Boeing’s Battery Fix Preserves 787 Systems

By Michael Mecham
Source: Aviation Week & Space Technology

The FAA has superseded its emergency airworthiness directive in the Federal Register April 26, but the JCAB has not said when it will approve flights. The FAA estimates the cost to United Airlines of fixing each airplane and revising its maintenance program at $2,788,578. United is the only U.S. carrier flying the 787. Each installation will need a regulatory sign-off before the aircraft can return to service.

The kits take about five days to install and include a 1/8th-in.-thick stainless steel battery enclosure, vent line assembly, battery charger, wire bundles and associated hardware. The enclosure is designed to meet a 300C event without thermal risk to the aircraft. New batteries, which have been redesigned to better insulate their eight cells, are being shipped directly to carriers from the Kyoto-based manufacturer, GS Yuasa.

Besides isolating cells better to thwart thermal runaways, the improved installation is designed to rob the battery of the oxygen necessary to sustain a fire by venting fumes overboard. “What we have now is a system where we account for the possibility that a cell may fail,” Sinnett says. “And indeed it may.”

Sinnett would not comment on why a more advanced fail-safe solution was not designed from the start, referring to a technical review last week by the National Transportation Safety Board (see following article). But an immediate explanation exists in why Boeing selected Li-ion technology over more traditional nickel-cadmium batteries in the first place. Boeing favors a more-electric architecture in the 787, and Li-ion batteries held out the promise of far more power with less weight. Adding the new enclosure/venting system robs the aircraft of that weight advantage, but the 787 still benefits from the higher power rating of Li-ion batteries.

The main battery is located forward in the electric/electronic (E/E) equipment bay below the cabin floor by the front passenger doors. It powers main engine start, ground operations and provides backup power. The second battery, in the aft E/E bay, starts the auxiliary power unit and provides emergency flight instrument and cabin lighting.

The FAA lifted the prohibition against 787 test flights a day before it approved Boeing's battery fix. That flight clearance also means carriers are free to seek permission from their regulators to ferry grounded aircraft to maintenance centers. Functional test flights are not typically required once an AOG aircraft is repaired, Sinnett says, but Boeing will perform check flights of all the modified 787s.

“It's been a long haul, that's for sure,” Sinnett said of the 94 days it took Boeing to devise a solution acceptable to the FAA. That down period far exceeds the agency's last similar grounding in 1979, when DC-10's type certificate was suspended for 57 days because of pylon cracks.

Besides the battery kits, Boeing installation crews are addressing some unrelated issues, including replacing power panels that “are not of the intended quality,” Sinnett says. Generators are also being upgraded “to the latest standard” and some hydraulic tubes are being made more robust, he says.

Sinnett notes that the grounding did not prompt regulators to limit the 787's 180-min. extended operations certification rating so no additional action will be needed when airlines resume operations.

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