Amid mounting signs that Boeing will have to wait longer than it hoped for FAA approval to start test flights of its proposed 787 battery fix, the NTSB has announced plans to hold a forum and investigative hearing in April to review battery technology, safety and the design and certification of the aircraft’s battery system.

News of the April events emerged as the board released a densely packed interim report on its ongoing investigation of the Jan. 7 Japan Airlines 787 battery fire at Boston Logan International Airport. This incident and a subsequent inflight battery issue on an All Nippon Airways aircraft led the FAA to ground the worldwide 787 fleet.

The report does not give a specific cause for the battery failure but details the events of the Boston incident and findings from the examination of the battery. It also cites test results of related components, initial reports on the flight recorder data and a description of the 787 electrical power system certification plan.

A list of ongoing and planned investigative activities also is included.

The report’s findings describe the shortcomings of the power system, which was designed to vent smoke overboard from the aircraft. According to the NTSB, the system failed to function because on the ground, with the aircraft’s auxiliary power unit shut down, it lacked power after the battery caught fire. “As a result, smoke generated by the APU battery could not be redirected effectively outside the cabin and aft [electrical equipment] bay.”

The finding is not surprising since the system is designed to rely primarily on differential pressure in the cabin above the bays, which draws air through the flight deck panels and the forward electrical equipment racks to create a reverse flow of air across the battery. This flow then exits through an override valve to an overboard venturi.

Boeing says that while the override mode supplies adequate cooling during cruise, it acknowledges that the airflow naturally decreases as the cabin pressure differential reduces.

The NTSB report also notes the battery did not behave as either Boeing or system subcontractor Thales indicated. In particular, the battery’s power discharge was “not at the constant rate described by the Boeing or Thales documents and included large changes and reversals of power within short periods of time,” the NTSB says.

The report also includes new details of Boeing’s initial development testing and certification assumptions for the battery. It notes, for example, that pre-production testing of the aircraft’s lithium-ion batteries did not produce a fire after an intentional short-circuit. This led Boeing to conclude that the risks of an event similar to either of the incidents that took place in January were remote.

Announcing the plans for the hearing and forum in April, NTSB Chairman Deborah Hersman says, “With the grounding of the 787 fleet, concurrent international incident investigations, redesign and recertification activities taking place simultaneously, it is essential to provide the aviation community, policy makers and the public with the factual information we are developing.” The board says the forum, which will be held in mid-April, “. . . will explore lithium-ion battery technology and transportation safety. The investigative hearing, to be held later in April, will focus on the design and certification of the 787 battery system.”

“The information developed through the upcoming forum and the hearing will help the NTSB and the entire transportation community better understand the risks and benefits associated with lithium batteries, and illuminate how manufacturers and regulators evaluate the safety of new technology,” adds Hersman.

Boeing, meanwhile, continues round-the-clock ground tests of the revised battery system design, which is housed in a strengthened containment structure. The system is set for installation in test aircraft ZA005 which Boeing says is set to begin flights as soon as it receives FAA approval.

Industry sources tell Aviation Week that the FAA go-ahead to begin flight tests now is not expected until next week. When Boeing originally proposed its redesign to the FAA and the U.S. Department of Transportation on Feb. 22, it was hopeful that FAA Administrator Michael Huerta would grant the authority to proceed by March 6 or earlier. However, the process appears to have been slowed by Transportation Secretary Ray LaHood, who this week told the Wall Street Journal that he wanted “a thorough review” of the Boeing plan. “I am going to ask a lot of questions” before a final decision is made, he added.