Boeing says no diversion is needed in its new 787 Li-ion battery design
With pictures of emergency ground crews swarming still fresh in their minds, 's engineers say they have devised a solution so foolproof that pilots will not need to interrupt a flight should a lithium-ion battery failure occur.
â€śThe worst-case battery failure doesn't even require the airplane to divert,â€ť Vice President and Chief 787 Engineer Mike Sinnett said as the company rolled out a team of more than 300 engineers to put the 50 grounded 787s back into service. Boeing has acted not by redesigning the aircraft's electrical architecture, which depends on the high power ratings of lithium-ion (Li-ion ) batteries for initial starts, but by modifying the batteries and enclosures, he says.
The company acted after the's April 19 approval of its solution to prevent thermal runaways from spreading catastrophically from cell-to-cell in either of the aircraft's two 32-volt Li-ion batteries.
All the 787s Boeing had delivered since September 2011 were grounded by the FAA, Japan Civil Aviation Bureau (JCAB) and other national emergency airworthiness directives following two incidents on aircraft operated by Japanese airlines. They acted after a fire broke out in the aft unit of a(JAL) 787 at Boston's Logan International Airport on Jan. 7, and an (ANA) 787 en route from Tokyo to Yamaguchi had to divert to Takamatsu, on the island of Shikoku, on Jan. 16 when fumes escaped from its forward battery enclosure.
The grounding left eight carriers with airplanes in an aircraft-on-ground (AOG) situation at 17 locations worldwide, meaning they could not fly until repaired. In the U.S., United had six 787s at four airports; in Japan, Boeing said ANA and JAL had 24 spread across six airports.
By April 24, Boeing's engineering teams were installing kits in 10 of the grounded aircraft and nine of the 25 undelivered 787s parked at its factories. The company was working in the sequence of deliveries, 787 Program Manager Larry Loftis said. That scenario favors ANA and JAL, which have a combined 24 aircraft,
Boeing suspended deliveries after the FAA and JCAB acted, and it does not expect to resume them until early May. But Chairman/CEO James McNerney says it can still meet its commitment to deliver more than 60 787s this year because it kept producing during the flight suspension.
The FAA has superseded its emergency airworthiness directive in the Federal Register April 26, but the JCAB has not said when it will approve flights.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 toof 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. â€śWhat we have now is a system where we account for the possibility that a cell may fail,â€ť Sinnett says. â€śAnd indeed it may.â€ť
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(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.
â€śIt's been a long haul, that's for sure,â€ť 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 â€śare not of the intended quality,â€ť Sinnett says. Generators are also being upgraded â€śto the latest standardâ€ť 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.