DALLAS – Southwest Airlines said it has grounded 44 of its Boeing jets to inspect for possible structural damage.

The airline’s decision comes as it faces regulatory and congressional investigations into its decision last year to keep flying 46 jets that required safety inspections for fuselage damage. The FAA has proposed a record $10.2 million fine for those violations.

Southwest is canceling about 4 percent of its schedule Wednesday, including some flights related to weather, said Southwest spokeswoman Linda Rutherford. That would indicate around 135 to 140 cancellations.

Rutherford said the airline has identified 44 airplanes from its Boeing 737-300 and 737-500 fleets that needed inspections of the aircraft skin above and below the windows along the fuselage

Of those, 38 are being taken out of service Wednesday for the inspections, which take about 90 minutes per airplane, she said. One of the 44 previously had been retired, and five were already undergoing other maintenance work, she said.

The carrier hopes to complete all the inspections in time to operate a full schedule Thursday, she indicated.

“At this point, we’re not canceling flights for tomorrow,” she said on Wednesday.

The inspections are related to Southwest’s internal investigation of its maintenance operations and its compliance with required work.

“During part of the audit process last night, we asked Boeing for a clarification on a Boeing service bulletin that’s related to aging aircraft skin,” she said. Southwest had already decided “out of an abundance of caution” to ground the airplanes to do the checks, she said, before Boeing indicated that the checks were needed.

Carl Kuwitzky, president of the Southwest Airlines Pilots’ Association called it a “minor inconvenience” and said the jets would likely be back in service sometime Wednesday.

“They are trying to clear it up and do what the right thing is,” Kuwitzky said. “They are taking a conservative approach, even if that looks bad.”

Southwest informed the FAA about the decision to ground the jets earlier Wednesday morning, FAA spokeswoman Laura Brown said.

As of Dec. 31, 2007, Southwest flew 520 Boeing 737 jets, including 194 of the older Boeing 737-300 that have been the target of the stepped-up fuselage inspections.

Southwest said Tuesday that it had placed three employees on leave in connection with an internal investigation into the safety lapses.