Boeing's 787 could be back in service as early as next month if the FAA approves the package of battery modifications the manufacturer devised after the two failures that led to the grounding of the fleet in January.

It is a big “if,” however, and given the unexpectedly long time Boeing took to complete testing of the lithium-ion battery fix, the manufacturer is taking nothing for granted as it waits for the agency to make its move. One optimistic sign of a swift outcome is the announcement by United Airlines, the only U.S. operator of the 787 to date, of provisional plans to resume services with the aircraft on May 31.

United aims to start using the 787 for the first time on flights between Houston and Denver at least a week earlier than the previous June 5 target. It also plans to resume international operations on flights from the U.S. to Tokyo around June 10, also assuming the FAA approves the battery fix.

The airline is keeping its options open, though. “We are in the process of formulating our domestic flying plans and will be making additional schedule changes as we gain visibility into the timeline for certification and modification work,” the carrier said in a statement. All the potential start dates fall well beyond the two days of NTSB public reviews of lithium-ion battery use and the FAA's certification process for the technology in the 787. The FAA declines to comment on whether the hearings, scheduled for April 23 and 24 in Washington, will have any material impact on the timing or substance of its expected response to Boeing.

Boeing officially completed the final certification test for the modified 787 battery system during a demonstration flight for the FAA on April 5 using Line No. 86, a production aircraft destined for LOT Polish Airlines that has been used for the bulk of recent flight testing. Prior to that trial, Boeing also completed the crucial ground test of a deliberately failed battery on 787 development aircraft ZA005, clearing the penultimate test hurdle.

While the FAA and Japanese Civil Aviation Bureau (JCAB) are reviewing the test data, Boeing is preparing a service bulletin detailing the modification package. This will be issued once regulators indicate that the modification provides a means of compliance with the terms of the U.S. and Japanese airworthiness directives (AD). The FAA and JCAB will then each revise their respective ADs, the issuing of which prompted the grounding of the fleet in mid-January following two battery failures on aircraft operated by All Nippon Airways and Japan Airlines.

Working with airline teams in Japan, Qatar, Chile and the U.S. Boeing will then install the modified battery system in the aircraft. An ANA aircraft in Japan will be the first to receive it; a team of Boeing engineers has begun preparatory work there in anticipation of FAA/JCAB approval. Each modification is expected to take 4-5 days to perform, pending completion of the modification and pilot refresher training.

Boeing is also using the 787 downtime to develop, test and certify a series of other systems improvements to areas that proved troublesome during the aircraft's initial service period. The work included testing a revised power panel design, an improved engine anti-ice system and upgrades to the back-up standby instrument displays and crew information system (CIS), a Honeywell-developed aircraft health-monitoring feature that forms part of the 787's central maintenance computer.

Boeing says that, following FAA clearance to resume test flights, it has been conducting “routine test flights designed to address some of the component reliability projects we have been working. One such flight last week was to conduct testing to address some of the power panel improvements we have been working. We are always working to improve component reliability, and a new airplane program always has some start up issues. This work never stopped. In fact, during the return to flight work we're doing with the airlines, we will be addressing several improvements that should help further improve the 787's overall reliability and performance, including screening of power panels and several other activities.”

Ground tests of new software for the aircraft's power electronics cooling system (PECS) were also undertaken. The PECS dissipates the heat created by the large, high-voltage motor controllers that condition the variable-frequency power generated by the engines and auxiliary power unit (APU) for use by aircraft systems. Although portions of the large motor power system are energized by the APU battery, the changes are related to the overall electrical system upgrades rather than being associated with the battery modification.

The power panel was the source of early in-service issues with the 787, at least one of which on an ANA aircraft in April was traced to a short circuit in one of the units. Power panel malfunctions were also behind a string of events in December that triggered error messages indicating failures of the aircraft's starter-generators.