# NTSB ANC20LA053: Zenith Stol CH701, N324WS, Ambler, AK, May 31, 2020

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Class 3 · Limited · Final report
- Date: May 31, 2020, 12:33 local (20:33 UTC)
- Place: Ambler, AK
- Coordinates: 67.039443, -158.82943 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=67.0394&lon=-158.8294&mi=10
- Phase of flight: [Takeoff](https://openairdocs.org/ntsb-phases/300) (OpenAirDocs' grouping)
- Defining event: [Takeoff: Landing gear collapse](https://openairdocs.org/ntsb-events/094)
- Highest injury: No injuries
- Injuries: 2 uninjured
- Status: Completed
- Report: Approved by Office Director
- Investigation class: Class 3
- NTSB office: Alaska Regional Office
- Parties: Federal Aviation Administration
- NTSB case key (mKey): 101368
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ANC20LA053
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/101368/pdf
- NTSB docket: https://data.ntsb.gov/Docket?ProjectID=101368
- Page: https://openairdocs.org/ntsb/ANC20LA053

## Probable cause

The pilot’s improper decision to take off from unsuitable terrain, which resulted in impact with uneven terrain, the subsequent failure of the nosewheel fork, and a nose over.

## Findings

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

- [Landing gear system: nose/tail gear attach section](https://openairdocs.org/ntsb-findings/01023221): Aircraft › Aircraft systems · Capability exceeded (probable cause); cases with it: [Shrader David W CH-701, 1 case](https://openairdocs.org/ntsb-findings/01023221/cases.md?model=05632OF), [All aircraft, 29 cases](https://openairdocs.org/ntsb-findings/01023221/cases.md)
- [Terrain: rough terrain](https://openairdocs.org/ntsb-findings/03021015): Environmental issues › Physical environment · Contributed to outcome (probable cause); cases with it: [Shrader David W CH-701, 1 case](https://openairdocs.org/ntsb-findings/03021015/cases.md?model=05632OF), [All aircraft, 442 cases](https://openairdocs.org/ntsb-findings/03021015/cases.md)
- [Info processing/decision: decision making/judgment](https://openairdocs.org/ntsb-findings/02041520): Personnel issues › Action/decision · Pilot (probable cause); cases with it: [Shrader David W CH-701, 1 case](https://openairdocs.org/ntsb-findings/02041520/cases.md?model=05632OF), [All aircraft, 3,098 cases](https://openairdocs.org/ntsb-findings/02041520/cases.md)

## Sequence of events

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

- [Takeoff: Landing gear collapse](https://openairdocs.org/ntsb-events/094) (defining event); cases with it: [Shrader David W CH-701, 1 case](https://openairdocs.org/ntsb-events/094/sequence.md?model=05632OF), [All aircraft, 1,787 cases](https://openairdocs.org/ntsb-events/094/sequence.md)

## Analysis

The pilot, who was also the owner and builder of the experimental amateur-built airplane, reported that he landed the airplane on sand dunes. Forty-five minutes later, he took off from the sand dunes, and during the takeoff roll, the airplane hit some bumps. Just before the airplane reached rotation speed, it hit a larger bump, which propelled it upward. The airplane then descended in a nose-high attitude and impacted terrain, followed immediately by the nose landing gear (NLG) collapsing. Subsequently, the airplane nosed over and came to rest inverted. Postaccident examination of the airplane revealed that the rudder and both wing struts sustained substantial damage. The nosewheel fork had separated from the nose strut in three fragments at two fracture locations, one on each side of the nose strut attachment. Examination of the fracture surfaces revealed that all the fractures exhibited features consistent with overstress fracture in upward bending of the nosewheel fork. No evidence of preexisting cracks, wear marks, or corrosion was found. The pilot reported that the accident may have been prevented if he had conducted a more “detailed” inspection of the takeoff area. Given the evidence, it is likely that, during the takeoff roll, the NLG impacted uneven terrain, which led to the airplane becoming airborne in a nose-up attitude and then impacting terrain with force that exceeded the nosewheel fork’s structural capabilities and resulted in the nosewheel fracturing.

