The Federal Aviation Administration has operated that way for many years, even as government audits have found those efforts were sometimes poorly overseen and led to errors. The agency in 2005 began allowing Boeing and other manufacturers to pick the engineers, who previously were chosen by the FAA.
"I think everyone recognizes there is an inherent conflict there," Jim Hall, former chairman of the U.S. National Transportation Safety Board, said in an interview.
The FAA and NTSB are reviewing the Dreamliner's certification process, including tests used to approve Boeing's use of lithium-ion batteries, after two incidents nine days apart involving the power packs forced the worldwide grounding of the 787 two weeks ago. It was the first grounding of an entire plane model by the U.S. in 34 years.
The FAA doesn't have the budget to hire enough engineers to do all testing and certification itself, Hall said. Also, the agency in some cases doesn't have the necessary expertise to assess the latest designs, a former FAA manager and aviation engineers said in interviews.
"It allows the FAA workforce to focus on the most critical systems and the new technology," said John McGraw, a former FAA deputy safety director who now operates a consulting firm in Stafford, Virginia.
"It's hard for the public to accept the concept for someone else to make a finding for the government," he said. "But this has been done since the start of the FAA. This is really just an extension of that, with better oversight than they had back then."
The agency can overturn decisions by outside engineers and must sign off on all decisions, according to an e-mailed statement it provided. Engineers in the program must agree to act on behalf of the government.
"We provide rigorous oversight," the agency said. "If the FAA sees any evidence that a delegation system is compromised, the agency will revoke the authority."
Most countries follow the FAA's lead in regulatory matters, though they do their own certifications of new planes and can order additional tests or data.
The FAA's statement didn't address how the Dreamliner's lithium batteries were approved in 2007, four years before the plane entered commercial service, and the NTSB hasn't released any information on that process from its investigation. The 787 was the first all-new Boeing model since the 777 debuted in 1995.
Clues to how the FAA certified the batteries can be found in the steps it took to be sure that the 787's carbon-fiber structure was as strong and durable as the aluminum-based aircraft that preceded it.
Boeing employees known as designated engineering representatives oversaw tests to demonstrate the design's strength, according to a U.S. Government Accountability Office report in 2011.
FAA's engineering staff was responsible for overseeing the "more significant tests and documents" and took steps beyond what was required to oversee the new design, the GAO said.
An 11-page directory of companies allowed by the FAA to choose engineers to certify designs and components lists Boeing and other companies that worked on the 787 program. Those include Thales SA (HO), based in Neuilly-Sur-Seine, France. Thales makes the Dreamliner's power packs that include batteries made by GS Yuasa Corp. (6674), based in Kyoto.
Engineers designated by the FAA, including Boeing employees, have done an equivalent job to what the agency's own engineers would have done, Bret Jensen, a spokesman for the Chicago-based company, said in an interview.
"The 787 was certified following the most rigorous test program in Boeing's history and the most robust certification program ever conducted by the FAA," Jensen said.
"We are confident in the regulatory process that has been applied to the 787 since its design inception."
The U.S. Transportation Department's inspector general, in a 2011 review of all FAA's aircraft certifications, found 45 instances in which non-agency engineers hadn't complied with the rules. The inspector general didn't name the companies involved.
One unidentified manufacturer couldn't show it had conducted "critical tests" on a new engine component, the inspector general found. Another manufacturer didn't follow rules for emergency oxygen supplies for passengers and crew, according to the report.
The FAA agreed to make changes, including keeping a database of approved outside engineers to ensure that anyone with a history of performance issues would be barred from the program, according to the report.
Neither the GAO nor inspector general cited evidence that the program has led to a safety lapse on a Boeing plane.
The Transportation Safety Board of Canada pointed to engineering certification as a possible factor in the crash of Swissair Flight 111 off Nova Scotia on Sept. 2, 1998, that killed all 229 aboard.
Engineers at an aircraft maintenance company who were acting on the FAA's behalf signed off on an entertainment system that may have started a fire that brought down the plane, the Canadian safety board found. The engineers lacked sufficient knowledge of the Boeing MD-11's power grid to provide that certification, the board found.
The FAA in response reviewed the entertainment system's approval and found it was done correctly, according to an inspector general report in 2004.
Hall, who led the NTSB from 1994 through 2000, said the safety board investigated several accidents in which the certification of an airliner was questioned.
He stopped short of calling for the FAA to stop using outside engineers, while saying he would recommend a public hearing on the battery certification if he was still chairman.
The system has adequate checks and balances to ensure safety, Larry Timmons, president of Aircraft Engineering Specialists Inc. in Bellevue, Washington, said in an interview. Timmons has been approved by the FAA to certify aircraft wing designs since 1969.
From 1998 to 2004, the FAA removed 770 designated engineers for poor performance, according to the 2004 GAO report. Some FAA employees felt that the agency should have acted in more cases, according to the report.
The 2011 inspector general's report didn't say how many removals have occurred since the program was changed, though it refers to one engineer whose authority was rescinded.
The threat of the FAA discovering an error keeps the vast majority of outside engineers honest, Timmons said.
"You build this reputation up," he said. "It's relatively easy to destroy. You don't get many chances to make a mistake."
Alan Levin in Washington: firstname.lastname@example.org