# NTSB ERA23LA284: Schweizer 269C, N9WZ, Macclenny, FL, July 1, 2023 - Type: NTSB accident investigation - Classification: Accident · Minor injuries · Class 3 · Limited · Final report - Date: July 1, 2023, 12:00 local (16:00 UTC) - Place: Macclenny, FL - Coordinates: 30.275833, -82.126667 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=30.2758&lon=-82.1267&mi=10 - Phase of flight: [Takeoff](https://openairdocs.org/ntsb-phases/300) (OpenAirDocs' grouping) - Defining event: [Takeoff: Ground resonance](https://openairdocs.org/ntsb-events/232) - Highest injury: Minor injuries - Injuries: 1 minor, 2 uninjured - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Eastern Region Aviation - Parties: Schweizer RSG, FAA/FSDO - NTSB case key (mKey): 192513 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ERA23LA284 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/192513/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=192513 - Page: https://openairdocs.org/ntsb/ERA23LA284 ## Probable cause The improper maintenance of the landing gear dampers and main rotor elastomeric dampers, resulting in ground resonance during an unsuccessful takeoff attempt with the helicopter near its maximum gross weight for the density altitude. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Landing gear system: main gear strut/axle/truck](https://openairdocs.org/ntsb-findings/01023213): Aircraft › Aircraft systems · Incorrect service/maintenance (probable cause); cases with it: [Schweizer 269C, 2 cases](https://openairdocs.org/ntsb-findings/01023213/cases.md?model=8059502), [All aircraft, 86 cases](https://openairdocs.org/ntsb-findings/01023213/cases.md) - [Temp/humidity/pressure: high density altitude](https://openairdocs.org/ntsb-findings/03031020): Environmental issues › Conditions/weather/phenomena · Contributed to outcome; cases with it: [Schweizer 269C, 3 cases](https://openairdocs.org/ntsb-findings/03031020/cases.md?model=8059502), [All aircraft, 278 cases](https://openairdocs.org/ntsb-findings/03031020/cases.md) - [Loading](https://openairdocs.org/ntsb-findings/01011500): Aircraft › Aircraft handling/service · Related operating info; cases with it: [Schweizer 269C, 1 case](https://openairdocs.org/ntsb-findings/01011500/cases.md?model=8059502), [All aircraft, 35 cases](https://openairdocs.org/ntsb-findings/01011500/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Takeoff: Ground resonance](https://openairdocs.org/ntsb-events/232) (defining event); cases with it: [Schweizer 269C, 6 cases](https://openairdocs.org/ntsb-events/232/sequence.md?model=8059502), [All aircraft, 21 cases](https://openairdocs.org/ntsb-events/232/sequence.md) ## Analysis According to the pilot, he flew the helicopter to the accident site earlier in the day with no anomalies noted during the preflight inspection, the flight itself, and the post-flight inspection. He said he briefed and loaded two passengers, which placed the helicopter near its maximum allowable gross weight and near its forward center-of-gravity (CG) limit. The pilot attempted the engine start but “inadvertently stalled the engine” during main rotor engagement. After the rotor stopped, he performed an engine start, rotor engagement, run-up, and a “ground check with no defects noted.” The pilot said when he started to raise the collective control for takeoff, he felt a “very slight vibration that subsided instantly” but he lowered the collective, performed a magneto check, checked the gauges, felt for any vibration, and listened for any malfunction. Everything seemed normal so he initiated the takeoff again. The pilot reported that as he began to raise the collective an “extremely violent” left-to-right rocking motion began. The pilot considered lifting the helicopter into the air in case the helicopter was in ground resonance, but he believed that the helicopter had experienced “a major malfunction and not ground resonance.” He lowered the collective, reduced the throttle to idle, and the helicopter, which had not left the ground, “disintegrated.” A witness recorded a 21-second video that showed the seconds before the accident and the accident itself. Sounds consistent with engine and main rotor operating rpm were heard before both rpm signatures appeared to droop as the helicopter became light on the skids and rotated nose-left around the main rotor mast about 20° before it settled to the ground. The helicopter then instantaneously rocked left and right, the main transmission and mast assembly became free of its mounts, and the turning main rotor destroyed the tailboom. A detailed examination of the wreckage and the maintenance records revealed damage consistent with a ground resonance event, and