# NTSB DEN99LA015: Mooney M20C, N6405U, Englewood, CO, October 21, 1998 - Type: NTSB accident investigation - Classification: Accident · Serious injuries · Limited investigation · Final report - Date: October 21, 1998, 08:28 local (14:28 UTC) - Place: Englewood, CO - Coordinates: 39.579956, -104.859031 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=39.5800&lon=-104.8590&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: Serious injuries - Injuries: 1 serious - Status: Completed, report February 16, 2001 - Report: Approved by Office Director - NTSB case key (mKey): 45124 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=DEN99LA015 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/45124/pdf - Page: https://openairdocs.org/ntsb/DEN99LA015 ## Probable cause The undertorquing of the camshaft gear retaining bolts during engine overhaul by maintenance personnel. A factor was the unsuitable terrain for a forced landing. ## 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, climb - to cruise - engine assembly,camshaft - undertorqued (cause) - maintenance,overhaul - improper, other maintenance personnel (cause) - Forced landing, descent - emergency - In flight collision with terrain/water, emergency descent/landing - terrain condition - downhill - terrain condition - ground - terrain condition - none suitable (contributing factor) ## Analysis During climb following departure, the engine lost power. The pilot reported the emergency to the tower and attempted to return to the airport. Determining that he would be unable to make it back, he made an emergency landing in a field one and a half miles southeast of the airport. Postaccident examination of the engine revealed that the camshaft gear retaining bolts connecting the camshaft gear to the camshaft had lost torque. As a result, the lobes failed to open their respective valves, creating discontinuity to the gear train. The tread on each of the four camshaft gear bolts exhibited shiny, worn patterns. According to a Textron Lycoming engineer, loss of camshaft retaining bolt torque is indicative of the bolts being improperly torqued during the engine overhaul. According to aircraft maintenance records, the engine was overhauled on March 15, 1985, and had accumulated 833 hours since overhaul. ## Factual narrative On October 21, 1998, at 0828 mountain daylight time, a Mooney M20C, N6405U, owned and operated by the pilot, was substantially damaged when it collided with terrain following a loss of engine power during climb after departure from Centennial Airport, Englewood, Colorado. The private pilot, sole occupant aboard, sustained serious injuries. Visual meteorological conditions prevailed, and no flight plan was filed for the personal cross-country flight being conducted under Title 14 CFR Part 91. The intended destination was La Junta, Colorado. According to the pilot, takeoff from runway 10 was normal. While still in a climb, approximately five miles southeast of the airport, the engine lost power. He initiated emergency procedures for loss of engine power, but was unsuccessful in identifying the source of the failure. He reported the emergency to the tower and attempted to return to the airport. Determining that he would be unable to make it back, he made a forced landing in a field one and a half miles southeast of the approach end of runway 28. Postaccident examination of the engine revealed that the camshaft gear retaining bolts connecting the camshaft gear to the camshaft had lost torque. As a result, the lobes failed to open their respective valves, creating discontinuity to the gear train. Three of the retaining bolts, as well as locking tab fragments, were located in the oil sump. The one remaining bolt was fractured and appeared to have backed out before breaking. The tread on each of the four camshaft gear bolts exhibited shiny, worn patterns. The alignment pins had separated from the camshaft gear, and the gear holes were worn and elongated. In addition, the accessory housing revealed shiny wear marks, and the accessory breather shield was separated from the accessory case and found in fragmented pieces. According to the aircraft maintenance records, the engine was overhauled on March 15, 1985, at a tachometer time of 3,734.7 hours. The last annual inspection of the engine was performed on October 23, 1997, at a tachometer time of 4,455.2 hours. The engine had accumulated 833 hours since overhaul, and 112 hours since the last annual inspection. According to a Textron Lycoming engineer, loss of camshaft retaining bolt torque is indicative of the bolts being improperly torqued during the engine overhaul. The engineer stated that if the bolts are improperly torqued, they begin to vibrate and eventually wear, becoming disconnected, as was evident in this accident. If properly torqued, the bolts should have remained torqued until the next scheduled overhaul. ## Aircraft - Registration: [N6405U](https://openairdocs.org/deregistered/N6405U-2013-08-20), registration cancelled 2013-08-20, S/N 2152, built 1962 (OpenAirDocs) - Reported make and model: Mooney M20C - Registry model: [Thrush Robert L CAVALIER](https://openairdocs.org/model/thrush-robert-l-cavalier) (registry code 05622F4) (OpenAirDocs) - Registry engine: [Lycoming O&VO-360 series](https://openairdocs.org/engine/lycoming-o-vo-360-series) (registry code 41514, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 2152 - Airframe hours: 4567 - Engines: Lycoming O-360-A1D 180 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Registered owner: William D. Folkerts - Airworthiness certificate: Standard, Normal - Last inspection: Annual, October 23, 1997, 112 hours before - Departed: APA - Destination: LHX, LA JUNTA, CO - Airport: APA, Centennial Airport, runway 10, 4,903 × 62 ft, asphalt ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 45; private; airplane ratings: single-engine land; medical: class 3, valid medical--no waivers/lim.; seat: left; flight hours: 1,018 total, 834 in this make and model, 996 as pilot in command, 43 in the last 90 days, 2 in the last 30 days ## Weather - Conditions: Visual (VMC), Day - Wind: 180° at 7 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 43 °F, dew point 36 °F - Altimeter: 30.00 inHg - Observed at: APA ## 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 19981021044259A](https://openairdocs.org/incident/19981021044259A), Oct 21, 1998: Mooney M20C, Denver, CO, Substantial damage. (.4) During climb following departure, the engine lost power. The pilot reported the emergency to the tower and attempted to return to the airport. Determining… 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.