenue per available seat mile (TRASM) to be up 23% to 25% from the same period in pre-pandemic 2019, compared with previous guidance of a rise of about 17%.