Loading
The Beech 1900C cargo aircraft was loaded with more than 4,962 pounds of cargo over approximately 20 minutes. No scale was available at the aircraft, forcing loaders to rely on tallying waybill weights or estimates of total cargo weight and center of gravity (CG). Additionally, a strike had shut down a major cargo competitor, leading to substantial cargo overflow to the operator.
Post-crash examination determined that the actual cargo load was 656 pounds greater than documented on the pilot's load manifest, and the CG was between 6.8 and 11.3 inches aft of the aft limit.
Flight and Landing
According to the pilot, the airplane behaved normally until he initiated full flaps for landing approaching the threshold of runway 34L at Seattle-Tacoma International Airport. At that point, the aircraft's airspeed began to decay rapidly and a high sink rate developed as the aircraft entered a stall/mush condition.
The aircraft then landed hard, overloading the nose and left-main landing gear, which collapsed.
Post-Impact Fire
During the ground slide, a post-impact fuel system leak led to a post-crash fire.