# NTSB DEN00IA075: Beech A60, N457DA, Boulder, CO, November 9, 1999 - Type: NTSB incident investigation - Classification: Incident · No injuries · Incident investigation · Final report - Date: November 9, 1999, 11:00 local (18:00 UTC) - Place: Boulder, CO - Coordinates: 40.019439, -105.249847 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=40.0194&lon=-105.2498&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report April 6, 2001 - Report: Approved by Office Director - NTSB case key (mKey): 49020 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=DEN00IA075 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/49020/pdf - Page: https://openairdocs.org/ntsb/DEN00IA075 ## Probable cause The fatigue failure of the #6 cylinder connecting rod cap. ## 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, descent - normal - 1 engine - engine assembly,connecting rod cap - fatigue (cause) - engine assembly,connecting rod cap - failure,total (cause) ## Analysis The pilot said that as he descended to 6,500 feet mean sea level, the left engine of the twin-engine airplane failed. The pilot landed the airplane without further incident. The engine had 23.5 hours on it since major overhaul. An engine teardown revealed that the #6 connecting rod had failed. Examination of the #6 cylinder parts found preexisting fractures on both the rod cap and the connecting rod. The fatigue features displayed on the rod cap are suggestive of lower stress propagation than those stress propagation marks on the connecting rod. It appeared that the engine failure-initiating event was the failure of the rod cap. Examination of the #6 connecting rod bolts indicated that they fractured as a result of overstress. ## Factual narrative On November 9, 1999, approximately 1100 mountain standard time, a Beech A60, N457DA, received minor damage when the left engine failed during descent near Boulder, Colorado. The commercial pilot, the sole occupant in the airplane, was not injured. The airplane was being operated on a public use flight by the Boulder County Sheriff's Department under Title 14 CFR Part 91. Visual meteorological conditions prevailed for the cross-country flight that originated from Centennial Airport, Englewood, Colorado, approximately 20 minutes before the accident. The pilot had not filed a flight plan. The pilot said that as he descended to 6,500 feet mean sea level, the engine failed. The pilot landed the airplane without further incident. The engine had 23.5 hours on it since major overhaul. An engine teardown revealed that the #6 connecting rod had failed. Postaccident examination of the #6 cylinder parts, by the National Transportation Safety Board's (NTSB) Materials Laboratory, found preexisting fractures on both the rod cap and the connecting rod. The fatigue features displayed on the rod cap are suggestive of lower stress propagation than those stress propagation marks on the connecting rod. The NTSB's Materials Laboratory found that the two halves of the 2 separated rod bolts from the #6 cylinder (see attached report figures 7, 8, 9, and 10) exhibited surface separation features that were consistent with overstress separations. Additionally, the head portions of these two bolts both displayed bending deformation in an outward direction from the center of the connecting rod and rod cap. ## Aircraft - Registration: [N457DA](https://openairdocs.org/deregistered/N457DA-2022-07-02), registration cancelled 2022-07-02, S/N P-166 (OpenAirDocs) - Reported make and model: Beech A60 - Registry model: [Beech A60](https://openairdocs.org/model/beech-a60) (registry code 1153604) (OpenAirDocs) - Category: Airplane - Serial number: P-166 - Airframe hours: 6117 - Engines: Lycoming TIO-541E1C4 380 horsepower reciprocating - Damage: Minor damage - Flight: Public aircraft, Part 91 - Registered owner: Boulder County Sheriffs Dept - Airworthiness certificate: Standard, Normal - Last inspection: Annual, June 1, 1999 - Departed: APA, ENGLEWOOD, CO - Destination: 1V5 - Airport: 1V5, Boulder Municipal Airport, runway 26, 4,100 × 75 ft, asphalt ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 56; flight instructor, commercial; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 3, valid medical--w/ waivers/lim; seat: left; flight hours: 2,654 total, 1,036 in this make and model, 2,600 as pilot in command, 43 in the last 90 days, 23 in the last 30 days, 1 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 270° at 5 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 64 °F, dew point 30 °F - Altimeter: 29.00 inHg 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.