# NTSB ATL03LA106: Polstra Zodiac CH 601 HDS, N721PT, Thomson, GA, June 16, 2003 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: June 16, 2003, 09:27 local (13:27 UTC) - Place: Thomson, GA - Coordinates: 33.529724, -82.51667 - Nearby events: https://openairdocs.org/map.md?lat=33.5297&lon=-82.5167&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report September 1, 2004 - Report: Approved by Office Director - Parties: Atlanta FSDO - 11 - NTSB case key (mKey): 57253 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ATL03LA106 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/57253/pdf - Page: https://openairdocs.org/ntsb/ATL03LA106 ## Probable cause The total loss of engine power due to the fatigue fracture of the No. 3 cylinder intake valve, which resulted in a forced landing to rough terrain and subsequent collision with small trees and a tree stump. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Loss of engine power(total) - mech failure/malf, cruise - engine assembly,valve,intake - fractured (cause) - engine assembly,valve,intake - fatigue (cause) - Forced landing, emergency descent/landing - On ground/water encounter with terrain/water, emergency landing - terrain condition - rough/uneven (cause) - On ground/water collision with object, emergency landing - object - other - object - tree(s) ## Analysis During cruise flight, the engine began to run rough and lose power, then it stopped completely. The pilot executed an emergency landing in a field, and the airplane collided with small trees and a tree stump. Examination of the engine revealed the intake valve on the No. 3 cylinder was fractured in the transition region between the stem and the head with no bending deformation. Metallurgical examination revealed the lock for the spring seat displayed fretting damage at the internal and external faces. Fretting damage was observed on the corresponding surface of the stem portion of the valve and on the corresponding bore face of the spring seat. The fretting damage was characteristic of higher than normal operating stresses or vibration and fatigue. ## Factual narrative On June 16, 2003, at 0927 eastern daylight time, a Polstra Zodiac CH 601 HDS experimental airplane, N721PT, registered to and operated by the commercial pilot, collided with small trees and a tree stump during a forced landing in a field following a loss of engine power in Thomson, Georgia. The personal flight was operated under the provisions of Title 14 CFR Part 91 with no flight plan filed. Visual meteorological conditions prevailed. The commercial pilot was not injured, and the airplane sustained substantial damage. The flight departed Cobb County McCollum Field in Marietta, Georgia, at 0815 on June 16, 2003. The flight was en route to Thomson McDuffie County Airport, Thomson, Georgia. During cruise flight at 3,500 feet mean sea level approximately nine miles west of the airport, the engine began to run rough and lose power. The pilot stated the engine first made a tapping noise, followed by a louder noise. Attempts to restore engine power were unsuccessful. Approximately 6 miles from the airport, the propeller stopped completely and did not move during the pilot's attempts to restart the engine. The pilot executed an emergency landing in a field, and the airplane collided with small trees and a tree stump. Examination of the airplane revealed the nose gear was bent aft, the left main landing gear was bent, and the forward fuselage and wings were damaged. The propeller could not be turned by hand. Examination of the engine revealed the intake valve on the No. 3 cylinder was fractured in the transition region between the stem and the head. The pilot reported the engine was a Stratus EA-81 manufactured in 1997, and the total time on the engine was 83 hours since overhaul and 1.3 hours since inspection. The National Transportation Safety Board, Office of Research and Engineering, Materials Laboratory Division, performed metallurgical examination of the fractured valve head and stem portions, the spring seat, and half of the spring seat lock that were retrieved from the engine. Microscope examination of the mating fracture surfaces of the valve stem and head revealed the fine line features of the fracture were obliterated by mechanical damage. The valve stem portion displayed no bending deformation. The lock for the spring seat displayed fretting damage at the internal and external faces. Similar fretting damage was observed on the corresponding surface of the stem portion of the valve and on the corresponding bore face of the spring seat. The fretting damage was characteristic of higher than normal operating stresses or vibration and fatigue. ## Aircraft - Registration: [N721PT](https://openairdocs.org/deregistered/N721PT-2005-11-29), registration cancelled 2005-11-29, S/N 63423, built 2002 (OpenAirDocs) - Reported make and model: Polstra Zodiac CH 601 HDS - Registry model: [Polstra Philip ZODIAC CH 601 HDS](https://openairdocs.org/model/polstra-philip-zodiac-ch-601-hds) (registry code 0560300) (OpenAirDocs) - Registry engine: [Amateur-built UNKNOWN ENG](https://openairdocs.org/engine/amateur-built-unknown-eng) (registry code 99999) (OpenAirDocs) - Category: Airplane, amateur-built - Serial number: 63423 - Airframe hours: 79.6 - Engines: Stratus EA-81 100 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Airworthiness certificate: Special, Experimental (Special) - Last inspection: Annual, June 6, 2003, 1.3 hours before - Departed: RYY, Marietta, GA - Destination: HQU, Thomson, GA - Airport: KHQU, Thomson McDuffie County ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 34; injuries: none; commercial; airplane ratings: single-engine land; instrument ratings: airplane; medical: class 2, valid medical--no waivers/lim.; last flight review December 26, 2001; seat: left; flight hours: 1,100 total, 80 in this make and model, 1,050 as pilot in command, 150 in the last 90 days, 50 in the last 30 days, 5 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: calm - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 79 °F, dew point 72 °F - Altimeter: 30.04 inHg - Observed at: KDNL, 30 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 20030616016879A](https://openairdocs.org/incident/20030616016879A), Jun 16, 2003: Amtr ZODIAC, Thomson, GA, Substantial damage. (-23) On June 16, 2003, at approximately 9:20 am EDT, a polstra Zodiac ch 601 hds experimental aircraft, N721PT, registered to and operated by the private… 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.