# NTSB CEN19LA176: Kolb Kolb Twinstar TSP 1, N217JM, Hector, MN, June 13, 2019 - Type: NTSB accident investigation - Classification: Accident · No injuries · Class 3 · Limited · Final report - Date: June 13, 2019, 09:50 local (14:50 UTC) - Place: Hector, MN - Coordinates: 44.731474, -94.712573 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=44.7315&lon=-94.7126&mi=10 - Phase of flight: [Landing](https://openairdocs.org/ntsb-phases/550) (OpenAirDocs' grouping) - Defining event: [Landing: Hard landing](https://openairdocs.org/ntsb-events/092) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Central Region - Parties: Federal Aviation Administration, Kolb Aircraft Company - NTSB case key (mKey): 99669 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN19LA176 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/99669/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=99669 - Page: https://openairdocs.org/ntsb/CEN19LA176 ## Probable cause The pilot’s operation of the airplane outside of the center of gravity limits, which resulted in an adverse aerodynamic condition and subsequent hard landing. Contributing to the accident was the pilot’s incorrect calculations of the airplane’s CG limits. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Use of equip/info: aircraft control](https://openairdocs.org/ntsb-findings/02063040): Personnel issues › Task performance · Pilot (probable cause); cases with it: [Milner James E KOLB TWINSTAR TSP-1, 1 case](https://openairdocs.org/ntsb-findings/02063040/cases.md?model=05613SR), [All aircraft, 9,295 cases](https://openairdocs.org/ntsb-findings/02063040/cases.md) - [Aircraft capability: cG/weight distribution](https://openairdocs.org/ntsb-findings/01061040): Aircraft › Aircraft oper/perf/capability · Capability exceeded (probable cause); cases with it: [Milner James E KOLB TWINSTAR TSP-1, 1 case](https://openairdocs.org/ntsb-findings/01061040/cases.md?model=05613SR), [All aircraft, 66 cases](https://openairdocs.org/ntsb-findings/01061040/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Landing: Hard landing](https://openairdocs.org/ntsb-events/092) (defining event); cases with it: [Milner James E KOLB TWINSTAR TSP-1, 1 case](https://openairdocs.org/ntsb-events/092/sequence.md?model=05613SR), [All aircraft, 2,102 cases](https://openairdocs.org/ntsb-events/092/sequence.md) ## Analysis The pilot was conducting a maintenance test flight and had been in the air about 15 minutes when airplane began to oscillate up and down. He had difficulty maintaining control, so he made a rapid descent toward the airport. During the rapid descent the oscillation and shaking reduced, but as he decreased the descent rate, the airplane oscillated violently. The airplane landed hard on the grass runway. The airplane sustained substantial damage to the wings, fuselage, and empennage. After the accident, the pilot stated that he thought the tail boom had fractured inflight. A postaccident examination of the airframe revealed that the tubular empennage structure had fractured and was separated. An examination of the fractured section determined that the fractures were due to overstress as a result of the hard landing. A review of the pilot’s calculated weight and balance information revealed that the pilot had incorrectly calculated the weight and balance and that the airplane’s center of gravity (CG) was aft of manufacturer limitations. After the accident, the pilot reported that he was adjusting his CG while airborne, and he placed a bag of bird seed in the passenger seat to assist during the inflight test. The bag was aft of the datum per the manufacturers specifications and would have moved the CG further aft. This likely resulted in an adverse aerodynamic condition and an uncontrollable pitch oscillation. ## Factual narrative On June 13, 2019, about 0950 central daylight time, a Kolb Twinstar TSP-1 light sport airplane, N217JM, was substantially damaged when it was involved in an accident at Hector Municipal Airport (1D6), Hector, Minnesota. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 post maintenance test flight. After takeoff, the pilot climbed the airplane to 500 ft above ground level (agl) and had been in the air about 15 minutes when the airplane began to oscillate up and down. He had difficulty maintaining control, so he made a rapid descent toward the airport. During the rapid descent, the oscillation and shaking decreased, but as he reduced the descent rate, the airplane oscillated violently. The airplane landed hard on the grass runway. After the accident, the pilot stated that he thought the tail boom had fractured inflight and was the source of the oscillation. The responding Federal Aviation Administration (FAA) inspector reported that the pilot had recently completed maintenance on the airplane on June 2, 2019, and was conducting a maintenance test flight. The inspector reviewed a hand-drawn center of gravity (CG) diagram from the pilot. The CG envelope as calculated by the pilot was incorrect