History of Flight
On August 26, 2015, about 1130 central daylight time, a Weatherly Aircraft Company 620B, registration N2005C, impacted terrain after the left wing partially separated during an aerial application flight near Hancock, Wisconsin. The pilot was fatally injured, and the airplane was destroyed. The airplane was registered to Agricair Leasing, LLC and operated by Agricair Flying Service, Inc. under Title 14 Code of Federal Regulations Part 137. Visual meteorological conditions prevailed, and no flight plan was filed. The flight originated from the operator's private airstrip near Bancroft, Wisconsin, about 1115.
A witness working in a field about half a mile from the accident site reported hearing an unusual engine sound at about 1125, followed by the sound of breaking trees. The Federal Aviation Administration (FAA) inspector determined that the airplane was performing spray operations from north to south on a potato field about 4.2 miles southeast of Hancock. The field was surrounded by trees 50 to 60 ft tall, with three birch trees about 25 to 30 ft tall near the field edge, about 30 yards closer to the planted area than the treed area. These birch trees aligned with a wreckage path containing left wing leading edge pieces, trailing edge, and wingtip, but no evidence of impact with the birch trees was found. Postaccident examination revealed damage to the left wing, spray boom, empennage, and fuselage consistent with upward and rearward separation of portions of the left wing.
Personnel Information
The pilot's logbook, as of January 2, 2015, showed 584.1 hours of total flight time in single-engine airplanes, mostly in light general aviation aircraft. In 2011, the pilot recorded only 2 flights (4.9 hours); in 2013, 3 flights (2.9 hours); and in 2014, 6 flights (6.1 hours). Agricultural flight training began in April 2015 at Battlefords Airspray in North Battleford, Saskatchewan, Canada. Training was conducted in a Gippsland GA200 and solo flights in a Piper PA-25-180 or -235. An April 28, 2015 entry indicated completion of agricultural pilot training after 26 flights for 41.2 hours.
The pilot started with Agricair Flying Service in May 2015. A desk calendar from May to August 2015 annotated flight time, loads, and acres. A Letter of Competency dated May 24, 2015 showed the pilot had satisfactorily completed knowledge and skills tests for an agricultural pilot under 14 CFR Part 137.19. By August 23, 2015, the pilot had accrued 461.1 hours of agricultural operations, including training, with 419.9 hours in the accident airplane. Daily flight times ranged from 0.4 to 13.6 hours, averaging 5.9 hours; 14 days exceeded 10 hours. No flight time was recorded for the accident day or the two preceding days.
Aircraft Information
The accident airplane, serial number 1557, was built in 1993 and registered to the operator in June 2014. It was a single-seat, single-engine, low-wing, all-metal airplane with conventional landing gear, designed for agricultural spraying. It was powered by a Pratt & Whitney R985 radial engine driving a 3-blade tractor propeller. The Weatherly 620B was certified under FAR 21.25(a) with policies in Civil Aeronautics Manual 8 (CAM 8) Appendix B.
Maintenance records showed the airplane was not flown between May 1, 2000, and March 21, 2003. Annual inspections were performed each year except 2000, 2001, and 2002. Entries for 2004-2008 and 2010-2012 noted that wing attach bolts were torqued. Wing hinge pins were inspected per Weatherly Service Note No. 15 on July 23, 1996, at 1,179 hours. On June 19, 2001, wing leading edges were removed, stripped, primed, painted, and reinstalled; two wingtip skins and two wingtip ribs were replaced. Airworthiness directives were tracked and complied with. The manufacturer's maintenance manual, Section XV, stated "Remove wing bands and inspect wing hinge fittings" but provided no other inspection details for wing hinge brackets. The most recent annual inspection was on April 15, 2015, at 4,468.9 hours; the entry stated "Removed all inspection plates & checked structure." The last maintenance entry before the accident was an oil change on August 22, 2015, at 4,811.83 hours.
Wreckage and Impact Information
The main wreckage was in a treed area beyond the southern edge of a potato field; portions were in the southwest corner of the field. The airplane struck treetops before ground impact. The left wing leading edge assembly components were found north of the main wreckage. The left outboard wing fixed trailing edge and wingtip were in grass between the planted area and treed area. Examination showed the left center section forward spar lower hinge brackets fractured vertically through the pin holes; the pin remained installed with fractured ends captured. All other spar attach points were intact. The left wing spars, interspar structure, and skins were at the main wreckage with varying damage. Mechanical damage and deformation on the left wing and center section upper spar caps adjacent to the forward spar attach point indicated the outboard wing rotated upward more than 120° relative to the center wing. The left wing rear spar fractured through the outboard wing hinge bracket holes, though brackets remained intact. The left wing structure was crushed downward between spars and curled upward, with yellow paint transfer on internal ribs. The left aileron control tubes and spray bar showed significant upward deformation.
