WASHINGTON – Federal aviation officials said Friday they are investigating 17 cases in which 11 air carriers did not comply with government safety directives.

The cases were uncovered during a major effort by the Federal Aviation Administration to verify whether air carriers follow the agency's safety orders as required.

The first phase of the inquiry earlier this spring found seven instances in which four carriers had not complied with safety orders. FAA officials declined to identify the carriers and said they did not know if some of the new cases involve carriers already under investigation.

The inquiries were announced by FAA administrator Robert Sturgell, who said 98 percent of the 5,600 safety directives audited by the agency had been followed by the carriers. He said the relatively few cases in which safety directives weren't followed indicates there is a high level of safety in the U.S. air traffic system. He noted that the U.S. hasn't experienced a major airline accident in over two years.

“These kinds of numbers are not an accident, it's not a miracle, it's not luck,” Sturgell said. “It's the result of an entire team effort – the government, the industry, Congress, everybody involved in the aviation system – producing the safety net we have today.”

David Castelveter, a spokesman for the Air Transport Association, which represents the airline industry, said the association is pleased with the audit findings.

Besides the 17 cases, most of the discrepancies uncovered by the audits “were generally technical and did not impact safety,” Castelveter said. Nevertheless, they “serve as a useful reminder that we can always do better,” he said.

The FAA has been under fire from members of Congress who say it has treated the airlines it oversees as clients, fostering a cozy relationship at odds with vigilant safety enforcement.

Agency inspectors testified at a congressional hearing in April that their jobs were threatened when they reported maintenance and inspection problems with some airlines.

FAA took the rare step this spring of ordering the audit of maintenance records at all domestic airlines following reports of missed safety inspections at Southwest Airlines. The Dallas-based airline was hit with a record $10.2 million fine for continuing to fly dozens of Boeing 737s, which carried an estimated 145,000 passengers, that hadn't been inspected for cracks in their fuselages.

Last month, FAA announced it's seeking $7.1 million from American Airlines for flying airliners after safety problems were reported and for drug-testing violations.

In June, the Department of Transportation launched an investigation into FAA practices, including how the agency reviews flight risk, its air carrier compliance measures and its oversight of maintenance practices.