Boeing CEO James McNerney says the company remains confident in its choice of lithium-ion technology for the 787 battery, and adds that there are no thoughts of slowing down the production line despite the grounding of the aircraft.

Speaking in bullish tones on a fourth-quarter earnings call, McNerney says, “Nothing we’ve learned yet has told us that we have made the wrong choice on the battery technology. We feel good about the battery technology and it’s fit for the airplane.” McNerney’s comments come as investigators continue to probe the cause of the two battery failures that struck the 787 within days of each other earlier this month, prompting a worldwide grounding of the operational and test fleet in mid-January.

Despite intensive evaluations by Boeing, the electric system suppliers, the FAA and U.S. and Japan transportation safety boards, no firm answers have emerged on what triggered either the battery fire on a Japan Airlines 787 Jan. 7 at Boston Logan International Airport or a second failure on an All Nippon Airways aircraft that made an emergency landing in western Japan the following week. “Even though we are making good progress, we don’t have a root cause yet,” says McNerney, adding that returning the aircraft to service is the company’s “priority No. 1” for the year.

The lack of a potential smoking gun also means that it is “hard to speculate on anyone’s role,” says McNerney, downplaying reports that in the months running up to the January battery failures, numerous batteries had been replaced throughout the 787 fleet. However, Boeing’s CEO acknowledges that the rate of the replacements, which were done for maintenance, rather than safety, concerns, was “slightly higher than the rate we predicted.”

In a statement issued just before the earnings call, Boeing said batteries are “a replaceable unit on airplanes, regardless of the technology used. Everyday there are on the order of five or six batteries on Boeing airplanes that are removed and replaced—about 2,000 per year.” Specifically referring to the 787 battery,the airframer adds, “We have not seen 787 battery replacements occurring as a result of safety concerns. The batteries are being returned because our robust protection scheme ensures that no battery that has been deeply discharged or improperly disconnected can be used. The third-highest category for battery returns is exceeding the battery shelf life—this is a fact of life in dealing with batteries; they sometimes expire and must be returned.”

McNerney declined comment on how, or in what form, the FAA might allow the 787 to resume operations. “I don’t want to prejudge what form of entry into service will specifically acceptable to the FAA,” he says. Speaking on the potential impact of the extended grounding on both the program and the profitability of the company as a whole, he adds, “I can’t predict an outcome and I’m not going to.”

With no answers on root cause in hand, Boeing is maintaining a “business as usual” stance on other aspects of the 787 program, such as production and product development. The assembly rate continues toward a target of 10 per month by year-end, and production of the initial 787-9 continues, as does marketing of the -10X double stretch, whose launch still is anticipated “later this year,”McNerney adds.