damage/degradation of main rotor elastomeric dampers and the landing gear dampers that predated the event. It is likely that the degraded condition of the dampers accelerated the helicopter's entry into ground resonance during the pilot's takeoff attempt. The records also revealed improper maintenance and missing entries for mandatory inspections. The sequence of events, the observed pattern of the helicopter’s self-destruction, and the damage signatures were all consistent with ground resonance. The loading of the helicopter near its maximum gross weight and the relatively high density altitude additionally compromised the control and power margins available to the pilot during the attempted takeoff. ## Factual narrative According to the FAA Helicopter Flying Handbook, Chapter 11, Helicopter Emergencies and Hazards: Helicopters with articulating rotors (usually designs with three or more main rotor blades) are subject to ground resonance, a destructive vibration phenomenon that occurs at certain rotor speeds when the helicopter is on the ground. Ground resonance is a mechanical design issue that results from the helicopter’s airframe having a natural frequency that can be intensified by an out-of-balance rotor. The unbalanced rotor disk vibrates at the same frequency (or multiple thereof) of the airframe’s resonant frequency, and the harmonic oscillation increases because the engine is adding power to the system, increasing the magnitude (amplitude) of the vibrations until the structure or structures fail. This condition can cause a helicopter to self-destruct in a matter of seconds. Hard contact with the ground on one corner (and usually with wheel-type landing gear) can send a shockwave to the main rotor head, resulting in the blades of a three-blade rotor disk moving from their normal 120° relationship to each other. This movement occurs along the drag hinge and could result in something like 122°, 122°, and 116° between blades. When another part of the landing gear strikes the surface, the unbalanced condition could be further aggravated. If the rpm is low, the only corrective action to stop ground resonance is to close the throttle immediately and fully lower the collective to place the blades in low pitch. If the rpm is in the normal operating range, fly the helicopter off the ground, and allow the blades to rephase themselves automatically. Then, make a normal touchdown. If a pilot lifts off and allows the helicopter to firmly re-contact the surface before the blades are realigned, a second shock could move the blades again and aggravate the already unbalanced condition. This could lead to a violent, uncontrollable oscillation. This situation does not occur in rigid or semi-rigid rotor disks because there is no drag hinge. In addition, skid-type landing gear is not as prone to ground resonance as wheel type landing gear, since the rubber tires' resonant frequency typically can match that of the spinning rotor, unlike the condition of a rigid landing gear. According to the helicopter’s Flight Training Manual: GROUND RESONANCE Ground resonance can develop when a series of ground shocks cause the rotor head to become unbalanced. This is usually caused by an uneven or rough landing in certain types of helicopters. This condition, if allowed to progress, can result in structural damage to the helicopter. Ground resonance can be recognized by progressively violent oscillations. There are two methods of recovery: 1. When flight rpm are present, immediately pull into a hover. 2. With low rpm, reduce collective and off throttle. The maximum allowable gross weight for the helicopter was 2,050 lbs. The maximum allowable cabin weight was 600 lbs. The estimated grossweight of the helicopter at the time of the accident was 1,931 lbs and within .8 inches of the helicopter’s forward CG limit. The calculations were based on an estimated half-tank of fuel, the known weights of the two adults, and the estimated weight of the minor child. Based on the 2,500-ft density altitude at the time of the accident, the manufacturer’s recommended takeoff weight was 1,890 lbs. Interpolation of performance charts in the Pilot’s Flight Manual revealed that at the estimated gross weight of 1,931 lbs, the helicopter should be capable of in-ground-effect hovering flight up to 3,700 ft density altitude. Examination of maintenance records revealed that the most recent annual and component inspections were performed referencing superseded and out-of-date maintenance manuals and checklists from the manufacturer. Additionally, the checklist was not applicable by serial number to the accident helicopter. An entry dated January 1, 2022, stated that an annual inspection was