* FAA cites manufacturing flaws at Boeing plants
* Boeing says order makes mandatory checks it already urged
* United is alone among U.S. airlines now flying 787s
WASHINGTON, Dec 5 (Reuters) - The U.S. Federal Aviation Administration confirmed Wednesday it is requiring inspection of Boeing Co's new 787 Dreamliners after the discovery of fuel leaks traced to a manufacturing flaw at Boeing plants.
A safety order mandated inspection of fuel line couplings in the engine pylons to make sure the couplings are correctly assembled and installed, the FAA said.
The order "makes mandatory inspections already recommended by Boeing," the company said on Tuesday.
Separately, a brand new United Airlines 787 Dreamliner with 184 people aboard was forced to make an emergency landing in New Orleans on Tuesday after experiencing a mechanical problem on a flight from Houston, Texas, to Newark, New Jersey.
The mechanical issues constituted a twin blow to Boeing, which was dogged by production problems that delayed delivery of the 787 for 3-1/2 years.
United, the only U.S. operator, flies three 787s. Another 33 are in service with foreign operators, the FAA said in an emailed statement.
The fuel leaks were due to the improper assembly of the couplings at the Boeing factories, it said.
The 787-8 has one rigid coupling and one flexible coupling per engine for a total of four couplings per airplane.
The safety order, known as an airworthiness directive, requires operators to inspect for correctly installed lockwires on the engine fuel line couplings within seven days of its publication.
Within 21 days, operators must inspect the couplings to verify they have been assembled correctly.
Boeing said on Tuesday that improperly installed fuel line connectors could lead to fuel leaks, loss of engine power or fire. But it said there were "multiple layers of systems to ensure none of those things happen."
Boeing advised airlines flying the 787 to make inspections last month, and it said about half of the 33 jets in service have already been inspected.
The biggest 787 customer so far is Japan's All Nippon Airways Co, which was the launch customer and has 16 of the jets.
Boeing shares edged lower by 0.1 percent to $73.98.