# NTSB CHI03LA274: Boeing A-75, N806RB, La Crosse, WI, August 20, 2003 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: August 20, 2003, 10:15 local (15:15 UTC) - Place: La Crosse, WI - Coordinates: 43.878887, -91.254447 - Nearby events: https://openairdocs.org/map.md?lat=43.8789&lon=-91.2544&mi=10 - Phase of flight: [Approach](https://openairdocs.org/ntsb-phases/500) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report June 2, 2004 - Report: Approved by Office Director - Parties: FAA-Milwaukee FSDO - NTSB case key (mKey): 57753 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CHI03LA274 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/57753/pdf - Page: https://openairdocs.org/ntsb/CHI03LA274 ## Probable cause The total loss of engine power due to a fatigue fracture of the engine's crankshaft. A factor was the corn crop. ## 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, approach - vfr pattern - final approach - engine assembly,crankshaft - failure,total (cause) - engine assembly,crankshaft - fatigue (cause) - Forced landing, emergency descent/landing - On ground/water encounter with terrain/water, emergency landing - terrain condition - crop (contributing factor) - Nose over, landing - roll ## Analysis The airplane sustained substantial damage when it nosed over during a forced landing to a cornfield after a total loss of engine power. The pilot reported the engine "suddenly began vibrating." The engine seized and the propeller stopped turning 10 seconds after the vibration started. He executed a forced landing to a cornfield, and the airplane nosed over during landing roll. The inspection revealed that the crankshaft was fractured in two pieces, with the fracture between the crankshaft rod journal and the front main bearing. Fatigue stress crack progression was observed on approximately 50 percent of the fracture surface. The cracking appeared to originate in the forward radius of the master-rod bearing journal. The remainder of the fracture surface exhibited conditions typical of tensile overload. The reason for the initiation of the crack in the journal radius of the crankshaft was not identified. The engine manufacturer's recommended time between overhaul (TBO) for the R-985 engine is 1,600 hours. The operator imposed a 1,200 hour TBO on the engines used in its fleet of airplanes. ## Factual narrative On August 20, 2003, at 1015 central daylight time, a Boeing A-75, N806RB, operated by Schwan's Aerial Marketing, sustained substantial damage during a forced landing to a cornfield after a total loss of engine power while on final approach to the La Crosse Municipal Airport (LSE), La Crosse, Wisconsin. The airline transport pilot was not injured. The 14 CFR Part 91 flight departed the Lawrence J Timmerman Airport (MWC), Milwaukee, Wisconsin, at 0845, with LSE as the destination airport. Visual meteorological conditions prevailed. No flight plan was filed. The pilot reported he was about three miles from LSE when the engine "suddenly began vibrating." He reported the engine seized and the propeller stopped turning 10 seconds after the vibration started. He executed a forced landing to a cornfield, and the airplane nosed over during landing roll. The pilot exited the airplane without injury. The 450 horsepower Pratt and Whitney R-985 radial engine had 1,150 hours since the last overhaul. It was shipped to Covington Aircraft, Okmulgee, Oklahoma, for inspection and engine teardown. The inspection revealed that the crankshaft was fractured in two pieces, with the fracture between the crankshaft rod journal and the front main bearing. Fatigue stress crack progression was observed on approximately 50 percent of the fracture surface. The cracking appeared to originate in the forward radius of the master-rod bearing journal. The remainder of the fracture surface exhibited conditions typical of tensile overload. The reason for the initiation of the crack in the journal radius of the crankshaft was not identified. (See Covington Aircraft, Radial Division, Engine Investigation Report #REIR9616) The maintenance manager for the aircraft operator reported that when the accident occurred, they had another airplane with an engine that had about 1,220 hours of operation since the last overhaul. That engine was also shipped to Covington Aircraft for teardown. The results of that inspection revealed that there was no damage to the crankshaft or other engine parts. The engine manufacturer's recommended time between overhaul (TBO) for the R-985 engine is 1,600 hours. The maintenance manager reported that the operator had voluntarily imposed a 1,400 hour TBO on the engines they operated when they first started using the R-985 in 1984. The maintenance manager reported that as a result of the crankshaft failure to N806RB, they imposed a TBO of 1,200 hours on the engines. He reported that the crankshaft failure was the only crankshaft failure in 90,000 - 95,000 hours of fleet operation. He also reported that the flight team pilots were restricted from performing snap rolls except during air shows and air show practice to reduce the stress placed on the crankshafts. ## Aircraft - Registration: [N806RB](https://openairdocs.org/aircraft/N806RB), registered now, S/N 75-4000, built 1942 (OpenAirDocs) - Reported make and model: Boeing A-75 - Registry model: [Boeing A75](https://openairdocs.org/model/boeing-a75) (registry code 1380108) (OpenAirDocs) - Registry engine: [Pratt & Whitney R-985 series](https://openairdocs.org/engine/pratt-whitney-r-985-series) (registry code 52008, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 75-4000 - Airframe hours: 11673 - Engines: Pratt & Whitney R-985 450 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Registered owner: Schwan's Aerial Marketing, LLC - Airworthiness certificate: Standard, Aerobatic - Last inspection: 100 hour, August 1, 2003, 20 hours before - Departed: MWC, MILWAUKEE, WI - Destination: LSE, La Crosse, WI - Airport: LSE, La Crosse Muni ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 64; injuries: none; flight instructor, commercial, airline transport; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 2, valid medical--w/ waivers/lim; last flight review December 31, 2002; seat: rear; flight hours: 17,526 total, 10,781 in this make and model, 16,931 as pilot in command, 168 in the last 90 days, 63 in the last 30 days, 4 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 210° at 12 knots - Visibility: 9 statute miles - Lowest ceiling: none - Temperature: 90 °F, dew point 73 °F - Altimeter: 29.89 inHg - Observed at: LSE, 3 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 20030820021559A](https://openairdocs.org/incident/20030820021559A), Aug 20, 2003: Boeing A75, Onalaska, WI, Substantial damage. (-23) On descent in lse airport engine began to shake hard, pilot retarded throttle and engine suddenly stopped. Landing initiated 3 miles north of lse airport… 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.