The US Federal Aviation Administration (FAA) has cleared Boeing to begin test flights soon on an instrumented 787 that could pave the way for a return to flight with an interim solution for the battery problem that has kept the fleet grounded for more than three weeks.

Boeing's flight test crew will be required to perform a pre-flight inspection and monitor the status of the batteries during take-off and cruise, the FAA says. The flight test aircraft must landed immediately if the crew receives an in-flight status message regarding the battery, the agency says.

Boeing and FAA officials are assured that flight tests can resume safely, even as US and Japanese safety investigators continue to search for an elusive root cause of a short-circuit within one of the eight battery cells.

The FAA itself is continuing to review the 787's entire electrical system in case other battery-like faults slipped through the certification process, while the agency's original decision to clear the lithium-ion battery as airworthy is itself under investigation now by the US National Transportation Safety Board.

Test flights will resume on board the flight test aircraft ZA005, the first 787 to fly with the General Electric GEnx-1B turbofan.

The fifth Dreamliner test aircraft was also used during the flight test programme for functions and reliability testing as part of the partially successful effort to gain extended operations (ETOPS) certification. The FAA cleared Boeing at entry into service for 180min ETOPS, but not the 330min level the airframer was seeking.

"We are confident that 787 is safe to operate for this flight test activity," Boeing says in a statement.

Several external battery experts have criticized the architecture of the 787 battery design as inherently unsafe, as a short-circuit and over-heating problem in one cell can easily spill over into the other densely packed battery cells. That leads to an uncontrollable chain reaction called thermal runaway.

One of the most outspoken critics of Boeing's battery design welcomed the resumption of flight tests, if it involves an improved architecture.

"The changes proposed are steps in the right direction. Are they enough? I can't say. That needs to be determined by in situ testing," says Donald Sadoway, a materials chemistry professor at the Massachusetts Institute of Technology.

Source: Air Transport Intelligence news