# NTSB SEA04LA162: Universal Moulded Pdts. Monocoach, N11872, Pullman, WA, August 17, 2004 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: August 17, 2004, 09:30 local (16:30 UTC) - Place: Pullman, WA - Coordinates: 46.748611, -117.135559 - Nearby events: https://openairdocs.org/map.md?lat=46.7486&lon=-117.1356&mi=10 - Phase of flight: [Unknown](https://openairdocs.org/ntsb-phases/990) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 2 uninjured - Status: Completed, report January 24, 2005 - Report: Approved by Office Director - Parties: Spokane FSDO - NTSB case key (mKey): 59930 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=SEA04LA162 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/59930/pdf - Page: https://openairdocs.org/ntsb/SEA04LA162 ## Probable cause The failure of a landing gear oleo retaining nut safety clip (snap ring) at an unknown point in time, leading to the partial separation of the landing gear strut while in flight, and the full collapse of the strut during the subsequent landing. Factors include the grassy terrain that the pilot chose to execute the landing on. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, unknown - miscellaneous,dowel/pin - failure (cause) - landing gear,main gear shock absorbing strut - separation (cause) - Gear collapsed, landing - roll - landing gear,main gear strut - overload - terrain condition - grass (contributing factor) ## Analysis During a landing, just as the aircraft's two main wheels touched the surface of the runway, it suddenly jerked to the side and started to veer from the runway heading. The pilot therefore immediately added power and pulled the aircraft off the ground. He then climbed out to an altitude where he could visually inspect the gear legs and evaluate his situation. When he looked at the gear legs, he discovered that the left main gear strut oleo had come out of its housing, and the gear strut structure was hanging from the aircraft by two of its attach points. He therefore circled the area for awhile, waiting for emergency vehicles to get in place at the airport prior to his attempt to land on the remaining main gear. Once the equipment was in place, he landed on the grass alongside of the paved runway. The aircraft touched down on the right main gear, and the pilot kept the other gear leg elevated as long as possible. Eventually, as the aircraft slowed, the left gear strut dug into the terrain and collapsed. A post-accident inspection of the gear system determined that the landing gear shock strut retaining nut safety clip (snap ring) had failed, thus allowing the shock strut retaining nut to back off of its threads. Without this retaining nut in place, the oleo piston was free to drop out of its housing, leaving the landing gear only partially attached to the fuselage. ## Factual narrative On August 17, 2004, approximately 0930 Pacific daylight time, a Universal Moulded Products Monocoach, N11872, experienced a gear collapse during the landing roll at Pullman-Moscow Regional Airport, Pullman, Washington. The commercial 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 Porthill, Idaho, at 0745, was being operated in visual meteorological conditions. There was no report of an ELT activation. The aircraft was not on a flight plan. According to the pilot, just as the aircraft's two main wheels touched the surface of the runway, it suddenly jerked to the side and started to veer from the runway heading. He therefore immediately added power and pulled the aircraft off the ground. He then climbed out to an altitude where he could visually inspect the gear legs and evaluate his situation. When he looked at the gear legs, he discovered that the left main gear strut oleo had come out of its housing, and the gear strut structure was hanging from the aircraft by two of its attach points. He therefore circled the area for awhile, waiting for emergency vehicles to get in place at the airport prior to his attempt to land on the remaining main gear. Once the equipment was in place, he landed on the grass alongside of the paved runway. The aircraft touched down on the right main gear, and the pilot kept the other gear leg elevated as long as possible. Eventually, as the aircraft slowed, the left gear strut dug into the terrain and collapsed. A post-accident inspection of the gear system determined that the landing gear shock strut retaining nut safety clip (snap ring) had failed, thus allowing the shock strut retaining nut to back off of its threads. Without this retaining nut in place, the oleo piston was free to drop out of its housing, leaving the landing gear only partially attached to the fuselage. ## Aircraft - Registration: [N11872](https://openairdocs.org/aircraft/N11872), registered now, S/N 5012 (OpenAirDocs) - Reported make and model: Universal Moulded Pdts. Monocoach - Registry model: [Universal Moulded Products MONOCOACH](https://openairdocs.org/model/universal-moulded-products-monocoach) (registry code 9250102) (OpenAirDocs) - Registry engine: [Wright 760A B D E&ET](https://openairdocs.org/engine/wright-760a-b-d-e-et) (registry code 67009, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 5012 - Airframe hours: 1904 - Engines: Wright R760-8 235 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Operator: William C. Piper - Registered owner: Carsons Investments Inc. - Airworthiness certificate: Standard, Normal - Last inspection: Annual, May 1, 2004, 2 hours before - Departed: 1S1, Porthill, ID - Destination: PUW, Pullman, WA - Airport: PUW, Pullman-Moscow Reg., runway 23, 6,730 × 100 ft, grass/turf ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 74; injuries: none; commercial; airplane ratings: single-engine land, single-engine sea, multi-engine land; instrument ratings: airplane; medical: class 3, valid medical--w/ waivers/lim; last flight review August 11, 2004; seat: left; flight hours: 5,175 total, 10 in this make and model, 5,000 as pilot in command ## Weather - Conditions: Visual (VMC), Day - Wind: 270° at 5 knots - 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 20040817019379A](https://openairdocs.org/incident/20040817019379A), Aug 17, 2004: Unipro MONOCOACH, Pullman/Moscow, WA, Substantial damage. (-23) This aircraft landed at the Pullman, WA airport with the left hand landing gear dangling from the aircraft. The pilot stated that the landing was as slow… 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.