As new Boeing 787s continue to stack up at Everett and others remain idle around the world, the airframer’s battery crisis is finally coming to a head as the FAA decides on whether to approve a company plan to return the aircraft to the skies.

If the FAA says yes, airline sources tell Aviation Week that the first 787s could begin operating again with an interim battery system modification as early as the third week of March. If it says no to the near-term proposal, then Boeing faces the far more painful and expensive alternative of developing and certifying a longer-term fix while the fleet remains grounded.

There are no easy decisions facing FAA Administrator Michael Huerta, who is scheduled to hear Boeing’s proposal from a delegation led by Commercial Airplanes President Ray Conner on Feb. 22. This marks the 38th day since the agency grounded the 787, one more day than the McDonnell Douglas DC-10 grounding in 1979.

The FAA response, which is not expected until Feb. 25 at the earliest, and perhaps not for several days beyond that, also requires approval from Ray LaHood, the U.S. transportation secretary. LaHood earlier raised the bar on conditions for a 787 reprieve by saying the aircraft will not return to service until authorities are “1,000% sure” it is safe.

Adding to the pressure on the FAA is the ongoing review of its original certification of the 787, as well as the yet-to-be-completed National Transportation Safety Board investigation into the first lithium-ion battery failure on a Japan Airlines aircraft Jan. 7 at Boston Logan International Airport. The NTSB, and its Japanese counterpart, the Japan Transport Safety Board (JTSB), are still evaluating the root cause of multiple battery failures that prompted a world-wide grounding of the 787 on Jan. 16.

As part of the investigation, engineers are looking at what could have caused a mechanical flaw inside the battery in service. While even the NTSB has stated that it has found no signs of overcharging, one part of the research still focuses on how a faulty charging process could lead to damage and subsequent overheating and smoke, ultimately causing the destructive sequence known as a thermal runaway. If confirmed, that would be a significant finding because it would redirect attention to the charging system, rather than the battery.

However both investigations so far have failed to pinpoint an exact cause, and with Boeing and its customers facing growing costs over the grounding, there are signs the FAA may be increasingly open to a compromise to get the jet back into service. The multi-point Boeing plan is thought to cover a phased approach toward a fully modified lithium-ion battery system. The short-term fix focuses on a new containment system for the existing unit, together with added venting ducts for smoke and additional monitors. It also is thought to incorporate additional crew procedures to check battery health and status via the engine indication and crew alerting system before, during and after flight.

Boeing is not discussing details of its proposal, but the supplementary venting understood to form part of the plan is expected to be routed to a dedicated overboard vent valve already built into the aircraft’s equipment cooling and ventilation system.

The short-term fix package, if approved, would be flight-tested immediately to satisfy the anticipated FAA requirements, as well as to pave the way for a fast-paced retrofit program. Boeing is already reporting “good progress” on tests of the revised configuration, which up until now has been evaluated only in its systems integration and component laboratories in Seattle.

Conner’s proposal package is also believed to include longer term options for a revised configuration that would minimize the chances of a battery overheating in the first place, as well as from being destroyed in a thermal runaway. These would include a more significant redesign of the battery itself with the provision of interstitial space and possibly insulation between individual cells, additional voltage and temperature monitors and cooling. The longer-term fix likely would be undertaken through a supplemental type certificate, say regulatory agency sources.

Boeing, which revealed additional details of the aircraft’s battery and related electrical system features on Feb. 20, says only that it is “working tirelessly in cooperation with our customers and the appropriate regulatory and investigative authorities. Everyone is working to get to the answer as quickly as possible, and good progress is being made.”

Boeing’s move comes as investigators from the JTSB reveal that two cells in the second battery of the All Nippon Airways (ANA) 787 that made an emergency landing at Takamatsu Airport on Jan. 16 were ”swollen” Although the emergency was prompted by problems with the main battery, which was badly damaged by burning electrolyte, the signs of apparent degradation were found in the auxiliary power unit (APU) battery located in the aft electrical/electronic equipment bay.

The APU battery in the ANA incident was initially thought to be undamaged, but JTSB says subsequent tomography scans have revealed evidence of slight swelling in the cells. The agency also reported signs of miswiring around the battery, although the significance of this has not yet been explained.

If the FAA pushes Boeing toward the longer-term solution only, the manufacturer almost certainly will face new questions over its 787 production and storage plans. While Boeing is adamant it will not slow down production and has told its suppliers not to expect any changes, not all of them are convinced. The CEO of one major 787 supplier says his company already has run separate calculations on several slowdown and subsequent ramp-up scenarios. He doubts that Boeing can sustain its current strategy beyond a period of months and would be forced to react more forcefully if it turns out the grounding will be extended beyond the summer.

Saying it is “incredibly hard” to judge what is actually going to happen, the executive notes that at some point his company is likely to make its own decision on 787 parts production, even if Boeing has not changed its stance by that time. Jefferies & Company analyst Howard Rubel believes that “pushing the solution to May is probably as far as the program can be stretched.”

Boeing’s position to stick to lithium-ion-batteries has been dealt a further blow by Airbus’s decision to drop the technology for now. Airbus reverts back to nickel-cadmium-batteries for the A350 program, although the initial flight tests will still be performed with the lithium-ion devices on board as it is too late to change the design before first flight, which is anticipated for May or early June.

Airbus says the decision is not safety-related. But the manufacturer is concerned that possible additional regulatory requirements to be imposed by the European Aviation Safety Agency (EASA) could put the current program schedule at risk, which will see first delivery of the aircraft in the second half of 2014. According to industry sources, Airbus has also dropped the idea of using lithium-ion for the A320NEO family.

Even though the battery design on the A350 differs materially from Boeing’s design on the 787, different suppliers are used and the A350 has fewer electrical systems than the Boeing aircraft, Airbus made design changes to the battery system one year ago. The modification addressed safety concerns, Airbus CEO Fabrice Bregier said earlier this month, and Airbus claims it is still confident in the technology. It plans to work further to mature it and could look at retrofitting the lighter and more powerful batteries even on the A350 at a later stage once the current uncertainties are sorted out.

Airlines, meanwhile, continue to make contingency plans to cover for the continued grounding of the 787. United Airlines expects to see the aircraft remain out of service through March 30, while Air India expresses hope that the 787 will be back in operation by early April.