New Delhi, July 30 -- Three of America's four largest airlines reached the same conclusion in the span of two months: humanoid robots are a battery-safety problem, not a passenger amenity. Delta Air Lines moved first in June. Southwest Airlines had quietly barred them in May. On July 23, United Airlines became the third major carrier to prohibit humanoid and quadruped robots in both the cabin and checked luggage. JetBlue and American Airlines have not yet followed, leaving an inconsistent national policy at a moment when the category of device being banned is just beginning to appear in the commercial market.

the technical term for a lithium battery failure that can produce fire. Aviation safety regulators have spent years building rules...