Additional Information
The Weatherly 620B was certified with a maximum gross weight (MGW) of 4,000 lbs per certification reports; limited analysis existed at 4,800 lbs. Later manuals and marketing contained performance charts for 5,800 lbs. CAM 8 guidance allows operators to select gross weight above certificated MGW if controllability is demonstrated via flight test and documented. The most recent weight and balance report (June 22, 2004) indicated an MGW of 4,000 lbs; empty weight 3,049.29 lbs gave useful load 950.71 lbs. The operator estimated the accident flight's pre-takeoff gross weight at 5,084 lbs. No flight test record or logbook entry for increased MGW was found.
Weatherly design reports identified the critical wing structure as an aluminum reinforcement strap on the lower center section spar cap, with an MGW of 4,800 lbs. A 1993 fatigue evaluation for Australian authorities determined the forward spar outer wing hinge brackets' factored fatigue life as 5,273 hours. In August 2002, the Civil Aviation Safety Authority of Australia issued AD W620/1 Amendment 1, setting life limits of 2,500 hours for the wing main spar lower cap assembly and 5,000 hours for steel wing attachment brackets.
On March 25, 2016, the FAA issued AD 2016-07-11 for all Weatherly 201, 201A, 201B, 201C, 620, 620A, 620B, 620B-TG, and 620TP airplanes, requiring a close visual inspection of center and outer wing forward spar lower hinge brackets for cracks and corrosion within 30 days. Results were to be reported. As of the report date, FAA received information on 37 of 94 affected airplanes; no cracked brackets other than those in this investigation were reported.
Weatherly later manufactured replacement wing and center section hinge brackets from 4130 steel with cadmium plating for corrosion resistance. A service bulletin (SB) issued March 13, 2018, provided inspection and replacement instructions, with yearly corrosion inspections and a more detailed inspection every 5 years. The FAA indicated they would make the SB mandatory via an AD.
Medical and Pathological Information
An autopsy by the Fond du Lac County Medical Examiner determined the cause of death as multiple blunt force injuries. Toxicological testing by the FAA Bioaeronautical Sciences Research Laboratory was negative for ethanol, carbon monoxide, and all tested-for drugs.
Tests and Research
The NTSB Materials Laboratory examined the wing forward spar attach points. The left center section forward spar lower forward hinge bracket exhibited a visible fatigue crack with arrest marks emanating from the aft corner of the pin hole, measuring 0.15 inch on the aft face, 0.19 inch along the pin hole, and 0.24 inch deep. Scanning electron microscopy revealed fatigue striations. The crack initiation site contained a corrosion pit with non-conductive deposits. Similar corrosion pits and shallow circumferential gouging were found along the pin hole surface. The lower aft hinge bracket had rough overstress features with small fatigue cracks at the pin hole. The upper side of the aft hinge bracket showed thumbnail fatigue cracks, one initiating at an aluminum oxide inclusion. Additional microscopic fatigue cracks prompted magnetic particle inspection (MPI) of all submitted brackets. MPI found indications in the right center section forward spar lower forward hinge bracket and the left wing forward spar lower forward hinge bracket. Laboratory opening of the latter revealed multiple fatigue cracks propagating from corrosion pits.
Another Weatherly 620B (N20077, S/N 1558) with 4,337 total hours was found to have a cracked right wing forward spar lower aft hinge bracket. Examination showed the bracket had fractured through the pin hole with substantial oxidation; fatigue striations were present. Corrosion pits at crack initiation sites were noted. The lower forward hinge bracket also contained multiple fatigue cracks from corrosion pits.
Weatherly Aircraft commissioned AvSpec Corporation to perform a postaccident failure analysis. The report noted that only a static strength evaluation was performed; no dynamic, gust, or unsymmetrical loads were considered. The static strength analysis based on the known condition of the accident brackets calculated the cracked area on the lower forward face as 0.0377 in², about 15% of the bracket area.