# NTSB CEN23LA350: Bell 206, N288AE, Carthage, IL, August 6, 2023

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Class 3 · Limited · Final report
- Date: August 6, 2023, 01:07 local (06:07 UTC)
- Place: Carthage, IL · Rural road near Carthage, IL.
- Coordinates: 40.370691, -91.052192 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=40.3707&lon=-91.0522&mi=10
- Phase of flight: [Landing](https://openairdocs.org/ntsb-phases/550) (OpenAirDocs' grouping)
- Defining event: [Landing: Collision during takeoff/land](https://openairdocs.org/ntsb-events/490)
- Highest injury: No injuries
- Injuries: 3 uninjured
- Status: Completed
- Report: Approved by Office Director
- Investigation class: Class 3
- NTSB office: Central Region
- Parties: Bell Flight, Transportation Safety Board of Canada, FAA Springfield FSDO, Air Evac Lifeteam
- NTSB case key (mKey): 192809
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN23LA350
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/192809/pdf
- NTSB docket: https://data.ntsb.gov/Docket?ProjectID=192809
- Page: https://openairdocs.org/ntsb/CEN23LA350

## Probable cause

A collision with a fence during landing due to the crew’s reduced distance estimation and depth perception while using night vision goggles. Contributing to the accident was the low moon angle, which made viewing the fence more challenging.

## Findings

NTSB's coded findings; those marked are part of the probable cause.

- [Attention/monitoring: monitoring environment](https://openairdocs.org/ntsb-findings/02021545): Personnel issues › Psychological · Pilot (probable cause); cases with it: [Bell 206L-3, 6 cases](https://openairdocs.org/ntsb-findings/02021545/cases.md?model=1182108), [All aircraft, 809 cases](https://openairdocs.org/ntsb-findings/02021545/cases.md)
- [Object/animal/substance: fence/fence post](https://openairdocs.org/ntsb-findings/03022047): Environmental issues › Physical environment · Awareness of condition (probable cause); cases with it: [Bell 206L-3, 1 case](https://openairdocs.org/ntsb-findings/03022047/cases.md?model=1182108), [All aircraft, 313 cases](https://openairdocs.org/ntsb-findings/03022047/cases.md)
- [Light condition: dark](https://openairdocs.org/ntsb-findings/03036020): Environmental issues › Conditions/weather/phenomena · Effect on operation (probable cause); cases with it: [Bell 206L-3, 2 cases](https://openairdocs.org/ntsb-findings/03036020/cases.md?model=1182108), [All aircraft, 448 cases](https://openairdocs.org/ntsb-findings/03036020/cases.md)
- [Object/animal/substance: fence/fence post](https://openairdocs.org/ntsb-findings/03022047): Environmental issues › Physical environment · Effect on equipment (probable cause); cases with it: [Bell 206L-3, 1 case](https://openairdocs.org/ntsb-findings/03022047/cases.md?model=1182108), [All aircraft, 313 cases](https://openairdocs.org/ntsb-findings/03022047/cases.md)
- [Info processing/decision: identification/recognition](https://openairdocs.org/ntsb-findings/02041510): Personnel issues › Action/decision · Pilot (probable cause); cases with it: [Bell 206L-3, 3 cases](https://openairdocs.org/ntsb-findings/02041510/cases.md?model=1182108), [All aircraft, 559 cases](https://openairdocs.org/ntsb-findings/02041510/cases.md)
- [Perception/orientation/illusion: perception](https://openairdocs.org/ntsb-findings/02022040): Personnel issues › Psychological · Pilot (probable cause); cases with it: [Bell 206L-3, 1 case](https://openairdocs.org/ntsb-findings/02022040/cases.md?model=1182108), [All aircraft, 61 cases](https://openairdocs.org/ntsb-findings/02022040/cases.md)
- [Object/animal/substance: fence/fence post](https://openairdocs.org/ntsb-findings/03022047): Environmental issues › Physical environment · Contributed to outcome (probable cause); cases with it: [Bell 206L-3, 1 case](https://openairdocs.org/ntsb-findings/03022047/cases.md?model=1182108), [All aircraft, 313 cases](https://openairdocs.org/ntsb-findings/03022047/cases.md)

## Sequence of events

The events NTSB coded, in order, by phase of flight. The defining event best describes what happened.

