JetBlue Airways Corp. JBLU, -0.26% reported Thursday June load factor that slipped to 86.9% from 87.0%, as an increase in seat supply outpaced growth in demand. The air carrier said capacity rose 4.8% to 5.30 billion available seat miles, while traffic grew 4.7% to 4.61 billion revenue passenger miles. The company said it expects second-quarter revenue per available seat mile (RASM) to increase 3.1% from a year ago, which is within its guidance range of 2.0% to 4.0%. The stock, which was still inactive in premarket trading, has rallied 17.9% year to date, while the NYSE Arca Airline Index XAL, +0.39% has advanced 16.2% and the S&P 500 SPX, +0.45% has hiked up 19.4%.