N96195

HISTORY OF FLIGHTOn July 6, 2018, about 1720 eastern daylight time, a Bell 47G-2 helicopter, N96195, was substantially damaged when it impacted a corn field near Arlington, Indiana. A postimpact fire ensued. The commercial pilot was fatally injured. The helicopter was owned and operated by Central Indiana Ag Services, LLC as a Title 14 Code of Federal Regulations Part 137 aerial application flight. Visual meteorological conditions prevailed and no Federal Aviation Administration (FAA) flight plan had been filed for the flight. The local flight departed about 1655 from a loading platform at a farm located 1 mile northwest of the accident location.

According to the co-owner of the helicopter, the pilot had been flying since 0945 that morning and had completed between 10 and 15 spray runs. The pilot was applying a fungicide to corn crops and each run was averaging 20 minutes. When the pilot did not return after 30 minutes, they initiated search operations. The wreckage was located later that evening.

Figure 1 shows the flight track for the accident flight based on GPS latitude and longitude data recovered from a Lowrance AIRMAP 2000c device installed on the helicopter. The device contained data from three flight tracks; one of which was the accident flight. The data did not contain altitude or time data, so the time lengths of the track are not known. The last data point of the final flight recorded was consistent with the wreckage location.

There were no witnesses to the accident.

Figure 1. Accident Flight Track from Lowrance Airmap AIRCRAFT INFORMATIONLimited maintenance records were provided to FAA inspectors and subsequently, National Transportation Safety Board (NTSB) investigators. A review of the available maintenance records indicated that an annual inspection had been completed on February 15, 2018, at an airframe total time of 13,922 hours. The Hobbs Meter on scene read 323.8. The helicopter flew approximately 26.8 hours between the last inspection and the accident and had a total airframe time of 13,948.8 hours.

On July 9, 2009, the main rotor transmission was replaced with another transmission. A maintenance release card for the main rotor transmission, dated June 24, 2009, revealed that the fan drive quill and the clutch assembly were repaired with serviceable parts in accordance with Bell 47G-2 maintenance procedures. The transmission was tested and reinstalled "in accordance with the manufacturers publications and FAR part 43." The work orders associated with this replacement confirmed this information.

The maintenance records contained only two entries indicating routine annual/100-hour inspections between July 2009 and January 2014. A maintenance log entry dated November 1, 2014, stated in part "retorqued transmission T adapter plat bolts." This maintenance was performed during a 100-hour inspection at an airframe total time of 13,875.2 hours. The mechanic that performed this work was no longer available to speak to investigators. No other entries in the available maintenance records noted work on the main rotor transmission.

According to the co-owner of the helicopter, on the day before the accident, he and the pilot performed general maintenance on the helicopter. The co-owner's description of the maintenance performed did not include any reference to work on the main rotor transmission.

According to the Illustrated Parts Breakdown (IPB) document for the Bell 47G-2 helicopter as provided by a representative of Scott's Bell, Inc., the attachment bolts holding pieces of the main rotor transmission housing together consist of 6 AN5-37A bolts, 1 AN5-41A bolt, and 1 AN5-44A bolt. The AN5-41A and AN5-44A bolts are located next to each other. Each of the bolts in the IPB has a NAS679A5 nut. The 6 AN5-37A bolts are each installed with 1 AN960-516 washer under the head and 1 AN960-516L washer under the nut. The AN5-41A and AN5-44A bolts are each installed with 1 AN960-516 washer under the head and another AN960-516 washer under the nut. AIRPORT INFORMATIONLimited maintenance records were provided to FAA inspectors and subsequently, National Transportation Safety Board (NTSB) investigators. A review of the available maintenance records indicated that an annual inspection had been completed on February 15, 2018, at an airframe total time of 13,922 hours. The Hobbs Meter on scene read 323.8. The helicopter flew approximately 26.8 hours between the last inspection and the accident and had a total airframe time of 13,948.8 hours.

On July 9, 2009, the main rotor transmission was replaced with another transmission. A maintenance release card for the main rotor transmission, dated June 24, 2009, revealed that the fan drive quill and the clutch assembly were repaired with serviceable parts in accordance with Bell 47G-2 maintenance procedures. The transmission was tested and reinstalled "in accordance with the manufacturers publications and FAR part 43." The work orders associated with this replacement confirmed this information.