## Factual narrative

On May 31, 2020, about 1233 Alaska daylight time, an experimental amateur-built STOL CH-701 airplane, N324WS, was substantially damaged when it was involved in an accident at the Kobuk Sand Dunes near Ambler, Alaska. The sport pilot and passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot, who was also the owner and builder of the experimental amateur-built airplane, stated that he landed the airplane on sand dunes and then shut down for 45 minutes. He then took off, and the airplane hit “some bumps, but nothing significant,” until immediately before it reached the rotation speed of about 45 mph, at which point, the airplane hit a larger bump, which propelled it upward. The airplane then impacted terrain in a “nose high” attitude, followed immediately by the nose landing gear collapsing. Subsequently, the airplane nosed over and then came to rest inverted. The pilot reported that the accident might have been prevented if he had conducted a more “detailed inspection” of the takeoff area and “preflight inspection” of the nosewheel fork. Examination of the airplane revealed that the rudder and both wing struts sustained substantial damage. The part number 7L2-4J aluminum nosewheel fork had separated from the nose strut in three fragments at two fracture locations, one on each side of the strut attachment, at or near the four attachment bolt holes. The detailed examination revealed that the outer surfaces adjacent to the fractures exhibited outward lip-like deformation and the areas near the fractures on the inside (concave) of the fork exhibited secondary cracking perpendicular to the fractures. One of the fracture’s surface exhibited a dimpled rupture and dull and rough features. All the fracture features were consistent with overstress fracture in upward bending of the nosewheel fork. No evidence of preexisting cracks, wear marks, or corrosion was found. The chemical, electrical, and hardness characteristics of the middle fork fragment were consistent with an AA 6061 aluminum alloy in a T6 temper.

## Aircraft

- Registration: [N324WS](https://openairdocs.org/aircraft/N324WS), registered now, S/N 8836, built 2014 (OpenAirDocs)
- Reported make and model: ZENITH STOL CH701
- Registry model: [Shrader David W CH-701](https://openairdocs.org/model/shrader-david-w-ch-701) (registry code 05632OF) (OpenAirDocs)
- Registry engine: [Rotax 912UL](https://openairdocs.org/engine/rotax-912ul) (registry code 55592, reciprocating) (OpenAirDocs)
- Category: Airplane, amateur-built
- Serial number: 8836
- Year built: 2014
- Airframe hours: 289.2
- Engines: Rotax 912UL 80 horsepower reciprocating
- Damage: Substantial damage
- Flight: Personal, Part 91
- Airworthiness certificate: Special, Experimental (Special)
- Last inspection: Condition, May 18, 2020, 2 hours before
- Destination: PFNO, Noorvik, AK
- Equipment: Satellite tracking device, Electronic multifunction display, Angle of attack indicator, ADS-B, Stall warning system

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 54; injuries: none; sport pilot; airplane ratings: single-engine land; last flight review May 4, 2016; seat: left; restraint: lap only; flight hours: 347.3 total, 289.2 in this make and model

## Weather

- Conditions: Visual (VMC), Day
- Wind: 120° at 7 knots
- Visibility: 10 statute miles
- Lowest ceiling: none
- Temperature: 70 °F, dew point 37 °F
- Altimeter: 29.71 inHg
- Observed at: PAFM, 23 nm away

## 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 20200531008149A](https://openairdocs.org/incident/20200531008149A), May 31, 2020: Shrader David W CH-701, Ambler, AK, Substantial damage. Departed kotzebue AK. At 0800 flew east to kobuk sand dunes. Flight took 1.75 hours. Landed at dunes. PIC started departure roll at about 1230 to head back to…

## Docket (4 files)

The files NTSB released with the investigation on November 12, 2021, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=101368. 7.6 MB in all.

- Materials laboratory factual report (item 1, PDF, 9 pages, 11 photos, 2.7 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=10578742&FileExtension=pdf&FileName=20-041%20-%20Materials%20Lab%20Factual%20Report%20(ANC20LA053)-Rel.pdf
- Pilot/operator aircraft accident report, NTSB form 6120.1 (item 2, PDF, 10 pages, 4.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=9796345&FileExtension=pdf&FileName=6120%20master%202_Redacted-Rel.pdf
- Record of conversation pilot (shrader) (item 3, PDF, 2 pages, 317 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=9796069&FileExtension=pdf&FileName=ROC%20Shrader_Redacted-Rel.pdf
- Photographs (item 4, PDF, 2 pages, 451 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11575076&FileExtension=pdf&FileName=Photo%20Template%202-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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