Three major airlines were among 11 US carriers that failed during an unprecedented industry review to demonstrate full compliance with government safety directives, regulators said on Friday.

The Federal Aviation Administration did not disclose the carriers or their shortcomings, flagged during the second part of a two-phase review of industry safety practices that ended in June. No major airlines were tagged for lapses in the first phase, which was conducted in March.

The second and more detailed audit involved closer scrutiny of records, procedures and aircraft. All questions regarding specific aircraft were addressed before they were allowed to fly again, authorities said.

FAA officials touted the overall safety of the US airline industry, which carries more than 600 million passengers a year. The agency reported a 98 percent compliance rate with its directives, prompting acting FAA administrator Robert Sturgell to bristle at questions regarding the small fraction of cases where carriers fell short.

"This audit gives us confidence that, overall, the system is safe and in almost every instance the airlines are complying with our safety directives," Sturgell told reporters. "Even with this tremendous level of safety and compliance, we still have work to do."

The FAA has been under pressure from Congress to tighten oversight of airlines after a whistleblower case earlier this year uncovered inspection and oversight lapses at Southwest Airlines, which was fined a record USD$10.2 million. Southwest has resisted FAA demands for payment.

Sturgell and senior aides would not discuss individual cases under investigation but indicated the problems were not as serious as the Southwest matter, which involved flying planes that were overdue for inspections covering fuselage cracks.

Nor are the shortcomings on par with lapses at American Airlines, Delta Air Lines and other carriers, which grounded hundreds of planes and canceled thousands of flights last spring for incomplete wiring work.

Officials repeatedly mentioned record-keeping problems but said no airline, aircraft type or safety directive stood out as singularly problematic. There is no evidence at this point that airlines willfully disregarded directives, officials said.

The FAA examined more than 5,600 directives in the review. These advisories, most made in collaboration with the aircraft of systems manufacturer, typically range from matters as simple as floor lighting to complex and costly or engine inspections and related work.

Nevertheless, the agency continues to investigate those that fell short and did not exclude the possibility of fines or other penalties. There is no timeline for completing the investigations.

Sturgell said all compliance issues raised during the FAA review were resolved before specific aircraft were allowed to fly.