# NTSB WPR12LA029: Bell 47D1, N4251A, San Diego, CA, November 8, 2011 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: November 8, 2011, 14:25 local (22:25 UTC) - Place: San Diego, CA - Coordinates: 32.572223, -116.980003 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=32.5722&lon=-116.9800&mi=10 - Phase of flight: [Emergency descent](https://openairdocs.org/ntsb-phases/600) (OpenAirDocs' grouping) - Defining event: [Autorotation: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) - Highest injury: No injuries - Injuries: 2 uninjured - Status: Completed, report August 29, 2012 - Report: Approved by Office Director - NTSB office: Western Pacific Region - Parties: Federal Aviation Adminstration FSDO - SAIBs cited in the narratives: [SAIB CE-09-35](https://openairdocs.org/saib/CE-09-35) (OpenAirDocs) - NTSB case key (mKey): 82270 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR12LA029 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/82270/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=82270 - Page: https://openairdocs.org/ntsb/WPR12LA029 ## Probable cause The flight instructor's inadequate supervision of the student pilot during a simulated autorotation and the pilots’ failure to use carburetor heat while operating at reduced engine power while in carburetor icing conditions, which resulted in a loss of engine power. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Action: delayed action](https://openairdocs.org/ntsb-findings/02041025): Personnel issues › Action/decision · Instructor/check pilot (probable cause); cases with it: [Bell 47D1, 1 case](https://openairdocs.org/ntsb-findings/02041025/cases.md?model=1180802), [All aircraft, 894 cases](https://openairdocs.org/ntsb-findings/02041025/cases.md) - [Ice/rain protection system: intake anti-ice, deice](https://openairdocs.org/ntsb-findings/01023020): Aircraft › Aircraft systems · Not used/operated (probable cause); cases with it: [Bell 47D1, 1 case](https://openairdocs.org/ntsb-findings/01023020/cases.md?model=1180802), [All aircraft, 108 cases](https://openairdocs.org/ntsb-findings/01023020/cases.md) - [Use of equip/info: use of equip/system](https://openairdocs.org/ntsb-findings/02063015): Personnel issues › Task performance · Pilot (probable cause); cases with it: [Bell 47D1, 2 cases](https://openairdocs.org/ntsb-findings/02063015/cases.md?model=1180802), [All aircraft, 1,391 cases](https://openairdocs.org/ntsb-findings/02063015/cases.md) - [Experience/qualifications: total experience](https://openairdocs.org/ntsb-findings/02031015): Personnel issues › Experience/knowledge · Instructor/check pilot; cases with it: [Bell 47D1, 1 case](https://openairdocs.org/ntsb-findings/02031015/cases.md?model=1180802), [All aircraft, 126 cases](https://openairdocs.org/ntsb-findings/02031015/cases.md) - [Temp/humidity/pressure: conducive to carburetor icing](https://openairdocs.org/ntsb-findings/03031030): Environmental issues › Conditions/weather/phenomena · Decision related to condition (probable cause); cases with it: [Bell 47D1, 1 case](https://openairdocs.org/ntsb-findings/03031030/cases.md?model=1180802), [All aircraft, 435 cases](https://openairdocs.org/ntsb-findings/03031030/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Autorotation: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) (defining event); cases with it: [Bell 47D1, 1 case](https://openairdocs.org/ntsb-events/341/sequence.md?model=1180802), [All aircraft, 3,820 cases](https://openairdocs.org/ntsb-events/341/sequence.md) - [Landing-flare/touchdown: Hard landing](https://openairdocs.org/ntsb-events/092); cases with it: [Bell 47D1, 5 cases](https://openairdocs.org/ntsb-events/092/sequence.md?model=1180802), [All aircraft, 2,102 cases](https://openairdocs.org/ntsb-events/092/sequence.md) ## Analysis During an instructional flight, a practice autorotation was initiated with the intention of performing a power recovery. The student maintained directional control while the certified flight instructor (CFI) adjusted the rotor rpm. The student initiated the power recovery, but the engine did not respond. The student then relinquished control of the helicopter to the CFI, who attempted to cushion the landing, but the helicopter landed hard. The helicopter's engine was equipped with a float-type carburetor, and the