Two days after the FAA cleared Boeing to fly 787 test missions over unpopulated areas, the company took prototype ZA005 on an “uneventful” flight over Washington state on Saturday. During the two-hour, 19-minute flight, 13 Boeing pilots and flight-test personnel used special equipment to observe and record details of the performance of the main and APU batteries during normal flight conditions. Boeing wouldn’t comment on what data it gathered, citing its potential bearing on the investigations into the battery failures that occurred last month on Japan Air Lines and All Nippon Airways airplanes.
If nothing else, the event marked perhaps the most visible sign of progress in Boeing’s three-week-long effort to return the 787 to service, as costs associated with the grounding of the worldwide fleet and resulting delay of new deliveries continued to mount. Last week Boeing alerted Norwegian Airlines of possible delays to deliveries scheduled for late April and June, adding another airline to the list of customers liable to seek compensation for lost revenues.
Norwegian, which had signed a lease deal for its first two airplanes with Los Angeles-based ILFC, issued a statement last Thursday outlining plans to enter a separate three-month lease deal for another long-range aircraft in the event it doesn’t receive its first 787 in time for planned services from Oslo to New York and Bangkok on May 30 and June 1, respectively.
References to threatened delivery dates as far into the future as late April seemed to support suggestions that the airplanes could stay grounded for months following reservations expressed by the chairman of the U.S. National Transportation Safety Board over the legitimacy of several assumptions underlying nine special conditions applied in the certification of the 787’s lithium-ion battery system.
During the NTSB’s latest briefing on its investigation into the January 7 fire aboard a Japan Air Lines 787 at Boston Logan Airport, board chairman Deborah Hersman reported that the airplane’s flight data recorder showed that the total voltage in the failed APU battery unexpectedly dropped from a full charge of 32 volts to 28 volts, suggesting failure of a single four-volt cell. Further evidence uncovered during the examination of the battery suggests that “thermal runaway” began with internal short circuits in one of the power pack’s eight cells and spread to adjacent cells, causing the fire.
However, in the course of testing during the certification process to meet the special conditions, Boeing found no evidence of what Hersman termed cell-to-cell propagation or fire. Boeing also determined that a single-cell failure would result in smoke emission less than once in every 10 million flight hours. Hersman reported that the 787 fleet had accumulated less than 100,000 flight hours before the second failure.
“This investigation demonstrated that a short circuit in a single cell can propagate to adjacent cells and result in smoke and fire,” said Hersman. “The assumptions used to certify the battery must be reconsidered.”
Next the NTSB plans to examine the safety certification process used by the FAA and Boeing for the battery design “and determine why the hazards identified in [the] investigation were not mitigated,” added Hersman. The safety board expects to open the public docket for comments and produce an interim factual report by February 6.