# NTSB CHI08LA211: Bell 47G-4A, N24HM, Mayville, WI, July 24, 2008 - Type: NTSB accident investigation - Classification: Accident · Fatal · Limited investigation · Final report - Date: July 24, 2008, 06:52 local (11:52 UTC) - Place: Mayville, WI - Coordinates: 43.490978, -88.540618 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=43.4910&lon=-88.5406&mi=10 - Phase of flight: [Standing](https://openairdocs.org/ntsb-phases/150) (OpenAirDocs' grouping) - Defining event: [Standing-engine(s) operating: AC/prop/rotor contact w person](https://openairdocs.org/ntsb-events/081) - Highest injury: Fatal - Injuries: 1 fatal - Status: Completed, report September 30, 2009 - Report: Approved by Office Director - Parties: Federal Aviation Administration - NTSB case key (mKey): 68659 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CHI08LA211 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/68659/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=68659 - Page: https://openairdocs.org/ntsb/CHI08LA211 ## Probable cause The pilot's failure to maintain clearance with the rotating rotor blades after he exited the helicopter after landing. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Attention/monitoring](https://openairdocs.org/ntsb-findings/02021500): Personnel issues › Psychological · Pilot (probable cause); cases with it: [Bell 47G-4A, 1 case](https://openairdocs.org/ntsb-findings/02021500/cases.md?model=1181031), [All aircraft, 18 cases](https://openairdocs.org/ntsb-findings/02021500/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Standing-engine(s) operating: AC/prop/rotor contact w person](https://openairdocs.org/ntsb-events/081) (defining event); cases with it: [Bell 47G-4A, 1 case](https://openairdocs.org/ntsb-events/081/sequence.md?model=1181031), [All aircraft, 61 cases](https://openairdocs.org/ntsb-events/081/sequence.md) ## Analysis A witness heard the engine running rough when the agricultural application helicopter took off, adjacent to the field that was going to be sprayed. The pilot then landed the helicopter in the field which had tall vegetation and uneven terrain. The left skid separated during landing resulting in the helicopter resting left side low. The pilot then exited and walked around the helicopter when he was struck by the rotating main rotor blades and was fatally injuried. Examination of the engine revealed an exhaust valve that displayed excessive wear which would result in the engine running rough due to the valve sticking. Logbook records show that the engine and parts manufacturer approval (PMA) manufacturer's recommended maintenance had not been performed. ## Factual narrative On July 24, 2008, about 0652 central daylight time, the pilot of a Bell 47G-4A, N24HM, received fatal injuries when he was stuck by the main rotor blade while exiting the helicopter near Mayville, Wisconsin. The pilot had shut down the engine and exited to inspect the helicopter. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 137 agricultural application flight was not operating on a flight plan. The ground loader heard the engine running rough when the helicopter took off next to the field that was going to be sprayed. The helicopter flew in a southerly direction for about 200 yards before landing. During landing, the left skid became entangled in the surrounding vegetation and the helicopter turned towards the north breaking off the left skid. The helicopter landed in a field about 3/8 mile from the loading site and was resting left side low. The pilot exited and walked around the helicopter with the main rotor blades still rotating. The pilot was then fatally injured when he was struck by the rotating blades. AIRCRAFT INFORMATION The helicopter was powered by a Lycoming VO-540-B1B3 engine, serial number L-2450-43, that had a total time in service of 3,378.6 hours and a total time since overhaul of 395 hours. There were no markings identifying all the cylinder heads and barrels as Parts Manufacturer Approval (PMA) parts. The return to service tags associated with the engine cylinder assemblies were not received by the National Transportation Safety Board or Federal Aviation Administration (FAA). Textron Lycoming Mandatory Service Bulletin 388 calls for 300-hour interval inspections if engine valve sticking is suspected. Also, Engine Components, Inc. (ECI) Service Instruction 03-11, which references Textron Lycoming Service Bulletin 388 also calls for similar inspections on ECI Titan Cylinder assemblies. There were no engine logbook entries showing that such inspections were performed. The maximum gross weight of the