CORNING, AR, USA
N3103D
AYRES S2R-T34
The left wing of an agricultural airplane separated in flight while maneuvering during an aerial application flight. A witness observed the left wing of the airplane falling to the ground and the 'airplane cork screwing to the ground.' The left wing came to rest 90 yards from the tree line, with the main wreckage coming to rest approximately 289 yards beyond the left wing. A metallurgical examination of the fractured wing revealed that the separation of the lower spar cap was the result of a fatigue crack that emanated from the 1/4 inch diameter hole for the center splice fitting. The examination also revealed that the tensile strengths for the left wing spar cap was lower that that specified in the engineering drawing provided by the manufacturer. A review of the airframe records revealed that Ayres Service Bulletin No. SB-AG-39 ('Wing Spar Inspection and Fatigue Life Extension'), issued 17 September 1996, had not been complied with by the operator. This SB included procedures for accomplishing a magnetic particle inspection around the lower spar cap's bolt holes.
HISTORY OF FLIGHT On June 14, 1997, at 1017 central daylight time, an Ayres S2R-T34 agricultural airplane, N3103D, was destroyed following an inflight break-up while maneuvering near Corning, Arkansas. The instrument rated commercial pilot, sole occupant of the airplane, was fatally injured. The airplane, owned and operated by Hatley Flying Service of Delaplaine, Arkansas, was being operated under Title 14 CFR Part 137 at the time of the accident. Visual meteorological conditions prevailed for the local aerial application for which a flight plan was not filed. The flight originated from Delaplaine, Arkansas, at approximately 0945. The owner of the field being sprayed reported that he observed the airplane dispensing the herbicides to his rice fields in a north to south pattern. Upon completion of the third swath, the eyewitness observed the airplane initiate the pull-up to execute the turn to reverse direction over the tree line at the end of the field being sprayed. The witness added that he momentarily diverted his attention to the inside of his truck to put the vehicle in motion. When he looked up, he observed the left wing of the airplane falling to the ground and the "airplane cork screwing to the ground." The left wing came to rest 90 yards from the tree line, with the main wreckage coming to rest approximately 289 yards beyond the left wing. PERSONNEL INFORMATION The commercial pilot, age 54, certificate number 426767826, had 24 years of experience in aerial application operations. He had accumulated over 18,400 hours of flight, of which 15,000 were agricultural airplanes, with over 1,500 hours in the Ayres. His last biennial flight review (BFR) was completed in a Cessna 150 on September 1995. The pilot's most recent second class medical examination was completed on April 22, 1997. According to the pilot's medical certificate, he was required to wear corrective lenses while flying. The operator reported that this was the pilot's first season with this company, being hired in April. A friend of the pilot reported that the pilot had complained to some of his peers that in previous flights, "the airplane was making a popping sound coming from the area under the cockpit when he executed the pull up maneuver." The operator and his maintenance personnel told the NTSB investigator-in-charge (IIC) that the pilot never complained or made comments to any of them about any unusual popping sound or any other airframe defect. AIRCRAFT INFORMATION The 1990 Model Ayres S2R-T34 airplane, serial number T34-153, was purchased from Mid Continent Aircraft on April 4, 1992. The last annual inspection was performed by Turbine Aero, Inc., of Corning, Arkansas on April 21, 1997, at 4,468.9 airframe hours. The operator stated that the restricted category airplane had accumulated approximately 200 hours since the last annual inspection. The Pratt & Whitney PT6A-34AG powerplant, serial number PCE-56453, had experienced a "hot start" 3 days prior to the accident and a hot end inspection was completed on the engine the day prior to the accident. The hot end inspection was performed by Turbine Aero, Inc., of Corning, Arkansas. Optional equipment installed in the airplane were: a Wag Corporation GPS flagging system, an air conditioning system, a smoker system, and flight instruments. According to the operator, the airplane was serviced with 88 gallons of fuel prior to being loaded with a payload of 400 gallons of herbicides (Londax and Super Wakn) for aerial application flights on two fields owned by the same customer. According to the airframe maintenance records, the wings of the airplane were removed and installed by Mid-Continent Aircraft Corporation of Hayti, Missouri, on April 18, 1996, for compliance with Ayres Service Bulletin No. SB-AG-34 ("Fuselage Wing Attach Tube Beef-up"). The review of the airframe records further revealed that Ayres Service Bulletin No. SB-AG-39 ("Wing Spar Inspection and Fatigue Life Extension"), which was issued 17 September 1996, had not been complied with by the operator. This service bulletin included procedures for accomplishing a magnetic particle inspection around the lower spar cap's bolt holes. According to FAA records and the airframe logbooks, the airplane had never been involved in an accident or otherwise sustained any structural damage. An estimate of the weight of the airplane at the time of the accident placed the airplane within weight and balance limits. METEOROLOGICAL INFORMATION The nearest weather reporting station to the accident site was Jonesboro, Arkansas, located 34 miles south of the accident site. The recorded weather at 1249 reported scattered clouds at 5,000 feet, a visibility of 7 miles, with a temperature of 70 degrees and a dew point of 64 degrees. The altimeter was recorded at 29.85 inches, with winds from 340 degrees at 11 knots. The investigator-in-charge calculated the density altitude at the accident site at 1,200 feet. COMMUNICATIONS The operator was in radio contact with the pilot. No distress calls were received by the operator from the pilot. WRECKAGE AND IMPACT INFORMATION The wreckage of the airplane came to rest in a cultivated rice field to the south of the field being sprayed. The complete left wing came to