The pilot of an air taxi that crashed on Alaska's Kenai Peninsula in 2013, killing all 10 people on board, underestimated the weight of the plane's cargo, the National Transportation Safety Board said in a report issued Wednesday.

The probable cause of the crash was the operator's failure to account for about 420 additional pounds of unspecified cargo, which led to loading and operating the de Havilland DHC3 Otter outside its weight and center-of-gravity limits, the report said

An extensive postcrash fire consumed most of the airplane's cockpit and cabin area, including an unknown quantity of the baggage and cargo.
The investigation found that the flaps were set to the full-down (or landing) position during takeoff, contrary to recommended procedures in the airplane flight manual (AFM).
Thus, based on the investigation's best estimate and a calculation of the airplane's weight and balance using the recovered passenger weights, weights and location of the luggage recovered on scene, weight of the cargo recovered on scene, and weights accounting for the liquid cargo destroyed in the postimpact fire, once the passengers were loaded, the airplane weight would have exceeded the maximum gross weight of 8,000 lbs by about 21 lbs and the CG would have been at least 5.5 inches aft of the 152.2-inch limit (a more definitive calculation could not be performed because the exact location of the cargo was not known).