A report by the US National Transportation Safety Board has said that the three-month world-wide grounding of Boeing 787 Dreamliner aircraft in 2013 was due to a battery defect that was “poorly addressed” by both manufacturers and regulators.

Two battery fires in January of last year — one in the USA and the other in Japan — were caused by an internal short-circuit in the battery, which led to a “thermal runaway” that produced smoke and fire.

The report said that Boeing’s “management” of Thales Avionics (which designed the electrical conversion system) and GS Yuasa (which made the batteries) “did not ensure” that manufacturing was “consistent with established industry practices”.

In addition, the US aerospace giant “incorrectly” assumed that the impact of a short-circuit in the battery would be limited; the group “did not consider the most severe effects of a short-circuit, or how to mitigate such a risk”.

Furthermore, the US National Transportation Safety Board said that the US Federal Aviation Administration also “did not recognize the potential impact of an internal short-circuit and, as a result, did not require adequate testing for it”.

A Boeing spokesman said: “We remain confident in the comprehensive improvements made to the 787 battery system following this event, and in the overall performance of the battery system and the safety of the airplane.”