The FAA approval nevertheless moves airlines an important step closer to tapping the full potential of the Dreamliner, which burns 15 percent less fuel than the Boeing 767. The approval was of little concern to investors, one Wall Street analyst said. Boeing's stock was up 0.4 percent at $134.70. But the approval appeared to come sooner than expected and its timing was seen by some as a sign of continuing tension between the two agencies, one charged with investigating accidents and the other with ensuring safety. "It certainly does seem like there's some conflict between the NTSB and the FAA," said Richard Aboulafia, an analyst at the Teal Group in Fairfax, Virginia.

Richard Aboulafia, a prominent aviation consultant, said the Dreamliner will be crucial for American as it competes with United and Delta to attract premium passengers on international routes. He suggests that American will fly it to Asia, the Middle East and secondary cities in Europe. "It is absolutely the plane you want to fly point-to-point internationally," he said, "and it's at its best at longer ranges" where the fuel efficiency pays off most.