- [Landing: Off-field or emergency landing](https://openairdocs.org/ntsb-events/440); cases with it: [Bell 206L-3, 2 cases](https://openairdocs.org/ntsb-events/440/sequence.md?model=1182108), [All aircraft, 3,365 cases](https://openairdocs.org/ntsb-events/440/sequence.md)
- [Landing: Collision during takeoff/land](https://openairdocs.org/ntsb-events/490) (defining event); cases with it: [Bell 206L-3, 2 cases](https://openairdocs.org/ntsb-events/490/sequence.md?model=1182108), [All aircraft, 1,309 cases](https://openairdocs.org/ntsb-events/490/sequence.md)
- [Post-impact: Evacuation](https://openairdocs.org/ntsb-events/460); cases with it: [Bell 206L-3, 1 case](https://openairdocs.org/ntsb-events/460/sequence.md?model=1182108), [All aircraft, 103 cases](https://openairdocs.org/ntsb-events/460/sequence.md)

## Analysis

The air medical helicopter was dispatched to a remote area to pick up a patient in night visual meteorological conditions. While enroute, the aircrew received received a landing zone (LZ) brief that included information that a wire fence was located on the south side of the road. Upon approach to the LZ, the pilot and the flight nurse transitioned to and used night vision goggles (NVGs). The pilot performed both high and low reconnaissance and the aircrew verified that there were no poles or wires present. The flight nurse reported that she observed the fence on the south side of the road during this time; however, she thought the fence was farther away than it was. The pilot maneuvered the helicopter to a 10-ft hover over the road; the aircrew identified the wire fence on the south side of the road and noted that there were ditches on both sides of the road. The pilot initiated a right pedal turn and he planned to land so that the cabin door was oriented toward the accident scene. As the helicopter touched down, the pilot heard a “pop” noise and he felt feedback in the tail rotor pedals. The pilot realized the tail rotor system impacted the wire fence; he lowered the collective immediately and performed an emergency shutdown. The helicopter sustained substantial damage to the vertical stabilizer, the tail boom, the tail rotor driveshaft, and the two tail rotor blades. At the time of the accident, the moon was bright with 73% of its disk illuminated and it was at a relative angle of 25° above the horizon. According to NVG training references, terrain interpretation is generally more difficult when the moon is low on the horizon due to the lower light level and the shadows caused by the low angle. is the pilot likely had difficulty viewing the fence while using NVGs due to the lower light level and the presence of shadows. It is likely that, during the landing, the aircrew misjudged the distance of the wire fence due to the reduced distance estimation and depth perception while using NVGs.

