As federal transportation safety officials continue investigating the flaws in a Boeing Co. jetliner’s battery systems that led investigators to ground the 787 Dreamliner fleet, there is growing scrutiny of the Federal Aviation Administration’s practice of letting manufacturers self-certify the safety of critical aircraft systems.

“This is an issue when you have a regulator with limited resources,” National Transportation Safety Board Chairwoman Deborah A.P. Hersman said last month, raising concerns about the budget-driven practice.

The issue is likely to be a focus of congressional oversight in light of the grounding of the 787s. Senate Commerce, Science and Transportation Chairman Jay Rockefeller, D-W.Va., has already said his panel will look into the aircraft’s problems, although he has not yet scheduled hearings.

The FAA began a big push toward self- certification in 2005, when it created the Organizational Designation Authorization program. Expanding the reporting roles of safety managers employed by manufacturers would “allow the FAA to concentrate its resources on the most safety-critical matters,” the agency said in a Federal Register notice published that October.

Certification work by the FAA had “increased five-fold over the last 50 years,” the notice read, creating a labor crunch. Ultimately, a need to cut costs drove the change.

“We determined that the rule will generate both improved safety and reduced costs,” officials wrote. “We will be able to more efficiently use our resources while extending our oversight coverage, thereby increasing safety.”

Chicago-based Boeing, the nation’s largest exporter, was an early adopter of the FAA’s expansion of self-certification. In 2009, the company was allowed to deploy 400 of its own inspectors to complete reports on behalf of the FAA. A team of 30 FAA employees oversee the operation, auditing the inspectors and reviewing their reports. While the vast majority of the oversight work is conducted by the Boeing inspectors, FAA employees must issue final approval of aircraft safety.

Hersman said the safety board will continue probing whether that revised safety-system certification played a role in missing problems with lithium-ion batteries in the 787s.

Federal authorities grounded the aircraft type after overheating batteries caused smoke onboard planes in Japan and at Boston’s Logan International Airport. Getting the 50 aircraft the company has already delivered back into the air is critical for Boeing, which already has taken more than 800 orders for the aircraft, which carries a price tag of about $200 million each.

But the process of identifying the problem and fixing it is unlikely to be over soon. All Nippon Airways, a Japanese carrier with the most 787s, has canceled flights on the aircraft through May.

Investigators have already determined that “a short circuit in the battery caused failures,” Hersman said at a news conference last month updating reporters on the status of the investigation. NTSB officials are still looking for the cause of the short circuits, which likely include “battery charging, the design and construction of the battery, and the possibility of defects introduced during the manufacturing process,” she said.

“Our task now is to see if enough — and appropriate — layers of defense and adequate checks were built into the design, certification and manufacturing of this battery,” Hersman said.

The ultramodern jet marked a departure from traditional manufacturing processes. It was designed using ultra-light composite materials instead of traditional metal, promising improved energy efficiency and enhanced passenger comfort.

It also ushered in big changes at Boeing, bringing in many new suppliers that were overseen under the FAA’s revised self-certification model. In the case of the 787, the FAA issued more than three dozen “special conditions,” or regulations for “a novel or unusual design feature.”

That included the lithium-ion batteries that have caused problems with the 787s. The FAA noted that the batteries have “certain failure, operational, and maintenance characteristics” that differ from types used in existing aircraft. In certifying the batteries as being ready to fly, Boeing said it expected an overheating incident that caused smoke to happen once in 10 million flight hours for the fleet. The rash of incidents that grounded the 787 happened with fewer than 100,000 flight hours logged.

Hersman questioned whether the self- certification model at the FAA is working.

“You can delegate some of the action, but you can’t delegate responsibility,” said Hersman, whose agency makes safety recommendations that generally carry weight with lawmakers, though the safety board does not set policy itself.

For its part, Boeing is continuing to work with NTSB and FAA officials to identify a fix for the 787’s battery and get the aircraft back into regular service. The company says it is also willing to revisit and strengthen oversight.

“We are working corroboratively to address questions about our testing and compliance with certification standards, and we will not hesitate to make changes that lead to improved testing processes and products,” Boeing said in a statement.

If the NTSB does determine that flaws in the certification process played some role in the fleet’s battery problems, aides for lawmakers in both parties say the policy would be a likely target for changes in future legislation.

It’s unlikely, though, that any changes to the current inspection system would come quickly. Congress just enacted a four-year reauthorization (PL 112-95) for the FAA a year ago. It ordered the agency to further streamline its certification processes beginning this month “in a manner than supports and enables the development of new products and technologies and the global competitiveness of the United States aviation industry.”