When a China Airlines 737NG caught fire soon after landing at Okinawa’s Naha Airport on August 20, initial suspicions centered on maintenance issues, but new developments show the problem might be more widespread than first considered. Investigators discovered that a loose bolt in the leading-edge slat track assembly–believed to have been missing a washer–pierced the wing fuel tank, allowing fuel to escape.

An FAA Emergency Airworthiness Directive issued on August 28 ordered operators of 737-600, -700, -800 and -900 versions, including Boeing Business Jets, to conduct inspections of the assembly for loose, missing or damaged parts. Air Nippon Airways inspectors report finding a missing washer in the assembly on one of their 737-700s delivered in January, which could possibly have caused a repeat of the China Airlines 737 fire. ANA officials say the airplane was so new and had accumulated so few flying hours that the leading-edge slats had not yet required examination as part of the standard maintenance procedures.