and the diagram contained several errors. The pilot told the FAA in an additional statement that he was adjusting his CG while airborne, and he placed a bag of bird seed in the passenger seat to assist during the inflight test. The bag was aft of the datum per the manufacturers specifications and would have moved the CG further aft. A postaccident examination of the airframe revealed that the tubular empennage structure had separated at the “H section.” The fractured section was retained for metallurgical examination to identify the mode of fracture. Both halves of the fracture surfaces on the aluminum tube were examined by the NTSB’s Materials Laboratory in Washington, DC. All fractographic features were consistent with cantilever-bending overstress-fracture due to the application of a monotonically increasing load until fracture. There were no marks on the fracture surface indicating recontact of the fracture surfaces. The inside surface of the aluminum tail boom tube, where it contacted the steel H-section via pop rivets, exhibited intergranular network cracks consistent with stress corrosion cracking. The examination determined that the location of the network cracks did not contribute to the overstress fracture of the tube section. ## Aircraft - Registration: [N217JM](https://openairdocs.org/deregistered/N217JM-2022-02-05), registration cancelled 2022-02-05, S/N A-2, built 1986 (OpenAirDocs) - Reported make and model: Kolb KOLB TWINSTAR TSP 1 (III) - Registry model: [Milner James E KOLB TWINSTAR TSP-1](https://openairdocs.org/model/milner-james-e-kolb-twinstar-tsp-1) (registry code 05613SR) (OpenAirDocs) - Registry engine: [Bombardier ROTAX (ALL)](https://openairdocs.org/engine/bombardier-rotax-all) (registry code 09050, reciprocating) (OpenAirDocs) - Category: Airplane, amateur-built - Serial number: A-2 - Year built: 1986 - Airframe hours: 113 - Engines: Rotax 503 DCDI reciprocating - Damage: Substantial damage - Flight: Flight test, Part 91 - Airworthiness certificate: Special, Experimental (Special) - Last inspection: Condition, June 2, 2019, 0 hours before - Departed: 1D6, Hector, MN - Airport: 1D6, Hector Muni, runway 05, 2,580 × 165 ft, grass/turf ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 76; injuries: none; commercial; airplane ratings: multi-engine land, single-engine sea, single-engine land; medical: class 3, with waivers/limitations; seat: left ## Weather - Conditions: Visual (VMC), Day - Wind: calm - Visibility: 10 statute miles ## 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 20190613006899A](https://openairdocs.org/incident/20190613006899A), Jun 13, 2019: Milner James E KOLB TWINSTAR TSP-1, Hector, MN, Destroyed. Pilot felt a flutter at or about 500 AGL proceeded to airport to land, as the pilot attempted to flare the aircraft stalled and fell approximately 20' causing… ## Docket (10 files) The files NTSB released with the investigation on October 29, 2021, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=99669. 10.9 MB in all. - Pilot/operator aircraft accident report, NTSB form 6120.1 (item 1, PDF, 9 pages, 1.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11714333&FileExtension=pdf&FileName=6120%20-%20N217JM_Redacted-Rel.pdf - FAA inspector's statement - center of gravity (item 2, PDF, 1 page, 196 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=12854206&FileExtension=pdf&FileName=-%20FAA%20Statement%20-%20aft%20cg_Redacted2-Rel.pdf - FAA center of gravity envelope calculation (item 3, PDF, 1 page, 35 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11714761&FileExtension=pdf&FileName=Weight%20and%20Balance%20Gary%20numbers-Rel.pdf - Kolb weight and balance information (item 4, PDF, 2 pages, 409 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=12855894&FileExtension=pdf&FileName=Pages%20from%201990%20Kolb%20Mark%20III%20drawing%20book-Rel.pdf - Correspondence - email to NTSB (item 5, PDF, 2 pages, 115 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11715066&FileExtension=pdf&FileName=Pilot%20email%20statement_Redacted-Rel.pdf - Correspondence - email to FAA (item 6, PDF, 3 pages, 219 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11714066&FileExtension=pdf&FileName=Pilot%20statement%20to%20FAA_Redacted-Rel.pdf - Video file - hard landing (item 7, MP4, 2.6 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11714658&FileExtension=mp4&FileName=Accident%20sequence%20video-Rel.mp4 - Materials laboratory factual report 19-041 (item 8, PDF, 5 pages, 4 photos, 1.0 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11716714&FileExtension=pdf&FileName=Materials%20Laboratory%20Factual%20Report%2019-041-Rel.pdf - Drawings (engineering sketches) (item 9, PDF, 2 pages, 3.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11714702&FileExtension=pdf&FileName=Airplane%20drawings-Rel.pdf - Photos (item 10, PDF, 4 pages, 4 photos, 1.7 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11716783&FileExtension=pdf&FileName=Photos-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.