Taiwan's China Airlines has ruled out a maintenance error leading to an explosion involving its Boeing 737-800 plane at Okinawa's Naha airport August last year, a report released Friday by a Japanese government investigation panel showed.

The Taiwan airline has told the transport ministry's Aircraft and Railway Accidents Investigation Commission that it followed Boeing maintenance directions, according to the report.

The accident was caused by a loose bolt, which came off the inside of the plane's right wing, piercing the fuel tank, and the leaked fuel caught fire leading to the explosion, the report said.

Nobody was injured in the accident as the 157 passengers and eight crew members aboard were evacuated safely before the explosion after the fire broke out.

The commission suspects it is highly possible that the airline did not attach a washer to the bolt during maintenance work conducted about a month before the accident.

The panel plans to question the airline and Boeing further before compiling a final report, the commission said.

According to the report, the bolt falling from a column support of the right wing's lifting device pierced the fuel tank by about 4 centimeters.

China Airlines conducted a maintenance procedure of taking out the bolt once and reattaching it July 6 last year, and it is likely the washer was there before the maintenance since that particular component was checked multiple times since the plane was introduced in 2002, according to the report.

The diameter of the nut of Boeing 737-800s in the part in question was smaller than that of the hole of the column support and the bolt would fall from the column support without a washer.

Boeing has already altered the design of the part, making the nut larger, and plans to replace the old components with new ones in old models.