Washington ? Midlevel Federal Aviation Administration officials allowed Southwest Airlines to continue flying potentially unsafe airplanes and suppressed efforts by subordinates to correct the problem, a congressional panel was told Thursday.

“If this were a grand jury proceeding, I think it would result in an indictment,” Rep. James Oberstar, D-Minn., the chairman of the House Transportation and Infrastructure Committee, said midway through testimony by nearly 20 witnesses.

Southwest Airlines’ executive chairman, Herb Kelleher, and chief executive officer Gary C. Kelly defended the safety record of the Dallas-based carrier, which faces a record $10.2 million penalty from the FAA for flying planes that should have been inspected for fuselage cracks.

Kelleher told the committee that the airline “screwed up” by continuing to fly planes that should have been grounded. But he said the FAA’s regional office gave the go-ahead for the flights while Southwest sought to fix what he described as tiny cracks that airline officials had reported to the agency.

“We should not have (continued the flights), and we have learned our lesson,” Kelleher said. “I apologize to this committee. I realize these planes should not have flown.”

Kelleher also said he wanted to counter any impression that Southwest is “just rumbling around the skies” with cracks on uninspected planes, saying the company’s aircraft are “inspected over and over and over again.”

But several FAA employees, including two inspectors testifying as government whistleblowers, presented a picture of lax enforcement, sloppy documentation and collaboration between Southwest and the FAA Certificate Management Office. Located near Dallas-Fort Worth Airport, the office is responsible for overseeing the airline’s compliance with FAA safety regulations.

“I am here today because I am concerned for the safety of the flying public,” said FAA inspector Bobby Boutris, who, along with fellow whistleblower Douglas Peters, exposed the allegations that led to Thursday’s hearing. Boutris later told reporters that he’s received a death threat. He declined to provide further details.

Other FAA employees supported their account that principal maintenance inspector Douglas Gawad-zinski and other supervisory officials were friends with Southwest personnel and were unresponsive in looking into possible safety problems involving the airline.