787 battery certification test plan to be conducted under stricter regulatory guidelines
and 787 operators around the world may be breathing easier following U.S. approval of the manufacturer's battery system redesign certification plan, but the hard work is only just beginning,
As the grounding of the 787 stretches into an unprecedented 10th week, Boeing has been told by the FAA the aircraft will only be cleared to return to service after the manufacturer conducts “extensive testing and analysis to demonstrate compliance with the applicable safety regulations and special conditions.”
The question now for operators and Boeing is how much “extensive testing” will be required, particularly since this time around the process will also involve testing to a far more stringent level than when the 787 was first certificated. In addition to the standard FAA Part 25 certification requirements, the augmented test plan for the improved battery system for the first time includes guidelines published by the RTCA, formerly known as the Radio Technical Commission on Aeronautics. RTCA is a regulatory advisory committee which most recently has been guiding ruling on advanced navigation practices.
Boeing says the RTCA guidelines were simply not available in the 2000s when the original 787 battery certification plan was developed. Although much of the relevant RTCA committee battery and electrical system expertise resides within Boeing itself, the FAA appears satisfied with the overall certification plan, which will involve a series of tests that show how the improved battery system will perform in normal and abnormal conditions.
Among the tougher tests to be conducted will be an evaluation of the containment system's ability to withstand a deliberately induced thermal runaway. This self-propagating phenomenon was cited by the(NTSB) in its March 7 interim report on the first battery failure on a 787 in early January. Although not identifying a specific cause, the report described several shortcomings in both the baseline battery system design and the original means of testing and certification of the device.
The NTSB has announced plans to hold a forum and investigative hearing in April to review the battery's technology, safety and process used in its certification. The agency's investigation found—among other things—no record of the final production-standard charging system having been tested with the actual GS Yuasa-made battery. According to the NTSB report, Securiplane, the charging system developer, tested the unit with a simulated electric load instead of an actual battery. The company apparently took this precaution after having earlier suffered a fire at its facility during battery testing.
News of the approval on March 12 was greeted with huge relief by Boeing, which proposed its redesign package to the FAA on Feb. 22. Since the original issues forced the grounding of the worldwide fleet on Jan. 16, the company has been focused on an urgent redesign effort.President Ray Conner and 787 Vice President and chief project engineer Mike Sinnett unveiled the first official details of the battery system improvements at a press conference in Tokyo on March 14. The chief changes included a revision of the internal battery components to minimize the chances of initiating a short circuit, as well as better insulation of the cells and the addition of a new containment and venting system (see graphic, p. 28).
“This comprehensive series of tests will show us whether the proposed battery improvements will work as designed,” says U.S. 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.” FAA Administrator Michael Huerta adds the agency is “confident the plan . . . includes all the right elements to conduct a comprehensive evaluation of the battery system redesign.”
The plan lays out a series of pass-fail criteria, and “defines the parameters that should be measured, prescribes the test methodology and specifies the test setup and design. FAA engineers will be present for the testing and will be closely involved in all aspects of the process,” the FAA adds.
Flight tests of the prototype revised battery containment system will be conducted using Line No. 86, an aircraft designated for. Aviation Week was the first to report this same aircraft being previously used for ground tests of the battery system in mid-February (AW&ST Feb. 18, p. 32). The modified battery has also been installed in test aircraft ZA005, though Boeing says this is to allow testing to resume of the planned performance improvement package (PIP) II engine upgrade. The FAA says flight tests will validate instrumentation for the battery and testing its enclosure in addition to improvements for other systems.
Explaining the triple-layered safety improvements in the revised battery system, Boeing's Conner says the design will prevent faults from occurring and “isolate any that do.” It also incorporates enhanced production, operating and testing processes. “In the unlikely event of a battery failure, we've introduced a new enclosure system that will keep any level of battery overheating from affecting the airplane or being noticed by passengers,” he adds.
Boeing says the enhanced production and testing processes include “more stringent screening of battery cells prior to battery assembly.” Operational improvements also focus on tightening of the battery system's voltage range. This addresses another finding of the NTSB interim report that the battery did not behave as either Boeing or the system subcontractorindicated. In particular, the battery's power discharge was “not at the constant rate described by the Boeing or Thales documents and included large changes and reversals of power within short periods of time,” it notes.
Operators and lessors express encouragement at the FAA's approval of Boeing's fix. Speaking at the Istat Americas 2013 conference in Florida, Air Lease Corp. Chairman and Chief Executive Steven Udvar-Hazy said the move is “. . . positive. Customers are looking forward to getting it back in the air and certainly this is a good step forward. I'm happy the FAA is taking a constructive role with Boeing in moving this forward.”