helicopter was 3,200 lbs and the operator reported weight at the time of the accident was 3,100 lbs. The helicopter was loaded with 80 lbs of chemical applicant. MEDICAL AND PATHOLOGICAL INFORMATON An autopsy of the pilot was conducted by the Dodge County Medical Examiner on July 24, 2008. The cause of death was listed as blunt force trauma. The FAA's Final Forensic Toxicology Fatal Accident Report on the pilot states that no carbon monoxide was detected in blood, no cyanide was detected in blood, no ethanol was detected in blood, metoprolol was detected in blood and urine, and naproxen was detected in urine. TESTS AND RESEARCH A compression check of the engine revealed that the number one cylinder had a compression ratio of 45/80 with an exhaust valve leak. The number one cylinder assembly contained Superior Air Parts, Inc. Nimonic exhaust valve, part number SL16470AK, and Engine Components, Inc. (ECI) exhaust valve guide, part number AEL 75838 P030. The exhaust valve exhibited four fractures and a relative burnt appearance. The valve guide displayed excessive wear (bell-mouthing). The exhaust valve had an outside diameter of 0.496 inch; the exhaust valve guide interior diameter was 0.540 inch, and a clearance 0.044 inch (0.006 inch nominal). Comparative examination of the number three cylinder exhaust valve also showed a burnt and worn appearance but to a lesser degree than the number one cylinder. No visible cracks of the exhaust valve were noted. ## Aircraft - Registration: [N24HM](https://openairdocs.org/deregistered/N24HM-2024-04-26), registration cancelled 2024-04-26, S/N 7688, built 1970 (OpenAirDocs) - Reported make and model: BELL 47G-4A - Registry model: [Bell 47G-4A](https://openairdocs.org/model/bell-47g-4a) (registry code 1181031) (OpenAirDocs) - Registry engine: [Lycoming VO-540 series](https://openairdocs.org/engine/lycoming-vo-540-series) (registry code 41534, reciprocating) (OpenAirDocs) - Category: Helicopter - Serial number: 7688 - Airframe hours: 10775 - Engines: Textron Lycoming VO-540-B1B3 300 hp reciprocating - Damage: Minor damage - Flight: Aerial application, Part 137 - Operator: Reabe Flying Service - Registered owner: McCraw Enterprises Inc. - Airworthiness certificate: Special, Restricted (Special) - Last inspection: Annual, November 1, 2007 - Departed: Mayville, WI - Destination: Mayville, WI ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 70; injuries: fatal; commercial, airline transport, flight instructor; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 2, with waivers/limitations; last flight review January 21, 2008; seat: left; toxicology performed; flight hours: 24,000 total, 16,000 in this make and model, 24,000 as pilot in command, 56 in the last 90 days, 56 in the last 30 days, 4 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 180° at 2 knots - Visibility: 10 statute miles - Lowest ceiling: 4,000 ft overcast - Temperature: 61 °F - Altimeter: 30.05 inHg ## 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 20080724850309A](https://openairdocs.org/incident/20080724850309A), Jul 24, 2008: Bell 47G4A, Mayville, WI, Minor damage, 1 fatal. (-23) After lifting off from the chemical truck to begin spraying application, the witness on the truck stated that the aircraft was able to move forward but… ## Other investigations on N24HM (1) 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 CEN11CA403](https://openairdocs.org/ntsb/CEN11CA403), Jun 18, 2011: Bell 47G-4A (N24HM), Montgomery City, MO, substantial damage. Probable cause: A loss of control during the precautionary landing, which resulted in inadvertent contact between the main rotor and the tailboom. Contributing to the accident was the overloaded condition. ## Docket (4 files) The files NTSB released with the investigation on August 5, 2009, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=68659. 2.7 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 509 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40307253&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Master.PDF - Aircraft Logs (item 2, .PDF, 1.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40307254&FileExtension=.PDF&FileName=Aircraft%20Logs-Master.PDF - Service Bulletins & Letters (item 3, .PDF, 957 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40307256&FileExtension=.PDF&FileName=Service%20Bulletins%20%26%20Letters-Master.PDF - Toxicological Report (item 4, .PDF, 74 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40307258&FileExtension=.PDF&FileName=Toxicological%20Report-Master.PDF 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.