performed referencing “[type certificate data sheets] and manufacturer’s maintenance manuals,” yet none were referenced, and no check sheets were attached. Entries stated that both the front and rear landing gear dampers were “removed, inspected, recharged with nitrogen, and reinstalled”; however, neither customer service publications nor the helicopter manufacturer’s Handbook of Maintenance Instructions (HMI) contained any instruction for “recharging” the dampers. The helicopter’s main rotor elastomeric dampers were life-limited components that were subject to inspections every 600 hours of operation, yet no entries that documented a 600-hour extension check of the main rotor elastomeric dampers were provided. The life-limited component list attached to an entry dated February 7, 2023, revealed that the main rotor dampers were original to the helicopter and life-limited to 6,000 hours. On July 1, 2023, about 1200 eastern daylight time, a Schweizer 269C helicopter, N9WZ, was substantially damaged when it was involved in an accident near Macclenny, Florida. The commercial pilot sustained minor injuries, and two passengers were not injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 91 aerial observation flight. The pilot flew the helicopter to the accident site earlier in the day and reported no anomalies. He stated that before the accident flight he briefed and loaded two passengers, performed the engine start, and then “inadvertently stalled the engine” during main rotor engagement. After the rotor stopped, he performed an engine start, rotor engagement, run-up, and ground check with no defects noted. The pilot said that when he started to raise the collective control for takeoff, he felt a “very slight vibration that subsided instantly,” but he lowered the collective, performed a magneto check, checked the gauges, felt for any vibration, and listened for any malfunction. He stated that “everything seemed to be in order” and hesubsequently initiated the takeoff. The pilot reported that as he began to raise the collective an “extremely violent” left-to-right rocking motion began. The pilot considered lifting the helicopter into the air in case the helicopter was in ground resonance, but he believed that the helicopter had experienced “a major malfunction and not ground resonance.” He lowered the collective, reduced the throttle to idle, and the helicopter, which had not left the ground, “disintegrated.” A witness recorded a 21-second video that showed the seconds before the accident and the accident itself. The video was taken from behind the helicopter and was of low resolution. Sounds consistent with engine and main rotor operating rpm were heard before the engine and rotor noise decreased as the helicopter became light on the skids and rotated nose-left around the main rotor mast about 20° before it settled to the ground. The helicopter then instantaneously rocked left and right. The main transmission and mast assembly became free of its mounts and the turning main rotor destroyed the tailboom. The pilot, who was also the owner of the helicopter, held a commercial pilot certificate with ratings for airplane single-engine land, multi-engine land, instrument airplane, rotorcraft-helicopter, and instrument helicopter. His most recent FAA second-class medical certificate was issued September 1, 2022. The pilot reported 4,908 total hours of flight experience, of which 389 hours were in helicopters. According to the pilot, all his helicopter experience was in the accident helicopter. The helicopter was recovered to the pilot’s hangar. Examination of photographs revealed that the structure of the cockpit and the instrument panel were intact, but the overhead greenhouses and the pilot’s and copilot’s windscreens were fractured. The main transmission was free of its mounts and lay aft of the engine. The main rotor mast, with main rotor head attached, was secure in the transmission. All three blade hubs were secure in their grips. All three main rotor blades appeared to have been cut about 3 feet outboard of their respective grips during recovery operations. Remnants of the tailboom appeared entangled beneath the main rotor transmission and mast assembly. The helicopter was recovered and moved to a recovery facility in Jacksonville, Florida, where it was examined by an FAA aviation safety inspector. The postaccident examination revealed damage to the airframe, main rotor mast, and transmission consistent with a ground resonance event. All three main rotor elastomeric dampers displayed damage consistent with ground resonance. The displayed damage to the internal elastomer was consistent with damage that predated the accident impact/extension