## Factual narrative

On August 6, 2023, about 0107 central daylight time, a Bell 206 L-3 helicopter, N288AE, sustained substantial damage when it was involved in an accident near Carthage, Illinois. The pilot, the flight nurse, and the flight medic were not injured. The helicopter was operated as a Title 14 Code of Federal Regulations (CFR) Part 135 air ambulance flight. The crew (consisting of the pilot in the front right seat, the flight nurse in the rear left seat, and the flight medic in the rear right seat) were dispatched to pick up a patient from a remote area. The pilot completed the flight risk assessment just before the flight, with a low risk score, and accepted the flight. The operator’s operations control specialist also reviewed and acknowledged the completed flight risk assessment. The helicopter departed from the Southeast Iowa Regional Medical Center, Fort Madison, Iowa, at 0051. While enroute, the aircrew received an LZ brief that included information that the intended LZ was an east-to-west running dirt and gravel road with no wires; a wire fence was located on the south side of the road and corn fields were on the north and south sides of the road. Night visual meteorological conditions prevailed at the LZ and marking lights were placed on it. All of the helicopter’s external light sources were on for the approach and the landing. Upon approach to the LZ, the pilot and the flight nurse transitioned to and used NVGs. The flight medic was unaided and was not using NVGs. The pilot used the NVG-compatible searchlight to aid in scanning the LZ and the surrounding area for obstacles. The helicopter approached the LZ from the northwest and performed a high reconnaissance about 700 ft agl in a left orbit, confirming the LZ brief received from the fire department. The helicopter approached the LZ from north to south, perpendicular to the road. During the descent the aircrew performed a low reconnaissance, verified that there were no poles or wires present, and established visual contact with the fire department. The flight nurse reported that she observed the fence on the south side of the road during this time; however, she thought fence was farther away than it was. The pilot maneuvered the helicopter to a hover about 10 ft over the road; the aircrew identified the wire fence on the south side of the road and noted that there were ditches on both sides of the road. The pilot initiated a right-pedal turn and he planned to land so the cabin door was oriented toward the accident scene. This intended landing position would also provide visual contact with the fire department personnel entering and departing under the main rotor system and aid in patient loading. The heading of the helicopter was 310° when the pilot initiated the descent toward the road. As the helicopter touched down, the pilot heard a “pop” and felt feedback in the tail rotor pedals. The pilot realized the tail rotor system impacted the wire fence; he lowered the collective immediately andperformed an emergency shutdown. The helicopter came to rest upright on a heading of about 360°, perpendicular to the road and not the intended landing direction. The three aircrew members egressed the helicopter without further incident. The helicopter sustained substantial damage to the vertical stabilizer, tail boom, tail rotor driveshaft, and two tail rotor blades. At the time of the accident the moon was at a relative angle of 25° above the horizon and at an azimuth of 106°, with 73% of its disk illuminated. The moon had risen at 2311 on the previous day and set at 1155 on the accident day. The operator’s risk assessment program did not include information about moon altitude and brightness; however, this data is captured and analyzed on the operator’s daily crew briefing form. The operator reported there were no preimpact mechanical malfunctions or failures with the airframe or engine that would have precluded normal operation. The operator’s 14 CFR Part 135 NVG training program included information about moon angle, distance estimation, and depth perception. However, it did not include information about shadows, construction, terrain density, and vegetation. After the accident and at the suggestion of the NTSB investigator-in-charge, the operator updated their 14 CFR Part 135 NVG training program to include these additional areas regarding terrain interpretation. While not a required training reference for civilian aircrews, the U.S. Army has published Training Circular 3-04.4 Fundamentals of Flight, released in July 2022. This document discusses various topics used in the U.S. Army NVG training program. This document discusses distance estimation and depth perception and states in part: Distance estimation and depth perception are closely related. Distance estimation relates to determining distance to objects, while depth perception primarily refers to the relationship of objects to each other. The quality of both is affected by ambient light, type, and quality of NVG, degree of contrast in the field of view, and viewer's experience utilizing monocular cues. Objects tend to appear further away than they actually are. Reduction in visual acuity negatively influences distance estimation because we expect objects that are less distinct in detail to be farther than ones that possess sharp detail. This document further discusses moon angle when using NVGs and states in part: Moon angle has the same effect as the angle of the sun regarding ambient light levels. The position of the moon should be considered during each phase of aviation operations. However, the angle of the moon would have the most impact of LZ selection and landing direction. A low-angle moon may be beneficial in areas with little terrain relief. Terrain interpretation is generally more difficult when the moon is low on the horizon. This is due to the lower light level and the shadows caused by the low angle. However, when the moon is low on the horizon, terrain features orobjects on the skyline may be more recognizable. The Federal Aviation Administration does not provide reference material for NVG operations for the public regarding topics such as NVG operating characteristics, terrain interpretation, and operational considerations.

## Aircraft

- Registration: [N288AE](https://openairdocs.org/aircraft/N288AE), registered now, S/N 51327, built 1989 (OpenAirDocs)
- Reported make and model: BELL 206 (L3)
- Registry model: [Bell 206L-3](https://openairdocs.org/model/bell-206l-3) (registry code 1182108) (OpenAirDocs)
- Registry engine: [Allison 250-C30 series](https://openairdocs.org/engine/allison-250-c30-series) (registry code 03015, turbo-shaft) (OpenAirDocs)
- Category: Helicopter
- Serial number: 51327
- Year built: 1989
- Airframe hours: 17364.5
- Engines: Allison 250-C30 650 horsepower turbo shaft
- Damage: Substantial damage
- Flight: Other work use, Part 135
- Operator: Air Evac EMS, Inc., doing business as Air Evac Lifeteam
- Registered owner: Air Evac EMS, Inc.
- Airworthiness certificate: Standard, Normal
- Last inspection: AAIP, July 22, 2023, 22.9 hours before
- Departed: Fort Madison, IA
- Destination: Same as departure
- Flight plan: Company VFR
- Equipment: Electronic multifunction display, Electronic flight bag or handheld device, Auto-pilot, ADS-B, Satellite tracking device

