Boeing and 787 operators around the world began installing modification kits in their Dreamliners last Friday after the U.S. Federal Aviation Administration approved the manufacturer’s proposed “fix” to their battery systems. Guidance for accomplishing the modification came in the form of an FAA-approved service bulletin, issued ahead of a “superseding” Advisory Directive due for publication in the Federal Register this week. Along with the approval of the battery adaptation, the FAA finished its review of the 787’s 180-minute ETOPs (extended twin-engine operations) clearance and opted not to reduce it, meaning the Dreamliner’s effective range on transpacific flights will not change.
The new AD, written to supersede the January 16 emergency directive that broadly required unspecified modifications to the battery systems “in accordance with a method approved by the manager” of the FAA’s Seattle Aircraft Certification Office, will require 787 operators to install containment and venting systems for the main and auxiliary system batteries, and to replace the batteries and their chargers with modified components. Speaking on a conference call from Seattle Friday afternoon, Boeing 787 chief project engineer Mike Sinnett said the installations will take roughly five days to perform. Noting that each airline followed its own policies in procedures for inducting an airplane into service, however, he wouldn’t estimate when the first revenue flight might occur.
The FAA said it will closely monitor modifications of the aircraft in the U.S. fleet to ensure proper compliance with instructions. The agency added that it will stage teams of inspectors at the modification locations and not allow any airplane to return to service until after it accepts the work.
Sinnett said that Boeing has already deployed 10 AOG (aircraft on ground) teams consisting of some 300 modification specialists to locations around the world to begin installing the systems and that battery maker GS Yuasa will start shipping new powerpacks “immediately.” Meanwhile, Boeing began releasing modification kits stored at various staging locations near each operator. In a statement, Boeing said airplanes will undergo modification “approximately” in the order it delivered them.
The modifications include an adaptation of the charger and battery-monitoring unit designed to narrow the acceptable level of charge–in essence, lowering the maximum charge allowed and raising the minimum level of discharge allowed. Engineers have also devised a way to “soften” the charging cycle in a way to put less stress on the battery.
Within the battery itself, the new design uses an electrical insulator between each of the eight cells to isolate them from each other and prevent what Sinnett calls “propagation.” Electrical and thermal insulation above, below and between each cell prevents heat migration, while small holes drilled into the bottom of the case that encloses the cells and battery management unit allow moisture to drain away from the battery. Larger holes in the sides of the case allow a failed battery to vent more efficiently, thereby lessening the possibility of damage to other parts of the power pack.
Finally, the new design calls for the use of a stainless-steel enclosure meant to isolate the unit from the rest of the equipment in the electronic equipment bays and deprive any potential source of fire within the box of oxygen, thereby preventing ignition.