to the installed dampers. Hand-pressure testing of the main landing gear dampers revealed only the right rear oleo strut offered the expected resistance. Two of the remaining four dampers demonstrated less than the expected resistance, andone damper displayed zero resistance. According to the Pilot’s Flight Manual, 4-2, Pilot’s Preflight inspection: WARNING GROUND RESONANCE MAY RESULT IF HELICOPTER IS OPERATED WHEN THE LANDING GEAR DAMPERS ARE NOT IN GOOD CONDITION. IF EXTENSION IS NOT CORRECT, A DETAILED INSPECTION PROCEDURE MUST BE PERFORMED BEFORE FURTHER FLIGHT OPERATIONS. ## Aircraft - Registration: [N9WZ](https://openairdocs.org/aircraft/N9WZ), registered now, S/N S1882, built 2005 (OpenAirDocs) - Reported make and model: SCHWEIZER 269C - Registry model: [Schweizer 269C](https://openairdocs.org/model/schweizer-269c) (registry code 8059502) (OpenAirDocs) - Registry engine: [Lycoming HIO-360 series](https://openairdocs.org/engine/lycoming-hio-360-series) (registry code 41524, reciprocating) (OpenAirDocs) - Category: Helicopter - Serial number: S1882 - Year built: 2005 - Airframe hours: 2909.5 - Engines: Lycoming Engines HIO-360-D1A 190 horsepower reciprocating - Damage: Substantial damage - Flight: Aerial observation, Part 91 - Airworthiness certificate: Standard, Normal - Last inspection: Annual, February 7, 2023, 14 hours before - Destination: Same as departure - Airport: None - Equipment: Unknown ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 68; injuries: minor; flight instructor, commercial; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 2, with waivers/limitations; last flight review June 28, 2023; seat: left; restraint: 4-point; flight hours: 4,908.2 total, 389 in this make and model, 71.8 in the last 90 days, 23.5 in the last 30 days ## Weather - Conditions: Visual (VMC), Day - Visibility: 7 statute miles - Lowest ceiling: none - Temperature: 95 °F, dew point 72 °F - Altimeter: 30.03 inHg - Observed at: VQQ, 13 nm away - METAR: KVQQ 011550Z VRB04KT 7SM CLR 35/22 A3003= ## 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 20230701007619A](https://openairdocs.org/incident/20230701007619A), Jul 1, 2023: Schweizer 269C, Macclenny, FL, Substantial damage. Pilot stated they started the helicopter and thought they felt something then lowered the collective, performe a magneto check and checked gauges, felt for… ## Docket (10 files) The files NTSB released with the investigation on June 4, 2025, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=192513. 9.7 MB in all. - Pilot/operator aircraft accident report, NTSB form 6120.1 (item 1, PDF, 12 pages, 2.0 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=18466592&FileExtension=pdf&FileName=NTSB%20Form%206120_Redacted-Rel.pdf - Video file (item 2, MOV, 605 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=18449145&FileExtension=MOV&FileName=559EE80E-4B86-45E3-98D2-C95AE145DA1F-Rel.MOV - Pilot telephone interview memorandum for record (item 3, PDF, 1 page, 66 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=18439702&FileExtension=pdf&FileName=A%20-%20NTSB%20Memo%20of%20Record%20-%20Pilot%20(BR)-Rel.pdf - Memorandum for record - FAA inspector's wreckage and records examination (item 4, PDF, 4 pages, 238 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=18726786&FileExtension=pdf&FileName=A_Memorandum%20for%20Record%20Wreckage%20and%20Records%20Exam_Redacted-Rel.pdf - Annual inspections (item 5, PDF, 1 page, 2.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=18440066&FileExtension=pdf&FileName=Annual%20Inspection_Redacted-Rel.pdf - Life-limited components list (item 6, PDF, 1 page, 365 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=18734810&FileExtension=pdf&FileName=Life%20Limited%20Components%20List_Redacted-Rel.pdf - Ground resonance reference (Schweizer) (item 7, PDF, 1 page, 109 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=18440350&FileExtension=pdf&FileName=Hughes%20269A_Redacted-Rel.pdf - POH preflight warning and performance chart excerpts (item 8, PDF, 3 pages, 222 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=18448647&FileExtension=pdf&FileName=POH%20269C%20Preflight%20Warning%20and%20Performance%20Planning%20Excerpts-Rel.pdf - Release of aircraft wreckage, NTSB form 6120.15 (item 9, PDF, 1 page, 1.7 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=18440126&FileExtension=pdf&FileName=Release%20of%20Aircraft%20Wreckage%2023LA284_Redacted-Rel.pdf - Photo array (item 10, PDF, 4 pages, 1.9 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=18449314&FileExtension=pdf&FileName=ERA23LA284%20Photo%20Array-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. --- 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.