What happened
On September 23, 2017, a Boeing 777-200, registered PH-BQC, operated by KLM Royal Dutch Airlines, departed Kansai International Airport for Amsterdam. During the initial climb and acceleration phase over Osaka City, a right aft wing-to-body fairing panel (Panel 198AR) detached from the aircraft. The falling component descended into Kita-ku, Osaka, where it struck a moving vehicle, causing a dented roof and a broken rear window. There were no injuries to the occupants of the vehicle or the 321 people on board the aircraft.
Upon receiving notification of the ground impact, the flight crew performed inspections of the cabin pressurization, flight controls, and fuel systems. After consulting with the airline's maintenance control center and the aircraft manufacturer, the captain determined that the aircraft's structural integrity remained intact and continued the flight to Amsterdam.
The investigation
The Japan Transport Safety Board (JTSB) examined the detached panel, the attachment hardware, and the aircraft's maintenance history. Investigators analyzed the condition of the screws and bolts used to secure the fairing, as well as the structural integrity of the underlying brackets. The investigation also reviewed the manufacturer's service bulletins and the airline's part management procedures.
Physical examination of the panel revealed that several mounting screws had broken and that the bolt holes had become significantly enlarged. While investigators identified the use of five improper bolts—which had a different diameter and grip length than the required specification—they determined this was not the primary cause of the separation. The focus shifted to the condition of the mounting bracket, which was an older-design version manufactured via a bending process rather than precision machining.
Findings
- The primary cause of the panel's departure was the fatigue fracture of the pre-enhancement bracket used to secure the forward upper corner of the fairing.
- The use of the older-design bracket, which had lower dimensional accuracy and strength, allowed for a gap to form between the panel and the fuselage.
- This gap permitted airflow to enter behind the panel, creating aerodynamic pressure and vibration that eventually led to the bracket's failure and the panel's detachment.
- The use of improper bolts was noted but considered a negligible factor in this specific incident, as no air leakage was observed in the areas secured by those specific bolts.
Safety action
Following the incident, the aircraft manufacturer issued a service bulletin (SB 777-53-0088) instructing operators of older-model 777 aircraft to replace the pre-enhancement brackets with more robust, enhanced-design brackets. The operator involved in the incident completed the replacement of similar brackets across its fleet by December 2017 and implemented improved fastener management to prevent the accidental use of incorrect hardware.