SkyWest forecast Wednesday that first-quarter results would be lower than it expected because of factors including a recent grounding of some aircraft, sending its shares down 13 percent.

SkyWest, whose units operate regional flights for Delta and United, said it expects net income of between USD$4.5 million and USD$7.5 million for the first quarter.

The company said its Atlantic Southeast Airlines unit had "significant" weather-related cancellations at its Atlanta hub during the first quarter. The unit also grounded 60 regional jets after an internal audit raised concerns that some engine inspections were missed.

ASA canceled about 750 flights more than normal as a result of the groundings and bad weather, SkyWest said.

Additionally, SkyWest said it expects to record a pre-tax charge of about USD$7 million in the quarter tied to a decline in value for certain security investments.

It also said expenses from reduced block-hour schedules provided by major partners would hurt first-quarter results.