U.S. regulators have proposed to fine Pinnacle Airlines Corp. US$1 million for alleged maintenance violations, including a lapsed inspection for engine-related cracking.

Pinnacle, a feeder carrier for Delta Air Lines Inc., United Airlines, and US Airways Group Inc., flew two Canadair regional jets in 2009 and 2010 that were not in compliance with safety regulations, the Federal Aviation Administration said on Friday.

In one case, Pinnacle operated a jet on 40 flights without performing necessary structural inspections of an engine casing, the FAA said.

During that time, the FAA said, an existing crack grew by half-an-inch to 4 inches in length. The part would have to be replaced if the crack on the General Electric Co. engine had grown another half-inch.

Pinnacle said it inadvertently missed the inspection date and addressed it immediately once it discovered the oversight. The aircraft has returned to service.

The proposed fine also covers allegations Pinnacle flight crew members performed tasks on another aircraft over 23 flights that should have been done by maintenance workers.

This involved attaching a support cable that keeps the aircraft door from hitting the ground when opened at the gate.

Pinnacle said it is discussing the proposed civil penalty with the FAA. It is unclear whether the airline will challenge the fine, as many carriers do.