by National Transportation Safety Board

“ The fatigue propagated rearward in a low stress manner in the skin for about 1 inch. Aft of the spar area, the fracture propagated on various slant planes through the skin indicative of high stress propagation. Scanning electron microscope (SEM) examinations found that the slant region was made up of mostly ductile dimples with interspersed regions of fatigue and arrest failures. Many of the arrest features, particularly toward the aft end of the cracks were consistent with mechanical damage on the fracture due to fracture face closure and recontact. ”

“ The Forest Service conducts a pre-use inspection of the aircraft, personnel, and facilities prior to executing the airtanker contract. The Forest Service does not maintain qualified inspectors dedicated to examine the company's maintenance procedures or practices, nor do they have personnel trained and dedicated to conduct oversight inspections of air tanker operators. ”

“ According to the Airtanker Base Manager at Jeffco Airport, Broomfield, Colorado, the airplane, Tanker 123, was dispatched to join other airtankers, Tanker 161 and Tanker 22, a helitanker, number T-16, and a U. S. Forest Service lead airplane, Lead Bravo 8, to drop fire retardant on the Big Elk Fire. The airplane had flown seven previous air attack missions on the fire that day. Prior to the accident mission, the airplane was loaded with approximately 2,000 gallons of fire retardant, and 550 gallons of fuel. ”

“ The outboard section extended from Rib 16 to the wingtip, roughly 23 feet, and included the left aileron with attached trim tab. There was slashing damage to the leading edge between Ribs 19 and 20. At Rib 22, the leading edge shows circular crushing damage consistent with tree impact. The upper skin shows impact damage consistent with it impacting the ground in this orientation. The ribs observed all showed compression damage. At the separation point, the wing is bent downward and the lower skin is buckled and bent downward. ”

“ The ring cowling was crushed aft. The bottom cowling was crushed inward and aft. The engine was intact and remained connected to the wing by fuel and oil lines and control cables. The number 2 propeller showed two of the three blades still mounted in the hub. The first blade was straight and showed chordwise scratches along the leading edge and the blade face. The second blade was bent rearward along the bottom engine cowling and twisted outboard. The third blade was broken out of the hub and found resting on the ground approximately 10 feet east of the inboard wing section. ”

“ Inspect right wing for cracks, deformation, damaged, loose or missing fasteners. 2.) Inspect lower side of wing inboard for evidence of fuel leaks,
"C" Service and Inspection Guide, Left Wing and Nacelles, Item 1, Left Wing (Right Wing items reads the same) : 1.) Perform detailed inspection of wing for cracks, corrosion, deformation, damage, loose, missing and defective fasteners.
Item 4, Wing Structure reads: 1.) Detailed inspection of wing to fuselage attach fittings and bolts.
Item 9, Wing Spar reads: 1.) Inspect in detail forward and aft spar at wheel well area for corrosion and cracks. ”

“ Splice the insertion in place by the use of angles or plates, as applicable. Splices should cover the entire filler if it is less than eight inches in length. For fillers longer than eight inches, splice at the butted ends only. ”

“ The airplane is then shown making a left turn and rolling out on a 195-degree heading. The airplane remains on this heading for 0.6 nautical miles, when radar contact is lost. The accident site was approximately 0.1 nautical miles southwest of the last radar plot.
PERSONNEL INFORMATION The pilot-in-command held a commercial pilot license with single and multiengine land, instrument airplane ratings, dated January 17, 1996. The pilot was type-rated in CV-P4Y airplanes. The pilot also held a flight instructor certificate with endorsements for instruction in single-engine land airplanes. ”