Hong Kong (CNN) -- The woes of Boeing's new 787 mount as U.S. regulators ordered airlines to stop flying their Boeing 787s.
The U.S. move comes after two fleets of Boeing 787s have been grounded in Japan after alarms and a burning smell in the cabin forced a Dreamliner to make an emergency landing Wednesday.
The incident is the most serious in a spate of problems that have bedeviled the new aircraft, and comes after the U.S. Federal Aviation Administration, which is responsible for air safety, launched a comprehensive examination on Friday of the Dreamliner's design as well as its manufacture and assembly.
"The Boeing 787 incidents have taken on a new seriousness with the grounding" by All Nippon Airways (ANA) and Japan Airlines (JAL), said Richard Quest, CNN's aviation correspondent.
"The potential of fire on board an aircraft is among the most serious issues in aviation," he said. "The plane is still safe to fly. However, Boeing must ensure the reliability of the aircraft for the airlines and the confidence of the traveling public to fly on the planes.
"That is the fundamental problem that Boeing is now facing," Quest said.
As CNNMoney reports, a Boeing 787 operated by All Nippon Airways was forced to make an emergency landing Wednesday in Japan. The domestic aircraft was traveling to Tokyo when irregular battery activity and smoke in the forward electrical compartment were detected. The aircraft then made an emergency landing at Takamatsu airport after a burning smell was detected in the plane's cabin.
Following the incident, both All Nippon and Japan Airlines said they were immediately grounding their Dreamliner fleets -- which effectively grounds about half of the Dreamliners now in operation worldwide. The Japanese airlines were among the first to take delivery of the Boeing 787. ANA has 17 aircraft, while JAL has seven Dreamliners.
Worldwide, Boeing has delivered 50 Dreamliners -- but hundreds more are on order. More than 150 Dreamliner flights occur daily, according to Boeing.
What problems has the Dreamliner had?
In recent weeks, many. The most recent Dreamliner setbacks occurred Friday. Oil was discovered leaking from a generator on an engine at a Japanese airport, and a crack appeared in a cockpit window of a plane en route from Tokyo to western Japan, a spokeswoman for All Nippon Airways said.
On January 8, a Japan Airlines flight bound for Tokyo aborted takeoff from Boston's Logan International Airport after a pilot on another airplane spotted the 787 leaking fuel. On January 7, a maintenance worker discovered the electrical fire aboard an empty plane being prepared at a gate at Logan for a return trip to Japan. Another Japanese flight was cancelled last week after sensors detected problems with the plane's braking system.
In December, a United Airlines 787 traveling from Houston to Newark, New Jersey, was diverted to New Orleans because of mechanical problems. A general inspection of all 787s in September turned up cracked engines on two planes.
The woes come after the debut of the plane in 2011 -- nearly three years behind its production schedule.
Do Dreamliners fly in the U.S.?
United Airlines -- which has six 787s -- debuted the nation's first domestic Dreamliner routes last November. "We continue to have complete confidence in the 787 and the ability of Boeing," United said Friday in a statement. The airline described the problems as "early operational issues."
United's Dreamliner fleet travels primarily on routes connecting Houston and Chicago and between Newark and Los Angeles. Last week, the airline kicked off its first international 787 service between Los Angeles and Tokyo. Other U.S. carriers are in line to buy Dreamliners, including Delta. American Airlines has announced an order, but it's not yet "firm."
What does the troubles mean for Boeing?
The company's stock has taken a hit as the troubles mount. Several hundred are under order, making its success crucial for Boeing, which had not designed a new commercial jetliner in years before unveiling the Dreamliner.
"The 787, being a new airplane, does have teething problems," John Goglia, a former member of the National Transportation Safety Board, told CNN last week. It's common for new planes to have "these kinds of problems," he added.
Airlines have been excited by the Boeing 787 as the first mid-size, long-range airplane, which would allow airlines to open up routes where they don't have enough demand from passengers to justify a larger plane like a Boeing 747 or an Airbus A380.
Boeing has more than 800 unfilled orders from airlines around the globe that will take years to fill. In addition to the Dreamliner assembly line at its Seattle-area factory, it built a new 1,000-worker factory in South Carolina to handle the demand. It hopes to double production of the plane this year to about 10 a month.
CNNMoney's Charles Riley and CNN's Yoko Wakatsuki and CNN Wires staff contributed to this report