What happened
During an approach to runway 34L at Seattle-Tacoma International Airport, a Beech 1900C experienced a sudden loss of airspeed and an increased sink rate. The pilot reported that the aircraft functioned as expected until the deployment of full flaps for landing, at which point the plane entered a stall/mush condition. The subsequent hard impact caused the nose and left-main landing gear to collapse. Following the impact, a leak in the fuel system occurred during the aircraft's slide, resulting in a post-crash fire.
Findings
Investigations into the loading process revealed that the aircraft was loaded with over 4,962 pounds of cargo during a roughly 20-minute window. Because no scale was present at the site, personnel relied on weight estimates and waybill tallies to determine the total weight and center of gravity. This period coincided with a significant increase in cargo volume for the operator due to a strike affecting a major competitor.
Post-crash analysis confirmed that the actual cargo weight exceeded the pilot's documented manifest by 656 pounds. Furthermore, the aircraft's center of gravity was found to be positioned between 6.8 and 11.3 inches beyond the aft limit. The improperly calculated weight and balance was the primary factor leading to the aerodynamic instability during the landing configuration change.