Despite experts' best efforts to get to the bottom of the mishaps involving Boeing Co.'s 787 Dreamliners, pinpointing the causes may take a while, leaving the timetable for their return to the skies uncertain.

All Nippon Airways Co., which has more 787s than any other airline, said Thursday it expects a ¥1.4 billion revenue drop in January. It had to cancel around 460 flights after regulators grounded all Dreamliners worldwide following the emergency landing of a 787 on Jan. 16 due to a battery problem that caused smoke in the cockpit.

Nine days earlier, a battery on Japan Airlines Co. 787 caught fire on the ground in Boston.