A Transportation Department investigation has concluded that Federal Aviation Administration officials covered up safety errors at Dallas-Fort Worth International Airport, the second such admonishment in the past three years.

A spokeswoman for the department's inspector general said a report of the investigation's findings should be released Friday. She confirmed the general findings as outlined in documents released late Thursday by the U.S. Office of Special Counsel.

The report was requested by the special counsel's office, which is tasked with protecting government whistle-blowers. That office said in a statement that between November 2005 and July 2007 FAA managers intentionally misclassified 62 instances in which airplanes were allowed to fly closer together than they were supposed to, attributing the errors to pilots or categorizing them as nonevents in an attempt to shift blame away from air traffic controllers at the Texas airport.

The inspector general previously had confirmed a similar underreporting of safety errors at the airport in 2004. After that incident, FAA officials promised to take steps to fix the problem.

After Special Counsel Scott Bloch, who recently resigned, requested a second investigation this spring by the inspector general, FAA officials acknowledged that the misclassifying of safety errors had continued and that the agency was taking steps to correct the problem.

The inspector general's report confirming a second series of deliberate misclassifications had not previously been released.

Acting Special Counsel William Reukauf, in a letter Thursday to President George W. Bush, said increased "scrutiny of FAA and its implementation of the corrective measures proposed to resolve the continued misconduct and mismanagement is critical."

According the special counsel, the inspector general's report recommends 10 corrective measures be taken in response to the coverup, including a reorganization of air traffic control management at Dallas-Fort Worth and a top-to-bottom review of FAA's overall air traffic safety management.

FAA spokeswoman Laura Brown said the agency has already implemented all of the inspector general's recommendations that don't relate to personnel matters, which she is prohibited from discussing.

"I can tell you we take them very seriously, and we're taking appropriate action on those as well," Brown said.

The National Air Traffic Controllers Association has said previously that safety errors by controllers have increased nationally because airport towers and other traffic control facilities are understaffed and experienced controllers are leaving the FAA. Controllers and the FAA are at an impasse in contract negotiations.

The continued problem at the Dallas-Fort Worth airport became public only because a whistle-blower — controller supervisor Anne Whiteman, who first reported in 2004 that agency officials were concealing safety violations — came forward again last year to say the FAA managers were still underreporting safety violations by controllers or misreporting them as pilot errors.