# NTSB WPR10LA483: Boam Rans S-6S, N4427M, Roberts, ID, September 18, 2010 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: September 18, 2010, 09:10 local (15:10 UTC) - Place: Roberts, ID - Coordinates: 43.718612, -112.120552 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=43.7186&lon=-112.1206&mi=10 - Phase of flight: [Takeoff](https://openairdocs.org/ntsb-phases/300) (OpenAirDocs' grouping) - Defining event: [Takeoff: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report May 26, 2011 - Report: Approved by Office Director - NTSB office: Western Pacific Region - Parties: Federal Aviation Adminiatration FSDO - NTSB case key (mKey): 77521 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR10LA483 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/77521/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=77521 - Page: https://openairdocs.org/ntsb/WPR10LA483 ## Probable cause A loss of engine power due to the detachment of the left carburetor from the engine inlet manifold. Contributing to the accident was the pilot's failure to address a known engine vibration. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Engine fuel and control: fuel control/carburetor](https://openairdocs.org/ntsb-findings/01057322): Aircraft › Aircraft power plant · Inadequate inspection (probable cause); cases with it: [Boam Larry RANS S-6S, 1 case](https://openairdocs.org/ntsb-findings/01057322/cases.md?model=05619KJ), [All aircraft, 195 cases](https://openairdocs.org/ntsb-findings/01057322/cases.md) - [Engine fuel and control: fuel control/carburetor](https://openairdocs.org/ntsb-findings/01057322): Aircraft › Aircraft power plant · Damaged/degraded (probable cause); cases with it: [Boam Larry RANS S-6S, 1 case](https://openairdocs.org/ntsb-findings/01057322/cases.md?model=05619KJ), [All aircraft, 195 cases](https://openairdocs.org/ntsb-findings/01057322/cases.md) - [Inspection: scheduled/routine inspection](https://openairdocs.org/ntsb-findings/02061520): Personnel issues › Task performance · Pilot (probable cause); cases with it: [Boam Larry RANS S-6S, 1 case](https://openairdocs.org/ntsb-findings/02061520/cases.md?model=05619KJ), [All aircraft, 167 cases](https://openairdocs.org/ntsb-findings/02061520/cases.md) - [Maintenance: modification/alteration](https://openairdocs.org/ntsb-findings/02062030): Personnel issues › Task performance · Pilot (probable cause); cases with it: [Boam Larry RANS S-6S, 1 case](https://openairdocs.org/ntsb-findings/02062030/cases.md?model=05619KJ), [All aircraft, 69 cases](https://openairdocs.org/ntsb-findings/02062030/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Prior to flight: Aircraft inspection event](https://openairdocs.org/ntsb-events/050); cases with it: [Boam Larry RANS S-6S, 1 case](https://openairdocs.org/ntsb-events/050/sequence.md?model=05619KJ), [All aircraft, 229 cases](https://openairdocs.org/ntsb-events/050/sequence.md) - [Takeoff: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342) (defining event); cases with it: [Boam Larry RANS S-6S, 1 case](https://openairdocs.org/ntsb-events/342/sequence.md?model=05619KJ), [All aircraft, 1,858 cases](https://openairdocs.org/ntsb-events/342/sequence.md) - [Takeoff: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341); cases with it: [Boam Larry RANS S-6S, 1 case](https://openairdocs.org/ntsb-events/341/sequence.md?model=05619KJ), [All aircraft, 3,820 cases](https://openairdocs.org/ntsb-events/341/sequence.md) - [Landing-flare/touchdown: Collision with terr/obj (non-CFIT) ](https://openairdocs.org/ntsb-events/470); cases with it: [Boam Larry RANS S-6S, 1 case](https://openairdocs.org/ntsb-events/470/sequence.md?model=05619KJ), [All aircraft, 10,189 cases](https://openairdocs.org/ntsb-events/470/sequence.md) ## Analysis The pilot, who was also the airplane's owner, reported that the engine of the experimental amateur-built airplane experienced a partial loss of power while turning onto the crosswind leg of the traffic pattern after the initial takeoff climb. The pilot initiated a return to the runway, during which time the engine lost all power. The pilot unsuccessfully attempted to restart the engine and subsequently performed an off-airport landing. The airplane's right main landing gear collapsed during the landing roll, resulting in substantial damage to the airframe. Examination of the engine revealed that the left carburetor was detached from the engine inlet manifold. The impact trajectory, coupled with a lack of witness marks indicating the carburetor had struck any part of the airplane, make it most likely that the carburetor detached in flight. The owner/pilot reported that he had experienced excessive engine vibration and "kickback" during prior startups. He had considered a number of remedial measures to rectify the problem, but had not performed any of these measures prior to the accident flight. He additionally reported that he could have reduced the likelihood of the carburetor separating by more thoroughly examining the tension of its mounting hardware. ## Factual narrative HISTORY OF FLIGHT On September 18, 2010, about 0910 mountain daylight time, an experimental amateur-built Boam, Rans S-6S, N4427M, experienced a loss of engine power during takeoff from a private dirt airstrip near Roberts, Idaho. The pilot/owner was operating the airplane under the provisions of Title 14 Code of Federal Regulations Part 91. The commercial pilot was not injured, and the airplane sustained substantial damage. The local flight departed Roberts about 0910, with a planned destination of Rigby-Jefferson County Airport, Rigby, Idaho. Visual meteorological conditions prevailed, and no flight plan had been filed. The pilot reported that while turning crosswind after the initial takeoff climb, the engine experienced a partial loss of power. He initiated a return to the runway during which time the engine lost all power. He unsuccessfully attempted to restart the engine, and elected to perform an off-airport landing. During the descent he maneuvered around trees and obstacles, and was subsequently unable to level the airplane for the landing flare. The right main landing gear collapsed during the landing roll, resulting in substantial damage to the lower firewall and both wings. A deputy