Incident Description
While parked at the gate to unload passengers, a pressurized refueling hose broke loose from the airplane, and a fire erupted. The hose that separated was the inboard of two hoses attached by the refueler to the left wing refueling panel.
Investigation Findings
Examination revealed that the hose came loose due to the fracture of the three refueling adapter ring locking lugs on the airplane's inboard left wing refueling port. Metallurgical analysis of both the inboard (fractured) adapter and the outboard adapter showed that although the inboard adapter had a different microstructure and likely a different heat treatment history, both met applicable requirements for ultimate tensile strength and chemistry. The locking lug fractures resulted from a one-time ductile overstress with no preexisting cracking, corrosion, or defects that would have reduced load-carrying capacity. Therefore, the adapter failed due to an overload applied at the time of separation.
The investigation determined that the refueler had improperly positioned the hydrant truck relative to the airplane's left wing refueling panel before starting refueling. This positioning caused the lift platform's left railing to obstruct the normal nozzle attachment procedure to the inboard manifold adapter. While attaching the nozzle, the refueler improperly routed the hose over the top of the front railing, around the left forward corner support, and aft to the inboard manifold adapter ring. Evidence also indicated that the refueler lowered the lift platform for personal comfort during the long refueling, causing the hose to catch on the platform's left front railing and bumper.
Load Testing and Failure Analysis
Vertical pull tests showed that the three nozzle attachment lugs could support over 10,000 pounds when load was applied along the nozzle centerline. However, load capacity decreased as the load angle increased; at 30 degrees off centerline, the lugs failed below 1,000 pounds. The refueler's improper hose routing placed an off-axis load of approximately 52 degrees. The angular force on the manifold adapter ring increased when the refueling hose was pressurized. The combination of these two forces caused the adapter ring to fail.
Fire and Damage
Pressurized fuel discharged, forming a fuel mist cloud that subsequently ignited. The resulting fire caused fatal injuries to the refueler. The airplane sustained thermal damage to the lower leading edge panels, refueling control panel, and outboard portions of the left engine fan cowl and thrust reverser. The hydrant truck was destroyed in the fire.
Post-Accident Actions
Since the accident, two companies have introduced modifications to help position hydrant dispenser trucks during single-person operations, and industry groups are examining potential changes to existing standards and practices for aircraft fueling.