N2283M

HISTORY OF FLIGHT

On June 10, 2016, about 0900 eastern daylight time, an experimental WSK PZL MIELEC M-18A, N2283M, was destroyed following an inflight separation of the right wing while maneuvering near Brunswick, North Carolina. The commercial pilot was fatally injured. Visual meteorological conditions prevailed, and no flight plan was filed for the aerial application flight, which was operated by Canam Aviators Inc., under the provisions of Title 14 Code of Federal Regulations Part 137. The flight originated from Bear Pen Airstrip (NC43), Supply, North Carolina, around 0845.

According to ground personnel, the airplane departed with a full load of fertilizer and 45 minutes of fuel with 30 minutes of reserve fuel. After 1 hour passed and the airplane did not return to the airport, ground personnel called 911 to report the airplane missing. The airplane was subsequently located in a wooded area.

PERSONNEL INFORMATION

According to Federal Aviation Administration (FAA) records, the pilot held a commercial pilot certificate with ratings for airplane single-engine land, airplane multiengine land, instrument airplane, and rotorcraft-helicopter. He also held an FAA second-class medical certificate, which was issued on May 13, 2016. At the time of the medical examination, the pilot reported 30,576 total hours of flight experience. The pilot's logbook was not recovered.

AIRCRAFT INFORMATION

The airplane was manufactured in 1994 and imported to the US, where it was issued a special airworthiness certificate in the restricted category. The accident operator purchased the airplane in 2003.

The most recent annual inspection was performed on January 15, 2016, at 8,567.9 hours total time in service. All of the inspection and maintenance entries from October 17, 2012, to the time of the accident were performed by the same company and mechanic. There were four annual inspections completed in this timeframe, and all entries specified that the inspections were conducted in accordance with the M-18 Service Manual. There was no specific information to indicate which of the published inspections from the manual were performed.

The airplane wing is composed of three sections; the center section and the right and left outboard sections. The outboard wing sections are connected to the center wing at three points each: two on the forward spar and one on the aft spar. The center section contains clevis fittings at the forward spar upper and lower spar caps and a clevis fitting at the aft spar. Corresponding lug fittings on the outboard wing sections fit into the center wing clevis fittings. The forward spar connections use an expansion mandrel installed through the bores of the center wing clevis and wing lug fittings. The aft spar connection uses a bolt installed through the bores of the center wing clevis and wing lug fittings.

An FAA inspector estimated that the takeoff weight was about 11,787 lbs, using an airplane empty weight of 5,975 lbs, chemical weight of 4,940 lbs (800 gallons), a fuel weight of 692 lbs (1.5 hours), and a pilot weight of 180 lbs.

AIRPLANE MODIFICATION AND MAINTENANCE HISTORY

The type certificate for the PZL M-18A was approved by the FAA in September 1987. The maximum weight was 9,260 lbs with a maximum hopper weight of 3,300 lbs regardless of the hopper capacity.

The original engine was removed from the accident airplane in April 1996 and replaced with a Honeywell TPE 331 turbine engine driving a Hartzell 3-blade, constant speed, reversing and feathering propeller in accordance with STC SA09039SC. Geared servo tabs were installed on the ailerons, elevators, and rudder in accordance with STC SA09063SC as part of the engine conversion. At the time of the modification, the airplane had accrued 997.0 hours total time in service. The airplane was again modified in January 2005, in accordance with STC SA09039SC, to install a different Honeywell TPE331 turbine engine driving a Hartzell 5-blade constant-speed reversing and feathering propeller. The airplane had accrued 5,153.7 hours total time in service at the time of this modification. The maximum weight approved as part of the STC was 9,260 lbs with the spray bar installed and 8,800 lbs with the spreader installed. A modified hopper was also installed at this time, which increased the hopper capacity to 800 gallons.

A logbook entry at an airframe time of 6,389.0 hours on June 21, 2006, indicated that the service life of the airplane was increased to 10,000 hours by incorporation of a manufacturer service bulletin. An entry on October 9, 2009, adjusted the total time in service of the airframe from 7,630 hours to 6,147 hours. The explanation provided in the entry indicated that the hour meter installed was recording incorrectly. On February 20, 2014, at an airframe time of 8,042.0 hours, a logbook entry documented the replacement of both left lower wing attach fittings and expanding mandrel in accordance with SB E/02.170/2000. On July 2, 2015, a logbook entry documented the replacement of the wing center section with a used serviceable unit with an estimated total time of 7,460 hours; the airframe time was 8,562.9 hours.

