JetBlue Airways (JBLU - Get Report) on Thursday said its June load factor -- a key metric used in the airline industry to measure passenger-carrying capacity -- increased to 86.9%, up from 86% in May though a slight dip from a year ago.

The Long Island City, New York-based carrier said June traffic increased 4.7% to 4.61 million revenue passenger miles from a year ago, while capacity increased 4.8% to 5.3 billion available seat miles.

Revenue passengers slipped 0.3% to 3.67 million, while departures declined 1.7% to 30,815. On-time performance, or domestic flights arriving with 14 minutes of schedule, was 70.1%, down from 77.6% in May.

JetBlue said it expects second-quarter revenue per available seat mile to increase approximately 3.1% on a year-over-year basis, consistent with its revised guidance range of 2% to 4%.

The metrics come as U.S. airlines begin releasing their quarterly earnings figures, starting with Delta Air Lines (DAL - Get Report) , which on Thursday posted stronger-than-expected second-quarter earnings and also lifted its full-year profit guidance. 

Analysts polled by FactSet are expecting JetBlue to report quarterly earnings of 55 cents a share on revenue of $2.1 billion. 

Shares of JetBlue were down 1.06% at $18.74 in early trading on Thursday. JetBlue stock got a boost last week after Credit Suisse upgraded the airline's shares to neutral from underperform.