Boeing plans to modify the lithium-ion batteries in the 787 Dreamliner and subject them to more rigorous testing before installing them in heavy-duty steel boxes that vent outside the aircraft, measures it says eliminates the risk of battery fires and provides safeguards against future incidents like those seen aboard two Dreamliners in January.
Although investigators have not determined the root cause of a problem that has grounded all 50 Dreamliners worldwide since January, Boeing said it can assure federal authorities, airlines and the public that its flagship aircraft is safe, and there is no chance of a battery fire. The steps it outlined during a press conference in Japan on Friday will, it said, ensure any future incidents involving a battery failure will not affect other systems.
“Everyone feels very comfortable with what we are doing,” said Ray Conner, Boeing’s CEO of commercial aircraft. “I plan to fly on the very first flight.”
Boeing says it has been working nonstop on the solution, which the Federal Aviation Administration has approved, since joining the National Transportation Safety Board in investigating a Jan. 7 battery fire aboard a 787 at the gate in Boston. A week later, a second Dreamliner making a domestic flight in Japan made an emergency landing after the crew received messages in the cockpit indicating a battery had overheated and failed. The two incidents prompted the Federal Aviation Administration to ground all Boeing 787 aircraft registered in the United States. Aviation agencies worldwide quickly followed suit in what was the first grounding of an American-built airliner in more than 30 years.
Boeing says it has been testing the new battery system with the FAA for more than a week and expects to complete certification within weeks. Most of the testing will occur on the ground, with a single test flight planned to demonstrate the new system in flight. Mike Sinnett, the company’s chief project engineer on the 787, said the the new design “eliminates the possibility of fire,” in the battery system.
To minimize the chance of a single cell failure spreading, Boeing plans to more thoroughly protect the eight individual cells within the 63-pound battery. The battery itself will be installed inside a stainless steel box with walls one-eighth of an inch thick. Contrary to what has been said in recent weeks, Sinnett told reporters the box is not simply designed to contain a fire, it prevents one from starting.
Boeing unveiled a mockup of the stainless steel battery box that will house the lithium-ion battery in the 787 Dreamliner. Photo: Boeing
“This enclosure keeps us from ever having a fire to begin with,” he said, referring to the newly designed container. He said there is not a sufficient amount of oxygen to “contribute to combustion” should the battery overheat or experience a short circuit. During six weeks of testing, he said. engineers used external heaters to intentionally overheat the battery in an attempt to induce a short. When the cells subsequently vented hot electrolyte as designed, engineers tried without success to ignite the vented gasses. Even after pumping additional oxygen into the box failed to ignite the mixture for more than an instant.
“There was a small amount of combustion for 200 milliseconds and it went out again,” Sinnett said.
Boeing’s previous battery tests during original certification included crushing cells, driving nails through them and intentionally introducing short circuits to induce failure. Boeing found “nothing adverse happened” during these tests, and so it expected the battery’s box and existing internal protection to be sufficient. The company says it followed the certification process set out by the FAA.
A diagram of the new steel box with the titanium vent tube to the exterior of the airplane. Image: Boeing
Sinnett made a point of noting that investigations on the United States and Japan found no evidence of a fire inside the battery. Observations of the battery aboard the plane in Boston indicated small, three inch flames near an external connector, he said. And during the inflight failure in Japan, there was no fire, and the system alerted the pilots as designed and the electronics bay containing the battery automatically reconfigured to vent the overheated battery away from the cabin or cockpit.
The new design provides even greater safeguards. Should a cell rupture within the redesigned steel box, the gases would open a pressure release disc, a valve of sorts, which would vent the electrolyte mixture through a one-inch titanium tube to the exterior of the aircraft. Each of the two batteries has its own vent tube, and the system is designed to eliminate the chance of gasses or smoke emanating from a failed battery entering the aircraft. Boeing says the vents will require placing two small holes in the fuselage, but they will not affect the structure of the aircraft. The FAA requires that the holes do not result in the vented gases reentering the aircraft downstream.
Beyond bolstering the box, Boeing is improving battery testing at the manufacturing level. In a separate conference call, Ron Hinderberger, Boeing’s vice president of 787 engineering, told reporters each of the eight cells within each battery will be tested repeatedly under heavy loads of 18 kilowatts. Individual cells will be held to tighter parameters regarding changes in voltage and temperature. Boeing plans to perform the new tests on all new batteries, as well as those already in service. Any cell that doesn’t fall within the new standards will not be used.
Boeing is also replacing the shielding material in between each cell, which was rated for 150 degrees Centigrade, with phenolic glass rated at 500 C to isolate and protect the cells.
“We made changes to avoid propagation from one cell to another, better heat resistant sealing and added high temperature dielectric isolators above and below the battery cell,” Sinnett said. “We also added dielectric protection in the spaces between them.”
In addition to revising the battery, Boeing will modify the charging system to narrow the range of acceptable charge. In a bit of dispute with the NTSB, which has called the incidents in Boston and Japan “thermal runaway,” Sinnett said Boeing’s definition of thermal runaway can only occur due to overcharging — something he said has not happened aboard a 787.
“We are confident that we have never seen overcharging in the fleet,” he said.
From Boeing’s perspective, thermal runaway occurs when extensive heat and an uncontrolled fire “basically consumes the entire battery,” Hinderberger said. What happened aboard the planes in Boston and Japan was, he said, “thermal propagation.”
Semantics aside, Boeing said the new design minimizes the likelihood of a battery failure of the type seen in Boston and Japan. And the company made a point of noting the battery system worked as designed in both cases, with no significant damage to either airplane.
Both Sinnett and Hinderberger were careful not to imply a battery will not fail on a 787 in the future, but said the new design insures such a failure will not threaten the safety of the flight.
“We know at the airplane level, there will be no significant impact,” Sinnett said.
One catch to the new design is that it adds 150 pounds to the weight of the airplane. This weight gain eliminates one of the big selling points for lithium-ion batteries to begin with. Boeing says the other advantages including the lack of a memory-effect for lithium-ion and the better shelf life still justify its use.
The company said it has completed about one-third of the FAA certification testing for the new design. Beyond lab testing, two airplanes will be used to demonstrate to the FAA that the design is safe. But in a bit of a surprise, the company says only a single test flight will be performed with a 787 heading to Poland’s LOT airlines. The company’s test aircraft, ZA005 will be used to perform tests on the ground.
Boeing implied that it expects the new design to be approved in a matter of weeks, but much of the detail outlined Friday pertains specifically to FAA testing. Officials in Japan are conducting their own investigation, and the safety director with Japan’s aviation regulating body told Reuters it was “inappropriate” for Boeing to discuss when flights may resume.
For its part, Boeing says the FAA certification testing is about 75 percent complete, but there was no mention of when the Dreamliner will fly again.
