# NTSB WPR21LA324: Cessna 172, N4110L, Athol, ID, August 7, 2021 - Type: NTSB accident investigation - Classification: Accident · No injuries · Class 4 · Limited · Final report - Date: August 7, 2021, 10:30 local (17:30 UTC) - Place: Athol, ID · maneuvering at altitude - Coordinates: 47.97796, -116.79269 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=47.9780&lon=-116.7927&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Defining event: [Maneuvering: Aircraft structural failure](https://openairdocs.org/ntsb-events/337) - Highest injury: No injuries - Injuries: 2 uninjured - Status: Completed - Report: Approved by Office Director - Investigation class: Class 4 - Basic report with no Prelim publish - NTSB office: Western Pacific Region - Parties: FAA-FSDO - NTSB case key (mKey): 103716 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR21LA324 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/103716/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=103716 - Page: https://openairdocs.org/ntsb/WPR21LA324 ## Probable cause The failure of the windshield during spin recovery for reasons that were not determined. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Windows-windshield system: flight compartment windows](https://openairdocs.org/ntsb-findings/01035610): Aircraft › Aircraft structures · Failure (probable cause); cases with it: [Cessna 172G, 1 case](https://openairdocs.org/ntsb-findings/01035610/cases.md?model=2072420), [All aircraft, 42 cases](https://openairdocs.org/ntsb-findings/01035610/cases.md) - [Not determined](https://openairdocs.org/ntsb-findings/05000000): Not determined › Not determined · Unknown/Not determined (probable cause); cases with it: [Cessna 172G, 4 cases](https://openairdocs.org/ntsb-findings/05000000/cases.md?model=2072420), [All aircraft, 2,247 cases](https://openairdocs.org/ntsb-findings/05000000/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Maneuvering: Aircraft structural failure](https://openairdocs.org/ntsb-events/337) (defining event); cases with it: [Cessna 172G, 1 case](https://openairdocs.org/ntsb-events/337/sequence.md?model=2072420), [All aircraft, 290 cases](https://openairdocs.org/ntsb-events/337/sequence.md) ## Analysis The flight instructor reported that before demonstrating spin recovery to the student pilot, he confirmed that the weight and balance met the requirements for the utility category. The flight instructor stated that as the spin reached the fully developed state, he began to execute the recovery procedure by reducing power to idle, ailerons remained at neutral, opposite rudder control to stop the turn, and the elevator forward. During the recovery, he noted that the airspeed did not exceed 110 mph which was 12 mph below the design maneuvering speed of 122 mph. Subsequently, the windshield shattered during the recovery process. The flight instructor immediately landed the airplane at the airport that he was maneuvering over without further incident. An examination of the airplane revealed that about half of the windshield separated. The airplane fuselage, wings and empennage were not damaged. The reason for the windshield failure was not determined. ## Aircraft - Registration: [N4110L](https://openairdocs.org/aircraft/N4110L), registered now, S/N 17254179, built 1966 (OpenAirDocs) - Reported make and model: CESSNA 172 (G) - Registry model: [Cessna 172G](https://openairdocs.org/model/cessna-172g) (registry code 2072420) (OpenAirDocs) - Registry engine: [Continental 0-300 series](https://openairdocs.org/engine/continental-0-300-series) (registry code 17022, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 17254179 - Year built: 1966 - Airframe hours: 3154 - Engines: CONT MOTOR 0-300 SER 145 horsepower reciprocating - Damage: Substantial damage - Flight: Instructional, Part 91 - Airworthiness certificate: None - Last inspection: Annual, October 12, 2020, 74 hours before - Departed: COE, Coeur d'Alene, ID - Destination: Same as departure - Airport: ID22, Treeport - Equipment: Stall warning system, ADS-B ## Flight crew As NTSB recorded them. NTSB leaves out names. - Flight instructor; age 21; injuries: none; commercial, flight instructor; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 1, without waivers/limitations; last flight review November 11, 2019; seat: right; restraint: 3-point; flight hours: 1,480 total, 410 in this make and model, 1,389 as pilot in command, 269 in the last 90 days, 112 in the last 30 days, 5 in the last 24 hours - Pilot-rated passenger; age 20; injuries: none; private; airplane ratings: single-engine land; medical: class 2, without waivers/limitations; last flight review August 6, 2021; seat: left; restraint: 3-point; flight hours: 63 total, 61 in this make and model, 15 as pilot in command, 63 in the last 90 days, 39 in the last 30 days, 4 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 180° at 7 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 70 °F, dew point 54 °F - Altimeter: 20.06 inHg - Icing: Unknown - Turbulence: Unknown - Observed at: KCOE, 13 nm away - METAR: KCOE 071556Z AUTO 18007KT 10SM CLR 21/12 A2006 ## Other investigations on N4110L (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 DEN69F0230](https://openairdocs.org/ntsb/DEN69F0230), May 9, 1969: Cessna 172G (N4110L), Albuquerque, NM, substantial damage ## Docket (3 files) The files NTSB released with the investigation on February 10, 2022, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=103716. 1.7 MB in all. - FAA inspection notes (item 1, PDF, 2 pages, 372 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=12753479&FileExtension=pdf&FileName=N4110L%20C172%20Athol%20ID%20-%20Windshield%20out%20spin%20training_Redacted-Rel.pdf - Flight instructor statement (item 2, PDF, 1 page, 31 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=12753674&FileExtension=pdf&FileName=Jonathon%20Report-Rel.pdf - Photo array-courtesy of airplane owner (item 3, PDF, 4 pages, 1.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=12753585&FileExtension=pdf&FileName=Photo%20Array-Airplane%20Owner-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.