rest 90 yards from the field road adjacent to the tree line. Physical evidence of the fracture and damage to the airframe and wing root area demonstrated that the left wing separated in an upward and aft direction. The main wreckage, consisting of the entire airplane less the fractured left wing and the left main tire assembly, came to rest approximately 289 yards beyond the resting place of the left wing. Ground scars were found on a measured heading of 185 degrees for approximately 82 yards from the initial point of impact to the resting place of the main wreckage. The fuselage came to rest on it's left side, on a heading of 240 degrees. There was no significant leading edge damage to the left wing. Two pieces of plexiglass identified as "side window glass" were found in the general vicinity of the left wing. Two small circular inspection panels were missing from the bottom side of the wing, one was found near the wing. Fuel was present in the left fuel cell when the wing was turned over by the investigation team to document the top side of the wing. No evidence of any tree strike was found on either wing, the propeller blades or the fuselage. The empennage of the airplane separated from the fuselage just forward of the horizontal stabilizer. Control continuity was confirmed by the NTSB IIC to the rudder, elevators, and right wing. The wing flaps were found in the retracted position. The cockpit of the airplane was destroyed by impact damage. The instrument panel was fractured in several pieces. Most engine instruments were found separated from their mounts in the instrument panel and were destroyed. All engine controls were destroyed. The engine remained attached to the engine mounts; however, the engine mounts were found separated from the airframe. The engine exhibited damage consistent with high speed rotation at impact. The 3-blade Hartzell propeller, model number HC-B3TN-T10282, was found attached to the hub; however, the engine's gear reduction case was found separated from the engine. One propeller blade was fractured approximately 6 inches from the hub. None of the propeller blades showed any evidence of impact with trees. All propeller blades had evidence of "S" bending. Approximately 40 gallons of fuel spilled from the airplane's fuel tanks. Fuel was found in both wing tanks as well as in the fuel lines to the engine. The header tank, which was found dry, was punctured and compromised in 4 places. The face of a wrist watch found in the wreckage was stopped at 1026. See the enclosed wreckage diagram for further details of the wreckage distribution. MEDICAL AND PATHOLOGICAL INFORMATION An autopsy and toxicological tests were ordered and performed. The autopsy was performed by William O. Sturner, M.D., of the Arkansas State Crime Laboratory in Little Rock, Arkansas, on June 16, 1997. Toxicological tests were performed by the FAA's Civil AeroMedical Institute (CAMI) in Oklahoma City, Oklahoma. See the enclosed toxicology report for details of their findings. SURVIVAL ASPECTS The pilot was wearing a flight helmet and gloves. The flight helmet separated from the pilot during the impact sequence. The pilot was wearing a 4-point seat belt and shoulder harness system, which was found still attached and secured to the airframe. Maintenance records revealed that the seat belts and shoulder harness had been replaced during the last annual inspection. The airplane was not equipped with an ELT. The 911 call was received at 1019. The first ambulance arrived at the scene of the accident at 1041, with a second ambulance arriving at 1119. TEST AND RESEARCH A wreckage layout and partial examination was accomplished in Clinton, Arkansas, on June 19, 1997, under the supervision of an FAA inspector. The main objective of the layout was to carefully remove both ends of the fractured spar for further examination at the NTSB laboratories in Washington, D.C. The portion of the fractured left wing forward spar was boxed and shipped to the NTSB Materials Laboratory for examination on June 25, 1997. The metallurgical examination, which confirmed that the accident airplane was equipped with steel spars and 3 layers of aluminum alloy web structure, was completed on October 28, 1997. According to the Board's metallurgist's report, the separation of the lower spar cap was the result of fatigue cracks that emanated from the 1/4 inch diameter hole for the center splice fitting. The fatigue cracking appeared to be associated with gouge and chatter marks on walls of the hole. The examination also revealed that the tensile strengths for the left wing spar cap were lower that than that specified in the engineering drawing provided by the manufacturer. See the metallurgist's report for details of the examination. The FAA aircraft certification office in Atlanta, Georgia, was notified of this occurrence by the NTSB IIC on June 17, 1997. According to FAA sources, there had been nine reported occurrences of fatigue cracking in the lower spar caps in Ayres S2R airplanes. An Emergency Airworthiness Directive (AD 97-13-11) was issued by the FAA on June 20, 1997. The AD was later amended by AD 97-17-03 to correct the designation of one of the model of airplanes affected by the emergency AD. The operator's other airplane, also an Ayres S2R-T34, serial number T34-141 was inspected as a result of this accident. A crack was found in the main spar (left wing side) using the magnetic particle inspection technique prescribed by Ayres SB-AG-39. The operator performing the non-destructive inspection (NDI) told the owner of the airplane that he found 6 cracked spars in the 15 aircraft that he had inspected up to that time. ADDITIONAL DATA The wreckage was conditionally released to the insurance adjuster for recovery and transportation to a secured location. The failed components examined by the Board's Laboratories in Washington D.C., were returned to the owner's representative. A final wreckage release was issued to the owner's representative at the completion of the investigation.
The in-flight separation of the left wing as result of fatigue crack of the lower spar cap due to inadequate materials by the manufacturer. A factor was the operator's failure to comply with a published service bulletin on the airframe.
Source: NTSB Aviation Accident Database
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