WRECKAGE AND IMPACT INFORMATION

Examination of the wreckage by an FAA inspector revealed that the debris path was oriented from south to north. The wreckage area was compact except for the right wing and one propeller blade, which were located about 125 ft east of the main wreckage. The airplane impacted in a nose-down attitude of about 60°. The left wing was located on top of the engine and separated from the fuselage. The fuselage, cockpit, and hopper were found 10 ft north of the initial impact point. The remainder of the empennage was found 20 ft north of the cockpit. Small pieces of debris were found within a 50-ft radius of the initial impact point.

Further examination of the airplane by an NTSB investigator revealed that the right outboard wing forward spar lower fitting was fractured. Additionally, the right outboard aileron attach bracket was fractured, and visible cracks were evident on the right center and inboard aileron attach brackets. The fractured wing fitting, a fractured wing fitting attach bolt, and all three aileron attach brackets were sent to the NTSB Materials Laboratory Division in Washington, D.C. for analysis.

ADDITIONAL INFORMATION

Metallurgical Examination

The right outboard wing forward spar lower fitting fractured through the upper and lower arms in the areas indicated by arrows in figure 1. Each arm contained six vertical bolt holes used to attach the fitting to the outboard wing forward spar. The fracture in the upper arm intersected the inboard vertical bolt hole, and the fracture in the lower arm intersected the second vertical bolt hole from the inboard end. Bench binocular microscope of the fractured arms revealed all the fracture faces contained fatigue cracks that emanated from the bore of the holes on diametrically opposite sides of each hole, in the areas indicated by brackets "O" in figure 1.

Figure 1. Right outboard wing forward spar, lower fitting.

Figure 2 shows a photograph of the lower arm fracture faces. The fatigue cracks in the lower arms initiated from multiple origins along the entire length of the bolt hole, in the areas indicated by brackets "O" in figure 2. Most of the fatigue crack origins were associated with corrosion pitting in the bore. Fatigue propagation on each side of the hole was through a 90% of the thickness and terminated in the areas indicated by dashed lines in figure 2.

Figure 2. Right outboard wing forward spar, Lower fitting, Lower arm.

Figure 3 shows a photograph of the upper arm fracture faces. The upper arm fractures contained similar fatigue cracks with the exception that the fatigue cracks initiated from multiple origins near the lower portion of the bolt hole. Most of the fatigue crack origins were associated with corrosion pitting in the bore. The fatigue cracks in the upper arms exhibited better defined fatigue fracture features than those on the lower arms.

Figure 3. Right outboard wing forward spar, lower fitting, upper arm.

The fractured bolt examined was installed through the third vertical bolt hole in the right outboard wing forward spar lower fitting. The fracture intersected the root thread portion of the bolt. The fracture face of the bolt contained fatigue cracks that emanated from multiple origins all around the root portion. Fatigue propagation was toward the center of the bolt and extended through about 95% of the bolt cross section.

Figure 4 shows a photograph of the right outboard aileron attach bracket, which contained a circumferential fracture in the main tube portion, near the location where the two upper arms were welded to the main tube. The fracture intersected the aft edges of the welds at the base of the two arms, indicated by arrows "X" in figures 4. Bench binocular microscope examination of the forward face of the main tube fracture revealed multiple fatigue cracks that emanated from the outer surface of the main tube at the aft edges of the welds. Fatigue propagation was through about 50% of the thickness and extended around about 30% of the tube circumference. Corrosion was noted on the outboard tube surface.

Figure 4. Right outboard aileron attach bracket.

The right center and inboard aileron attach brackets were intact, but both brackets contained visible cracks in the white paint layer where the two upper arms were welded to the main tube. The paint was removed with a commercial paint stripper from the weld areas of the intact brackets. Bench binocular microscope examination of both intact brackets after paint stripping revealed the presence of corrosion and intermittent cracks on the outer surface of the welds in the same respective location as the fracture on the outboard bracket. The cracks were not opened, but examination of the inner face of the main tube portion for both intact brackets reveal...