History of Flight
On February 28, 2014, about 0955 Pacific standard time, a Grumman G164-A Ag-Cat, registration N72ES, was substantially damaged during landing at a private agricultural airstrip in Caruthers, California. The airplane was owned and operated by Trinkle Ag Flying of Kingsburg, California. The pilot was not injured. The flight was conducted under Title 14 Code of Federal Regulations Part 137 as an aerial application flight. Visual meteorological conditions prevailed, and no FAA flight plan was filed.
The pilot reported that the flight was the third of the day, applying fertilizer. Upon touchdown to the north, he heard a "huge bang," and the airplane began to roll right wing down. He attempted to correct with aileron but was only partially successful. The airplane decelerated, veered right after the right wing contacted the ground, and departed the paved surface. As it descended the embankment, the propeller struck the ground, and the airplane nosed over. It came to rest inverted, partially down the embankment and mostly off the runway. No fire or fertilizer spill occurred.
Personnel Information
The pilot held a commercial pilot certificate with an airplane single engine land rating. He reported approximately 2,434 total flight hours, including about 1,943 hours in the accident airplane make and model. His most recent flight review was completed in September 2012, and his most recent FAA second-class medical certificate was issued in March 2013.
Aircraft Information
The airplane was manufactured in 1972 and equipped with a Pratt & Whitney R-985 series engine. According to operator records, total time in service was about 16,615 hours, and the failed landing gear leg had about 6,000 hours. The most recent 100-hour inspection was completed in November 2013. FAA records indicated the airplane serial number was 758. Examination revealed that a dataplate on the rudder post fairing bore serial number 1710, but another dataplate behind the cockpit bore the correct serial number. The FAA inspector noted that when an operator owns multiple aircraft of the same type, parts can be mixed up.
Meteorological Information
The 0953 automated weather observation at Fresno Yosemite International Airport, about 15 miles north, included winds from 130 degrees at 18 knots, visibility 10 miles, few clouds at 3,500 feet, scattered at 15,000 feet, broken at 20,000 feet, temperature 17°C, dew point 13°C, and altimeter 29.55 inches of mercury.
Wreckage and Impact Information
The airplane came to rest inverted adjacent to the east side of the runway. The upper wing, fuselage, fin, and rudder sustained substantial crush or bending deformation. The right main landing gear leg was fracture-separated near the fuselage juncture, and the left wheel assembly was fracture-separated from the left main landing gear leg.
Additional Information: Landing Gear Leg Fracture Evaluation
Examination by NTSB Materials Laboratory personnel revealed that the fracture face indicated primarily a fatigue crack that progressed to instantaneous failure. The fracture face was covered by rust products except at the lower forward corner, where a semi-elliptical region was nearly rust free. Fracture traces and markings indicated fracture initiation in the clean region. Optical inspection revealed a small, darkly oxidized semi-elliptical region adjacent to the lower gear surface at the forward corner, surrounded by a cleaner region about 0.4 inch wide by 0.25 inch high. One crack arrest band was visible, and shear lips were evident.
Optical examination of the surface adjacent to the oxidized region revealed chipped yellow paint with a rough, rusted underlying surface. Removal of more paint uncovered an eroded and globular surface, consistent with localized melting and resolidification from electrical arcing. Damage dimensions indicated a single sustained large arc on the lower surface and two separate arcs on the upper surface. X-ray energy dispersive spectroscopy showed elements consistent with plain carbon steel.
The fatigue crack originated at the site of preexisting electrical arc damage, which created a local hard spot. The gear progressively cracked, first to the extent of the oxidized region, then through the first transgranular band, and finally to the clean region. Paint on the arc damage surface indicated that the damage occurred prior to paint application. The chipped paint and corrosion were consistent with paint not applied recently.
The manufacturer's instructions contained a caution that landing gear legs are heat treated and no welding is permissible. Possible mechanisms for arc damage included a power line strike, lightning strike, improper grounding during weld repairs, or processing damage during overhaul. Maintenance records were not available, preventing determination of the likely mechanism or date and precluding identification of inspection interval or process deficiencies.