# NTSB FTW93LA216: Cessna 172N, N4884G, Purcell, OK, July 25, 1993 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: July 24, 1993, 22:20 local (Jul 25, 1993, 03:20 UTC) - Place: Purcell, OK - Coordinates: 35.010593, -97.370498 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=35.0106&lon=-97.3705&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 2 uninjured - Status: Completed, report September 26, 1994 - Report: Approved by Office Director - NTSB case key (mKey): 18796 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=FTW93LA216 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/18796/pdf - Page: https://openairdocs.org/ntsb/FTW93LA216 ## Probable cause THE LACK OF SUITABLE TERRAIN ONTO WHICH TO EXECUTE THE FORCED LANDING WHICH WAS NECCESITATED BY THE PARTIAL POWER LOSS. THE POWER LOSS WAS A RESULT OF THE FATIGUE FAILURE OF THE EXHAUST VALVE ROCKER ARM ATTACHMENT STUD. A FACTOR WAS THE NIGHT CONDITIONS. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Loss of engine power(partial) - mech failure/malf, cruise - normal - engine assembly,rocker arm/tappet - separation (cause) - engine assembly,rocker arm/tappet - fatigue (cause) - engine assembly,push rod - jammed - Forced landing, descent - emergency - light condition - bright night (contributing factor) - On ground/water encounter with terrain/water, landing - roll - terrain condition - none suitable (cause) ## Analysis THE AIRPLANE COLLIDED WITH ROUGH TERRAIN DURING A NIGHT FORCED LANDING FOLLOWING A PARTIAL POWER LOSS. THE ACCIDENT OCCURRED DURING A NIGHT DUAL INSTRUCTIONAL FLIGHT AND THE INSTRUCTOR MADE THE FORCED LANDING. INVESTIGATION REVEALED THAT THE #3 EXHAUST VALVE ROCKER ARM ATTACHMENT STUD HAD FAILED IN FATIGUE. THE SEPARATED STUD SUBSEQUENTLY LODGED UNDER THE #3 INTAKE VALVE MECHANISM AND THE CORRESPONDING PUSH ROD WAS BENT. THE ENGINE AND SUBJECT PARTS HAD ACCUMULATED A TOTAL OF 2,903.5 HOURS. ## Factual narrative On July 24, 1993, at approximately 2220 central daylight time, a Cessna 172N, N4884G, was substantially damaged when it collided with rough terrain during a forced landing near Purcell, Oklahoma. The forced landing was executed following a partial loss of engine power. The airplane was on a night cross country dual instructional flight. A VFR flight plan was filed and visual meteorological conditions prevailed throughout the area. Neither the instructor pilot nor the rated student pilot were injured. According to the instructor, the engine lost power down to 1,500 RPM while in cruise flight, about twenty minutes after takeoff from the Westheimer Airport in Norman, Oklahoma. The instructor stated that his efforts to regain power were unsuccessful and the airplane would not sustain level flight at the reduced power. He subsequently executed a forced landing to what appeared to be an open field. The airplane impacted rough terrain during the landing roll. The number 3 cylinder exhaust rocker arm attachment stud had separated at the face of the cylinder head. The separated stud was found lodged under the number 3 intake valve mechanism. The number 3 intake valve push rod was bent. The operator stated that the stud was examined by a metallurgy lab at the University of Oklahoma and the failure mechanism was determined to be fatigue. The engine and subject parts had accumulated a total of 2,903.5 hours. Neither the instructor nor the student submitted a pilot/operator accident report. Both subsequently left the country. ## Aircraft - Registration: [N4884G](https://openairdocs.org/deregistered/N4884G-2013-05-30), registration cancelled 2013-05-30, S/N 17273431, built 1979 (OpenAirDocs) - Reported make and model: CESSNA 172N - Registry model: [Cessna 172N](https://openairdocs.org/model/cessna-172n) (registry code 2072434) (OpenAirDocs) - Registry engine: [Lycoming 0-320 series](https://openairdocs.org/engine/lycoming-0-320-series) (registry code 41508, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 17273431 - Airframe hours: 2904 - Engines: LYCOMING O-320-H2AD 160 horsepower reciprocating - Damage: Substantial damage - Flight: Instructional, Part 91 - Registered owner: Airman'S Flight School, Inc. - Airworthiness certificate: Standard, Normal - Departed: OUN, NORMAN, OK - Destination: GLE, GAINESVILLE, TX - Flight plan: VFR ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 21; commercial; airplane ratings: single-engine land; instrument ratings: airplane; medical: class 1, valid medical--no waivers/lim.; seat: right; flight hours: 1,300 total, 200 in the last 90 days, 1 in the last 24 hours ## Weather - Conditions: Visual (VMC), Night/bright - Wind: 160° at 14 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 90 °F, dew point 64 °F - Altimeter: 29.00 inHg - Observed at: OKC, 20 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 19930724025399A](https://openairdocs.org/incident/19930724025399A), Jul 24, 1993: Cessna 172N, Purcell, OK, Substantial damage. Lost partial power on night dual. Landed rough field. NR3 rocker arm stud separated at cyl head from fatigue. 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.