from the local sheriff's department responded to the accident site and reported that the fuel tank contained about 10 gallons of fuel. The airplane was subsequently recovered for examination. TESTS AND RESEARCH The high-wing, experimental amateur-built airplane was equipped with a Rotax 912 ULS engine, serial number 5643038. The engine was equipped with a two-blade composite propeller, and an overload clutch, also known as a 'slipper clutch'. Maintenance records indicated that the owner performed a conditional inspection on July 13, 2010, at an engine tachometer time of 428.8 hours. The owner reported a total engine time of 444.9 hours at the time of the accident. The airplane was initially examined by an inspector from the Federal Aviation Administration (FAA), and subsequently examined by a mechanic under the auspices of the NTSB investigator-in-charge. Examination revealed that the engine controls, linkages, cables, and hoses appeared intact and free of damage. No fluid leaks were noted, oil remained within the oil sump canister, and the engine rotated freely by hand via the propeller. Examination of the left carburetor revealed that it had become detached from the inlet manifold flange. The flange remained attached to the inlet manifold, with the carburetor clamp still in place over the rubber flange. The carburetor was observed about 1/2 inch below its nominal mounting position. The carburetor location was adjacent to the firewall; however, no damage to the firewall was noted that would indicate it made contact with the carburetor during the accident sequence. The engine was equipped with a carburetor support system, consisting of a support spring and bracket as specified in the Rotax Technical Bulletin 912-10. The bulletin stated in part that thesupport is used to reduce stress on the carburetor flange, incurred due to, 'Increased vibrations, unfavorable engine suspension, too heavy intake filter or intake silencer, erratic idling of engine and bad carburetor synchronization.' The airplane owner reported that on prior engine startups he had encountered excessive initial vibration and kickback, and as such, was considering the installation of a Soft Start Module (SSM). The SSM, according to its manufacturer, reduces engine kickback during startup by adjusting the initial ignition timing. The manufacturer further stated that engine kickback is often the result of slow cranking speed or an inadequately adjusted slipper clutch. The slow cranking speed can be caused by reduced electrical power available to the starter motor due to either a weak battery, or excessive battery cable length. The owner stated that he could have prevented the loss of power by more thoroughly inspecting the carburetor mounting clamp tension, installing an SSM, and by inspecting and adjusting the slipper clutch. ## Aircraft - Registration: [N4427M](https://openairdocs.org/aircraft/N4427M), registered now, S/N 08031518-S, built 2005 (OpenAirDocs) - Reported make and model: BOAM RANS S-6S - Registry model: [Boam Larry RANS S-6S](https://openairdocs.org/model/boam-larry-rans-s-6s) (registry code 05619KJ) (OpenAirDocs) - Registry engine: [Rotax SEE BOMBADIER](https://openairdocs.org/engine/rotax-see-bombadier) (registry code 55555, reciprocating) (OpenAirDocs) - Category: Airplane, amateur-built - Serial number: 08031518-S - Airframe hours: 429 - Engines: ROTAX 912ULS 100 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Airworthiness certificate: Special, Experimental (Special) - Last inspection: Condition, July 19, 2010, 16 hours before - Departed: PVT, Roberts, ID - Destination: U56, Rigby, ID - Airport: PVT, Tanner Airstrip, runway 20, 1,500 × 100 ft, grass/turf ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 78; injuries: none; commercial; airplane ratings: single-engine land, multi-engine land; instrument ratings: helicopter, airplane; medical: class 3, with waivers/limitations; last flight review July 16, 2009; seat: left; flight hours: 2,473 total, 445 in this make and model, 2,473 as pilot in command ## Weather - Conditions: Visual (VMC), Day - Wind: calm - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 54 °F, dew point 43 °F - Altimeter: 30.02 inHg - Observed at: IDE, 18 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 20100918046359A](https://openairdocs.org/incident/20100918046359A), Sep 18, 2010: Boam Larry RANS S-6S, Roberts, ID, Substantial damage. Pilt took off from a dirt airstrip near Roberts Idaho. When he was approximately 500 -600' AGL, the engine started running rough. He made a radio call to… ## Docket (7 files) The files NTSB released with the investigation on March 24, 2011, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=77521. 1.8 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 328 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40344796&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Redacted.PDF - FAA Inspector's Report (item 2, .PDF, 12 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40344797&FileExtension=.PDF&FileName=FAA%20Inspector%27s%20Report-Redacted.PDF - Mechanic's Report (item 3, .PDF, 69 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40344798&FileExtension=.PDF&FileName=Mechanic%27s%20Report-Redacted.PDF - Maintenance Logbook Excerpts (item 4, .PDF, 260 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40344799&FileExtension=.PDF&FileName=Maintenance%20Logbook%20Excerpts-Redacted.PDF - Soft Start Module Description, Retrieved from http://www.bullyhawk.com/ssm.htm, on March 6 2011 (item 5, .PDF, 51 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40344800&FileExtension=.PDF&FileName=Soft%20Start%20Module%20Description,%20Retrieved%20from%20http%3A%2F%2Fwww.bullyhawk.com%2Fssm.htm,%20on%20March%206%202011-Master.PDF - Photograph 1: Firewall Damage - FAA Photograph (item 6, .PDF, 480 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40344801&FileExtension=.PDF&FileName=Photograph%201%3A%20Firewall%20Damage%20-%20FAA%20Photograph-Master.PDF - Photograph 2: Left Carburetor - FAA Photograph (item 7, .PDF, 629 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40344802&FileExtension=.PDF&FileName=Photograph%202%3A%20Left%20Carburetor%20-%20FAA%20Photograph-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.