The maintenance records contained only two entries indicating routine annual/100-hour inspections between July 2009 and January 2014. A maintenance log entry dated November 1, 2014, stated in part "retorqued transmission T adapter plat bolts." This maintenance was performed during a 100-hour inspection at an airframe total time of 13,875.2 hours. The mechanic that performed this work was no longer available to speak to investigators. No other entries in the available maintenance records noted work on the main rotor transmission.

According to the co-owner of the helicopter, on the day before the accident, he and the pilot performed general maintenance on the helicopter. The co-owner's description of the maintenance performed did not include any reference to work on the main rotor transmission.

According to the Illustrated Parts Breakdown (IPB) document for the Bell 47G-2 helicopter as provided by a representative of Scott's Bell, Inc., the attachment bolts holding pieces of the main rotor transmission housing together consist of 6 AN5-37A bolts, 1 AN5-41A bolt, and 1 AN5-44A bolt. The AN5-41A and AN5-44A bolts are located next to each other. Each of the bolts in the IPB has a NAS679A5 nut. The 6 AN5-37A bolts are each installed with 1 AN960-516 washer under the head and 1 AN960-516L washer under the nut. The AN5-41A and AN5-44A bolts are each installed with 1 AN960-516 washer under the head and another AN960-516 washer under the nut. WRECKAGE AND IMPACT INFORMATIONThe wreckage was located at the south end of a corn field at an elevation of 850 ft. The initial impact point was characterized by damage to the crop, just north of the edge of the field. The initial damage swath/scar was 20 ft long and 6 ft at its widest point. The helicopter impacted on an approximate bearing of 002° and the wreckage came to rest inverted about 20 ft from the initial impact point.

The main wreckage of the helicopter included the fuselage, landing skids, engine and lower transmission assembly, tail rotor, and tail boom. A postimpact fire damaged the left side of the fuselage and engine.

The upper portion of the helicopter, to include both main rotor blades, the mast, collective and cyclic controls, swash plate, and upper portion of the transmission were located about 75 ft north of the main wreckage. The components remained together as an assembly.

The lower portion of the transmission assembly remained attached to the engine. The internal gears of the transmission rotated freely when actuated at the engine and the tail rotor spline. A large scar/witness mark was observed on the inside well of the transmission. The mounting holes on the lower housing of the transmission were labeled Nos. 1 through 8 for identification purposes (Figure 2). The Nos. 1 and 7 holes were torn and partially separated. The Nos. 2 and 3 holes were unremarkable. The Nos. 4 and 5 holes were elongated. The Nos. 6 and 8 holes were elongated, and the hole material exhibited tearing on the outer edge. No fasteners remained in any of the holes.

Figure 2. Lower Transmission With Labels 1 through 8

The upper portion of the transmission assembly remained attached to the main rotor assembly. The attachment locations where the upper portion separated from the lower portion were labeled Nos. 1 through 8 for identification purposes and corresponded with the lower portion of the transmission. Bolt Nos. 1 and 7 remained inserted and both the metal from the adjacent mounting surface and the nut remained attached. Bolts Nos. 2 and 3 remained inserted and neither bolt remained attached to a nut. Bolts Nos. 4, 5, and 6 remained partially inserted and neither bolt remained attached to a nut. Bolt No. 8 remained inserted and was bent at the thread end and no nut was attached.

The upper portion of the main rotor transmission assembly and the eight attachment bolts were sent to the NTSB Materials Laboratory in Washington, DC, for further examination.

A washer was observed under the head of each of the attachment bolts Nos. 1, 2, 7, and 8. A washer was also included with attachment bolt No. 4, but not with bolt Nos. 3 and 5. Bolts Nos. 1 and 7 had nuts remaining in place on the threaded end of the bolt, and 2 washers were observed under the nut on each bolt. The thickness of all remaining washers except for the one under the head of attachment bolt No. 7 was approximately 0.060 inch, consistent with an AN960-516 washer. The washer under the head of attachment bolt No. 7 was about one-half the thickness of the other washers, consistent with an AN960-516L washer.

On the lower surface of the freewheeling gear where it mated to the lower transmission housing, areas of slight fretting damage and material transfer were observed near attachment bolt holes Nos. 3 through 8. The lower edge of attachment bolt hole No. 5 was deformed inward consistent with contact with the attachment bolt grip.

The attachment bolts had varying numbers of i...