There has been articles telling that Boeing 787 planes are grounded over safety concerns in USA. The Federal Aviation Administration has ordered U.S. airlines to stop operating the Boeing 787, after a series of battery and fuel system failures have called into question the airworthiness of the newly developed composite aircraft. Japan’s two biggest airlines grounded all their Boeing 787 aircraft for safety checks Wednesday after one was forced to make an emergency landing in the latest blow for the new jet. Here is my collection on what I have found written on the recent Boeing 787 problems.
The 787, known as the Dreamliner, is Boeing’s newest and most technologically advanced jet, and the company is counting heavily on its success. Since its launch 787 plane has been plagued by a series of problems including a battery fire and fuel leaks. There are always teething problems with any new aircraft and airlines often are reluctant to be the launch customer of any new airplanes. You need to ensure safety, and then you also have to get people to feel that the jet is 100 percent safe. The problem here for one of America’s largest manufacturers is enormous. Developing a whole new model of airplane is expensive.
Over the years the demand for electrical power has increased in planes as new technologies such as fly-by-wire (FBW), digital avionics, and in-flight entertainment (IFE) systems are introduced. This is in addition to other power demand increases, such as the on-going change from hydraulic and pneumatic systems to electrically powered systems. Dreamliner 787 uses lots of electrical power for actuators and more, compared to earlier aircraft. Why? That’s easy to answer: in order to reduce weight and get the benefits of electronics and advanced algorithms, much of the conventional hydraulic power and control of the aircraft has been replaced by electrically-based power and control, and with advanced electronics and software, of course. Plus, the airframe is also largely made of up composites for reduced weight, instead of conventional aluminum.
Taking a Peek into Boeing 787 Electrical Power System article tells 787 will generate five times the electrical power than its predecessor (767)! 787 electrical system is 230V system (most other aircraft systems operate at 115V AC or 28V DC). The electrical power generation on board a 787 is 1.4 megawatt. The environmental control system (ECS), anti-ice system and hydraulic system are all electrically driven (making it more efficient than traditional bleed air extraction and air turbines). The electrical system is more critical to the operation of the Dreamliner than on previous Boeing aircrafts. The new electrical system has it’s benefits, but also problems. Boeing Investigates 787 Dreamliners for Electrical Issues. The More Electric Aircraft – Why Aerospace Needs Power Electronics slide set has some slides that give you some details on 787 electrical system. In 787 generator provides variable frequency supply that is directly connected to power bus. Nearly all aircraft loads will require power converters.
These electrical systems require lots of batteries for start-up, backup, and even operation. The preferred rechargeable energy-storage technology for the batteries is based on lithium-based chemistry. This makes sense, since lithium offers much, much higher energy density (by weight and volume) than any other available battery chemistry. Boeing 787 and Lithium Ion battery failure article tells that the 787 is the first airliner to make extensive use of lithium-ion batteries to help power its energy-hungry electrical systems. The batteries charge faster and can be better molded to space-saving shapes compared with other airplane batteries.
So what are the reasons behind the latest problems in 787. Lithium-Ion Batteries Emerge as Possible Culprit in Dreamliner Incidents. All Nippon Airways has ground its fleet of 17 Boeing 787s after an aircraft made an emergency landing following a suspected battery problem. ANA said a cockpit message showed battery problems and a burning smell was detected in the cockpit and the cabin. An inspection of the All Nippon Airways 787 that made an emergency landing in western Japan found that electrolytes, a flammable battery fluid, had leaked from the plane’s main lithium-ion battery. Investigators found burn marks around the damage. Keep in mind what appears to be “the problem” often is just a misleading manifestation of the real problem elsewhere.
The fluid is extremely corrosive, which means it can quickly damage electrical wiring and components. The electrolyte fluid conducts electricity, so as it spreads it can short circuits, interfere with electrical signals and make control of the plane impossible for pilots and ignite fires. Aviation experts said the energetic quality of lithium-ion can be a concern onboard aircraft. “One of the issues with lithium batteries is they get very hot,” Freiwald said. “When they ignite, they can burn so hot that Halon 1301 won’t extinguish a fire.”
We do not yet know what the official cause of the Boeing 787 Lithium-Ion battery breakdown was on the two aircraft until the full investigation has been completed. Proper Lithium-Ion battery charging and safety article have some good advice from experts in the industry that show how critical a good protection scheme is in a critical design such as on a commercial aircraft. Every lithium ion battery pack should have a safety board or IC which monitors the charge and discharge of the pack, and prevents improper conditions. Lithium-ion operates safely within the designated operating voltages; however, the battery becomes unstable if inadvertently charged to a higher than specified voltage. Li-Ion batteries commonly require a constant current, constant voltage (CCCV) type of charging algorithm. The main challenge in charging a Li-Ion battery is to realize the battery’s full capacity without overcharging it, which could result in catastrophic failure. The target charging voltage of a Lithium-Ion cell is 4.2V +/- 0.05V per cell, and the protection circuits should prevent charging above the specified safe voltage. There is very little room for error if you want to use all the capacity, especially when you are charging many cells in series (you need special battery management). Consistent overcharging can cause the plating of metallic Lithium within the cell, which will cause instability, especially if the cell is of lower manufactured quality, and especially if any moisture has been introduced inadvertently during the production stage.
Lithium-ion is not the only battery that is a safety hazard if overcharged. Lead- and nickel-based batteries are also known to melt down and cause fire if improperly handled. Automakers, many of whom use lithium-ion chemistries in hybrids and electric cars, typically operate their batteries with cooling systems. Even with cooling, however, lithium-ion automotive batteries have been known to have problems on rare occasions. Lithium-ion battery energy density is so high that there’s a lot of stored energy in that small volume, and a failure such as an internal short can result in huge current flows and subsequent fires or even explosions.
So we have the typical engineering situation of a tricky tradeoff. We want the benefits of lower weight, greater efficiency, higher energy density, and so on, but we also have to accommodate and anticipate all the implications of the technology that makes it possible. While lithium chemistry has such high density and subsequent danger, just remember that hydrocarbons such as gasoline have far greater energy density than the best batteries, yet we have managed to make that explosive technology into a safe energy-storage medium and power source.
The 787 Dreamliner Scenario: How Data Can Solve Epic Messes article tells that sensors linked to analytics and diagnostic software could help companies like Boeing solve crises more quickly. Following reports of battery failures onboard Boeing’s 787 Dreamliner, the Federal Aviation Administration (FAA) has issued an “emergency airworthiness directive” temporarily grounding the airliners. And at the moment, Boeing has a big data job on its hands: figure out the root of the battery issue—and how that issue might affect the 787’s other critical systems. The incidents did motivate aviation authorities around the world to order stoppage of Boeing 787 flights, however. The FAA also announced it will work with Boeing engineers to conduct a comprehensive review of the 787’s design and manufacture, with an emphasis on the aircraft’s electrical power and distribution systems.