The US Federal Aviation Administration (FAA) has approved Boeing's proposal to fix battery issues on the 787 Dreamliner, allowing the airframer to conduct limited test flights on two aircraft even as a safety investigation continues.

Boeing would be required to conduct "extensive testing and analysis to demonstrate compliance" with safety regulations, says the FAA today, almost two months after it grounded the 787 fleet on 16 January.

"This comprehensive series of tests will show us whether the proposed battery improvements will work as designed," says US Transportation Secretary Ray LaHood. "We won't allow the plane to return to service unless we're satisfied that the new design ensures the safety of the aircraft and its passengers."

Boeing's proposal involves three layers of protection to prevent overheating in the lithium-ion batteries that power the 787's auxiliary power unit: improved separation between the battery cells, installing ceramic-plated spacers between each of the cells and the addition of a containment and venting system so smoke cannot enter the passenger cabin.

"We are confident the plan we approved today includes all the right elements to conduct a comprehensive evaluation of the battery system redesign," says FAA administrator Michael Huerta. "Today's announcement starts a testing process which will demonstrate whether the proposed fix will work as designed."

The FAA says Boeing's proposal would require the airframer to pass a series of tests before the 787 is returned to service.

"The plan establishes specific pass/fail criteria, defines the parameters that should be measured, prescribes the test methodology and specifies the test setup and design," says the FAA. The agency's engineers will be present during testing and will be involved in the process, it adds.

The agency has approved limited flight tests for two aircraft, which will have the prototype versions of the new containment system installed. "The purpose of the flight tests will be to validate the aircraft instrumentation for the battery and battery enclosure testing in addition to product improvements for other systems," says the FAA.

Boeing says the flight tests will be conducted on two aircraft: line number 86, which will be used in tests to demonstrate that the proposed solution works in flight and on the ground; and test aircraft ZA005, which will conduct engine improvement tests unrelated to the battery issue.

The airframer says additional testing may be scheduled as needed, and will provide additional details of the improved battery design in the days ahead.

Boeing Commercial Airplanes president and chief executive Ray Conner says the airframer has a "great deal of confidence" in its solution.

"Working with internal and external experts in battery technology, we have proposed a comprehensive set of solutions designed to significantly minimise the potential for battery failure while ensuring that no battery event affects the continued safe operation of the airplane," he says.

Boeing says the test plans for its proposed solution were written based on the FAA's standards as well as guidelines published by the advisory committee, Radio Technical Commission on Aeronautics. These guidelines were not available when the original 787 battery certification plan was developed, says Boeing.

Boeing had submitted the proposal to the FAA on 22 February. The FAA grounded the 787 fleet on 16 January after two incidents in which the batteries overheated on two 787s, resulting in a fire in one case. The agency's move led to a global grounding of all in-service 787s worldwide.

Source: Air Transport Intelligence news