# NTSB CHI97LA004: Bell 47G-5, N7925J, Nunda, SD, October 6, 1996 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: October 6, 1996, 08:00 local (13:00 UTC) - Place: Nunda, SD - Coordinates: 44.159339, -97.010368 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=44.1593&lon=-97.0104&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report September 30, 1997 - Report: Approved by Office Director - NTSB case key (mKey): 10473 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CHI97LA004 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/10473/pdf - Page: https://openairdocs.org/ntsb/CHI97LA004 ## Probable cause failure of maintenance personnel to properly torque the six accessory drive bolts, which resulted in fatigue failure of the undertorqued bolts. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Loss of engine power(total) - mech failure/malf, maneuvering - aerial application - accessory drive assy - undertorqued (cause) - maintenance,overhaul - inadequate, other maintenance personnel (cause) - accessory drive assy - fatigue (cause) - Forced landing, emergency descent/landing - autorotation - performed, pilot in command - In flight collision with terrain/water, emergency landing ## Analysis During the second agricultural load, a total loss of engine power occurred, and the pilot made an autorotative landing, but the helicopter was damaged during the occurrence. Examination of the engine revealed failure of six bolts that attached the accessory drive gear to the crankshaft. Further examination of the attachment bolts revealed that fatigue cracking had occurred. There was evidence that inadequate pre-load torque had been applied to the assembly. The engine had approximately 400 hours since its last overhaul. ## Factual narrative On October 6, 1996, at 0800 central daylight time (cdt), a Bell 47G-5, N7925J, registered to Wayne Hursey Aerial Blades, of Flandreau, South Dakota, piloted by a commercial helicopter pilot, was substantially damaged following a loss of engine power and subsequent autorotion near Nunda, South Dakota. The pilot reported no injuries. The 14 CFR Part 137 flight was operating in visual meteorological conditions. No flight plan was on file. The flight departed Flandreau Airport, Flandreau, South Dakota, at 0640 cdt. According to the pilot's written statement he was flying his second agricultural chemical load that morning when the engine loss total power. The pilot successfully autorotated the helicopter. Post accident examination of the helicopter by a Federal Aviation Administration Principal Maintenance Inspector (PMI), stated that a teardown of the engine revealed six sheared accessory drive gear bolts. The six attachment bolts, three lock plates, three dowel pins, shaft assembly and the accessory drive gear were sent to the NTSB's Materials Laboratory for further examination. The attachment bolts for this assembly separated at the thread area located between approximately 0.1 and 0.3 inches below the lower surface of the bolt head. Fragments of these bolts were found attached to the accessory drive gear. The surface of the shaft facing the lock plates contained fretting damage all around the bolt through holes. The dowel pin through holes on the shaft contained elongation damage and the diameter surface of each dowel pins was severely burnished. No cracking was found on the shaft, accessory drive gear, and dowel pins. This engine assembly separated 400 hours since the last overhaul. The metallurgist's factual report is enclosed with this report. ## Aircraft - Registration: [N7925J](https://openairdocs.org/aircraft/N7925J), registered now, S/N 25041, built 1971 (OpenAirDocs) - Reported make and model: Bell 47G-5 - Registry model: [Bell 47G-5](https://openairdocs.org/model/bell-47g-5) (registry code 1181032) (OpenAirDocs) - Registry engine: [Lycoming VO-435 series](https://openairdocs.org/engine/lycoming-vo-435-series) (registry code 41525, reciprocating) (OpenAirDocs) - Category: Helicopter - Serial number: 25041 - Airframe hours: 5546 - Engines: Lycoming VO-435-A 260 horsepower reciprocating - Damage: Substantial damage - Flight: Aerial application, Part 137 - Registered owner: Wayne Hursey Areial Blades - Airworthiness certificate: Special, Restricted (Special); Standard, Normal - Last inspection: Annual, April 15, 1996, 426 hours before - Departed: SD18, FLANDREAU, SD ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 26; commercial; airplane ratings: single-engine land; medical: class 2, valid medical--w/ waivers/lim; seat: left; flight hours: 2,600 total, 1,100 in this make and model, 2,488 as pilot in command, 320 in the last 90 days, 160 in the last 30 days, 1 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 340° at 7 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 48 °F, dew point 43 °F - Altimeter: 30.00 inHg - Observed at: BKX ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Accident 19961006031079A](https://openairdocs.org/incident/19961006031079A), Oct 6, 1996: Bell 47G5, Nunda, SD, Substantial damage. Aircraft engine failed during aerial application and aircraft crashed in the field. (-23) no narrative. (.4) during the second agricultural load, a total loss… ## Other investigations on N7925J (3) From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. - [NTSB CHI03LA210](https://openairdocs.org/ntsb/CHI03LA210), Jul 15, 2003: Bell 47G-5 (N7925J), Cleveland, MN, destroyed. Probable cause: The pilot's inadequate visual lookout and low altitude flight when he failed to maintain altitude/clearance from the transmission wire. A factor contributing to the accident was the transmission wire. - [NTSB MIA93LA027](https://openairdocs.org/ntsb/MIA93LA027), Dec 7, 1992: Bell 47-G5A (N7925J), Belle Glade, FL, substantial damage. Probable cause: THE IMPROPER IN FLIGHT DECISION OF THE PILOT IN COMMAND TO ATTEMPT AN AGRICULTURAL TURN WITH INSUFFICIENT ALTITUDE TO ACCOMPLISH THE MANEUVER. CONTRIBUTING TO THE ACCIDENT WAS THE PILOT'S… - [NTSB MIA91TL#03](https://openairdocs.org/ntsb/MIA91TL%2303), Mar 27, 1991: Bell 47-G5A (N7925J), Titusville, FL, substantial damage From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.