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 54; injuries: none; commercial; airplane ratings: single-engine land; instrument ratings: helicopter; medical: class 2, with waivers/limitations; last flight review October 10, 2022; seat: right; restraint: 4-point; toxicology performed; flight hours: 4,142 total, 3,324 in this make and model, 3,925 as pilot in command, 66.5 in the last 90 days, 18.6 in the last 30 days, 3.3 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Night/bright
- Wind: calm
- Visibility: 8 statute miles
- Temperature: 66 °F, dew point 66 °F
- Altimeter: 29.93 inHg
- Observed at: KEOK, 18 nm away
- METAR: KEOK 060555Z AUTO 00000KT 8SM FEW045 FEW050 19/19 A2993 RMK A01

## 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 20230806008899A](https://openairdocs.org/incident/20230806008899A), Aug 6, 2023: Bell 206L-3, Carthage, IL, Substantial damage. The aircraft was facing north on e county rd 1200N approximately 5.25 miles from Carthage city center. The lat/long of the accident scene is: 40 degrees 22…

## Docket (15 files)

The files NTSB released with the investigation on June 5, 2024, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=192809. 15.4 MB in all.

- Pilot/operator aircraft accident report, NTSB form 6120.1 (item 1, PDF, 9 pages, 1.5 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16820264&FileExtension=pdf&FileName=NTSB%20Form%206120_1_Redacted-Rel.pdf
- Accident photographs (item 2, PDF, 11 pages, 2.7 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16827981&FileExtension=pdf&FileName=Accident%20Photographs-Rel.pdf
- Crew member statements - air evac lifeteam (item 3, PDF, 2 pages, 295 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16812078&FileExtension=pdf&FileName=Three%20Crew%20Member%20Statements_Redacted-Rel.pdf
- Accident flight ADS-B data (google earth .kmz file) (item 4, KMZ, 43 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16817070&FileExtension=kmz&FileName=20230806_A2EBB8_523616853-Rel.kmz
- Accident flight ADS-B data (microsoft excel .xlsx file) (item 5, XLSX, 1.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16816167&FileExtension=xlsx&FileName=20230806_A2EBB8_523616853_ADSB-Rel.xlsx
- Accident flight risk assessment - air evac lifeteam (item 6, PDF, 7 pages, 534 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16820204&FileExtension=pdf&FileName=Accident%20Flight%20Risk%20Assessment_Redacted-Rel.pdf
- Night vision goggle operations moon data - air evac lifeteam (item 7, PDF, 4 pages, 378 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16843451&FileExtension=pdf&FileName=NVG%20Operations%20Moon%20Data%20-%20Air%20Evac%20Lifeteam_Redacted-Rel.pdf
- Additional questions - air evac lifeteam (item 8, PDF, 6 pages, 1.0 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16818098&FileExtension=pdf&FileName=Air%20Evac%20EMS%20-%20Additional%20Questions_Redacted-Rel.pdf
- Crew member training records - air evac lifeteam (item 9, PDF, 19 pages, 4.7 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16820432&FileExtension=pdf&FileName=Air%20Evac%20Lifeteam%20-%20Crew%20Member%20Training%20Records_Redacted-Rel.pdf
- Additional questions - federal aviation administration (item 10, PDF, 2 pages, 77 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16830683&FileExtension=pdf&FileName=CEN23LA350%20FAA%20AVP-100%20MOR-Rel.pdf
- Meteorological information (item 11, PDF, 1 page, 86 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16811285&FileExtension=pdf&FileName=CEN23LA350%20Meteorological%20Information_Redacted-Rel.pdf
- U.S. Army training circular 3.04-4 fundamentals of flight (July 2022) - excerpts (item 12, PDF, 26 pages, 1.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16840217&FileExtension=pdf&FileName=U.S.%20Army%20Training%20Circular%203.04-4%20Fundamentals%20of%20Flight%20(July%202022)%20-%20Excerpts-Rel.pdf
- Safety improvements information - air evac lifeteam (item 13, PDF, 2 pages, 235 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16831413&FileExtension=pdf&FileName=Safety%20Improvements%20Information%20-%20Air%20Evac%20Lifeteam-Rel.pdf
- NTSB party member form - air evac lifeteam (item 14, PDF, 1 page, 808 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16811343&FileExtension=pdf&FileName=NTSB%20Party%20Member%20Form%20-%20Air%20Evac%20Lifeteam_Redacted-Rel.pdf
- Release of aircraft wreckage, NTSB form 6120.15 (item 15, PDF, 2 pages, 751 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16811901&FileExtension=pdf&FileName=NTSB%20Wreckage%20Release%20Form_Redacted-Rel.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.

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