Federal officials are seeking $655,125 in fines against Alaska Airlines and its Horizon Air affiliate for alleged safety violations, including failing to inspect a plane for cracks.

The Federal Aviation Administration said Thursday that Horizon operated a Bombardier Dash-8-400 aircraft on 45 flights, while it failed to follow a safety order to check for cracked or corroded fittings on the engine housing.

A 2011 order required airlines to inspect the fittings every 300 hours of flight time and make repairs as needed. The FAA said Horizon used the plane on at least 45 passenger flights in March 2011 after it had passed the 300-hour mark.

The FAA proposed a civil penalty of $445,125 against Horizon.

The FAA also said it would seek a $210,000 civil penalty against Alaska Airlines, charging that the airline failed to properly tag turned-off equipment before making repairs to Boeing 737 jets. It said the violations of worker-safety rules occurred 10 times in 2010 and 2011.

Both airlines are owned by Seattle-based Alaska Air Group Inc.

Company spokeswoman Bobbie Egan said Horizon performed the required inspection of the fitting over the engine covering, "however, we did not properly document our maintenance due to a misunderstanding over wording on the work order." She said the plane was pulled from service the next day after the documentation mistake was spotted, was inspected again and passed.

Egan added that Horizon is replacing the fittings with ones that don't require such frequent inspections.

On the Alaska planes, she said, the maintenance work was done to Boeing's specifications but not properly documented. She said passengers were never in danger.

The airlines have 30 days to respond to the FAA.

Alaska Air Group shares rose 21 cents to close at $33.23.