# NTSB CEN14LA401: Mosquito XE, Oshkosh, WI, August 1, 2014 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: August 1, 2014, 14:15 local (19:15 UTC) - Place: Oshkosh, WI - Coordinates: 44.024166, -88.561111 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=44.0242&lon=-88.5611&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Defining event: [Maneuvering: Part(s) separation from AC](https://openairdocs.org/ntsb-events/338) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report January 14, 2015 - Report: Approved by Office Director - NTSB office: Central Region - Parties: FAA - NTSB case key (mKey): 89784 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN14LA401 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/89784/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=89784 - Page: https://openairdocs.org/ntsb/CEN14LA401 ## Probable cause The failure of the retaining assembly on the tail rotor blade, which resulted in the separation of the blade and the subsequent loss of helicopter control. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Tail rotor: tail rotor blade](https://openairdocs.org/ntsb-findings/01046410): Aircraft › Aircraft propeller/rotor · Failure (probable cause); cases with it: [All aircraft, 31 cases](https://openairdocs.org/ntsb-findings/01046410/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Maneuvering: Part(s) separation from AC](https://openairdocs.org/ntsb-events/338) (defining event); cases with it: [All aircraft, 563 cases](https://openairdocs.org/ntsb-events/338/sequence.md) - [Uncontrolled descent: Collision with terr/obj (non-CFIT) ](https://openairdocs.org/ntsb-events/470); cases with it: [All aircraft, 10,189 cases](https://openairdocs.org/ntsb-events/470/sequence.md) ## Analysis Just after takeoff, the experimental, amateur-built helicopter started to rotate and then impacted the ground in a level attitude, which resulted in substantial damage to the helicopter. Examination revealed that one tail rotor blade had separated from the tail rotor and gearbox assembly and that the blade had separated cleanly from the assembly; neither the collar nor the pins used to secure the blade were located. The pilot reported that he had been testing this tail rotor design for 4 years. A tension/torsion strap and two steel pins were used to retain the blade. The strap was not completely restricted from movement, and, over time, movement and wear resulted in the failure of the retaining assembly. The tail rotor assembly was a unique design and was not used in any other application. ## Factual narrative On August 1, 2014, about 1415 central daylight time, a Mosquito XE amateur-built helicopter, Canadian-registered CF-HEZ was substantially damaged while maneuvering near Wittman Regional Airport (KOSH), Oshkosh, Wisconsin. The private pilot was not injured. Visual meteorological conditions prevailed for the flight. The helicopter was owned and operated by a private individual under the provisions of 14 Code of Federal Regulations Part 91 without a flight plan. The local flight departed approximately 1410. Just after takeoff, one tail rotor blade separated from the tail rotor and gearbox assembly. The helicopter started to rotate and impacted the ground in a level attitude, spreading both skids out horizontally. Both skids and the tail boom were substantially damaged. According to the Federal Aviation Administration inspector who examined the helicopter, the tail rotor blade had separated cleanly from the assembly. Neither the collar nor the pins used to secure the blade were located. The inspector reported that the tail rotor assembly was a unique design being tested and was not used in any other application. The pilot reported that he had been testing this tail rotor design for four years. He stated that a tension/torsion strap and two steel pins were used to retain the blade. The pilot stated that the strap was not completely restricted from movement and over time movement and wear resulted in the failure of the retaining assembly. The pilot reported that there were 82 hours on the tail rotor assembly and it had been 6 hours since it was last inspected. ## Aircraft - Registration: CF-HEZ (not matched to a registry record) - Reported make and model: MOSQUITO XE - Category: Helicopter, amateur-built - Serial number: 1004 - Year built: 2002 - Airframe hours: 251 - Engines: Inntec Inntec 800 85 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Airworthiness certificate: Special, Experimental (Special) - Last inspection: Condition, March 15, 2014 - Departed: OSH, Oshkosh, WI - Destination: OSH, Oshkosh, WI - Airport: KOSH, Wittman Regional Airport ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 50; injuries: none; private; airplane ratings: single-engine land; medical: class 3, without waivers/limitations; seat: single; restraint: lap only; flight hours: 399 total, 320 in this make and model ## Weather - Conditions: Visual (VMC), Day - Wind: variable at 3 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 81 °F, dew point 63 °F - Observed at: KOSH, 5 nm away ## Docket (2 files) The files NTSB released with the investigation on September 4, 2014, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=89784. 1.9 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 1.9 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40415989&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Redacted.PDF - Record of Conversation - FAA Inspector's Statement (item 2, .PDF, 67 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40415990&FileExtension=.PDF&FileName=Record%20of%20Conversation%20-%20FAA%20Inspector%27s%20Statement-Master.PDF 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.