# NTSB SEA04LA117: Cessna 185F, N4585F, Bozeman, MT, June 24, 2004 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: June 24, 2004, 15:10 local (21:10 UTC) - Place: Bozeman, MT - Coordinates: 45.778057, -111.157501 - Nearby events: https://openairdocs.org/map.md?lat=45.7781&lon=-111.1575&mi=10 - Phase of flight: [Landing](https://openairdocs.org/ntsb-phases/550) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 2 uninjured - Status: Completed, report September 13, 2005 - Report: Approved by Office Director - Parties: Helena FSDO - NTSB case key (mKey): 59530 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=SEA04LA117 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/59530/pdf - Page: https://openairdocs.org/ntsb/SEA04LA117 ## Probable cause The failure of the right main gear brake disk attach flange during the landing roll, due to fatigue cracks emanating from numerous corrosion pits present on the surface of the disk, leading to the right brake becoming totally inoperative, and resulting in a rapid inadvertent ground-loop. Factors include hard braking applied by the pilot in order to turn off the active runway at an early taxiway, and considerable corrosion on the surface of the brake disk flange. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, landing - roll - landing gear,normal brake system - fractured (cause) - landing gear,normal brake system - inoperative (cause) - landing gear,normal brake system - corroded (contributing factor) - brakes(normal) - intentional, pilot in command - Loss of control - on ground/water, landing - roll - directional control - not possible, pilot in command (cause) - ground loop/swerve - inadvertent, pilot in command (cause) - On ground/water encounter with terrain/water, landing - roll - terrain condition - ground ## Analysis During the landing roll, the pilot was applying heavy braking in order to turn off the runway at taxiway Echo, when the aircraft suddenly and rapidly ground-looped to the left. An initial post-accident inspection of the aircraft revealed that the right main gear brake rotor assembly had torn lose from the wheel itself, rendering the right wheel brake totally inoperative. The wheel hub and brake disk assembly were shipped to the NTSB Materials Laboratory, where it was determined that the brake disk attachment flange failed in fatigue in the bend around the attachment flange. The brake disk showed a substantial amount of general corrosion, and although the attachment flange met the minimum thickness requirements, most of its surface was covered by corrosion and corrosion pitting. The fatigue crack propagation that eventually lead to the failure had originated in one of these corrosion pits. ## Factual narrative On June 24, 2004, approximately 1510 mountain daylight time, a Cessna 185F, N4585F, ground-looped during the landing roll at Gallatin Field, Bozeman, Montana. The private pilot and his passenger were not injured, but the aircraft, which is owned and operated by the pilot, sustained substantial damage. The 14 CFR Part 91 personal pleasure flight, which departed from an unknown location, was being operated in visual meteorological conditions. No flight plan had been filed. According to the pilot, during the landing roll he was applying normal heavy braking in order to turn off the runway at taxiway Echo, when the aircraft suddenly and rapidly ground-looped to the left. An initial post-accident inspection of the aircraft revealed that the right main gear brake rotor assembly had torn lose from the wheel itself, rendering the right wheel brake totally inoperative. The wheel hub and brake disk assembly were shipped to the NTSB Materials Laboratory, where it was determined that the brake disk attachment flange failed in fatigue in the bend around the attachment flange. The brake disk showed a substantial amount of general corrosion, and although the attachment flange met the minimum thickness requirements, most of its surface was covered by corrosion and corrosion pitting. The fatigue crack propagation that eventually lead to the failure had originated in one of these corrosion pits. The pilot did not return a completed NTSB Form 6120.1/2, so the total flight time information for this report was taken from data recorded on his last FAA medical examination. ## Aircraft - Registration: [N4585F](https://openairdocs.org/deregistered/N4585F-2019-09-06), registration cancelled 2019-09-06, S/N 1851092, built 1966 (OpenAirDocs) - Reported make and model: Cessna 185F - Registry model: [Cessna A185F](https://openairdocs.org/model/cessna-a185f) (registry code 2072821) (OpenAirDocs) - Registry engine: [Continental IO-520 series](https://openairdocs.org/engine/continental-io-520-series) (registry code 17032, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 1851092 - Engines: Continental IO-520-D 300 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Registered owner: Kenneth D. Chapman - Airworthiness certificate: Standard, Normal - Destination: BZN, Bozeman, MT - Airport: KBZN, Gallatin Field, runway 30, 9,003 × 150 ft, asphalt ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 58; injuries: none; private; airplane ratings: single-engine land; medical: class 3, with waivers/limitations; seat: left; flight hours: 2,450 total ## Weather - Conditions: Visual (VMC), Day - Visibility: 20 statute miles - Lowest ceiling: none - Temperature: 75 °F ## 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 20040624015999A](https://openairdocs.org/incident/20040624015999A), Jun 24, 2004: Cessna A185F, Bozeman, MT, Substantial damage. (-23) At approximately 1507 mountain daylight time, the pilot of N4585F landed on runway 30 at Bozeman/Gallatin field (bzn), in Bozeman, Montana. During his… ## Other investigations on N4585F (1) 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. - [NTSB WPR16FA131](https://openairdocs.org/ntsb/WPR16FA131), Jun 25, 2016: Cessna A185F (N4585F), Coeur d'Alene, ID, substantial damage, 1 fatal. Probable cause: The pilot's failure to maintain clearance from trees while maneuvering at low altitude in mountainous terrain. 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.