weather conditions provided for the possibility of serious carburetor icing at glide power. The accumulation of carburetor ice likely resulted in the loss of engine power. Neither the CFI nor student applied carburetor heat during the autorotation, nor they did not monitor the carburetor temperature gauge during the maneuver. During the postaccident examination of the engine, no mechanical failures or malfunctions were revealed which would have precluded normal operation. The CFI's flight experience in piston-powered helicopters was limited to the 6 hours of training he had provided in the accident helicopter, with his prior rotorcraft experience occurring exclusively in turbine-powered helicopters. This was also the first time he had performed an autorotation in the accident helicopter. ## Factual narrative On November 8, 2011, about 1425 Pacific standard time, a Bell 47D1 helicopter, N4251A, sustained substantial damage during a hard landing at Brown Field Municipal Airport, San Diego, California. The helicopter was being operated as a visual flight rules (VFR) instructional flight under the provisions of 14 Code of Federal Regulations (CFR) Part 91, when the accident occurred. The certified flight instructor (CFI) and the private pilot student/owner were not injured. The flight originated from Brown Field Municipal Airport, about 1355. Visual meteorological conditions prevailed, and no flight plan had been filed. The CFI reported that they had just performed a set of uneventful maneuvers in the traffic pattern, and decided to execute a practice autorotation from 1,000 feet above ground level (agl) to a power recovery at 200 feet agl. During the descent, the student maintained directional control, while the CFI adjusted the rotor rpm. The student then began to reapply engine power at 250 feet agl, however, the engine did not respond. He then relinquished the helicopter controls to the CFI, and the helicopter landed hard. The helicopter sustained substantial damage to the lower fuselage during the landing, and the main rotor blades struck and severed the tailboom. The helicopter was powered by a Franklin, six-cylinder, normally aspirated engine, and equipped with a float-type carburetor. The engine was examined by an inspector from the Federal Aviation Administration (FAA), and an Airframe and Powerplant Mechanic. The accessory case had become cracked during the impact sequence, and as such, the engine could not be operated. The fuel tank and carburetor bowl both contained fuel. A post impact examination did not reveal any anomalies with the engine that would have precluded normal operation. The carburetor icing probability chart from Federal Aviation Administration (FAA) Special Airworthiness Information Bulletin (SAIB): CE-09-35 Carburetor Icing Prevention, indicated a probability of serious icing at glide power at the temperature and dew point reported at the time of the accident. The CFI reported that he monitored the carburetor temperature gauge throughout the flight, and that its indicated temperature did not warrant the use of carburetor heat at any point leading up to the practice autorotation. Neither he nor the student applied carburetor heat during the autorotation, nor did they monitor the temperature during the maneuver. The CFI reported 510 flight hours providing flight training in rotorcraft. His total experience in the Bell 47 series was 6 hours, all of which was performed in the accident helicopter, with the owner present. CFI’s prior helicopter experience occurred exclusively in turbine-powered helicopters, and this was the first time he had performed an autorotation in a Bell 47. ## Aircraft - Registration: [N4251A](https://openairdocs.org/deregistered/N4251A-2013-08-09), registration cancelled 2013-08-09, S/N 110, built 1960 (OpenAirDocs) - Reported make and model: BELL 47D1 - Registry model: [Bell 47D1](https://openairdocs.org/model/bell-47d1) (registry code 1180802) (OpenAirDocs) - Registry engine: [Franklin 6V4 series](https://openairdocs.org/engine/franklin-6v4-series) (registry code 27033, reciprocating) (OpenAirDocs) - Category: Helicopter - Serial number: 110 - Airframe hours: 4727 - Engines: FRANKLIN 6V4 SERIES 210 horsepower reciprocating - Damage: Substantial damage - Flight: Instructional, Part 91 - Airworthiness certificate: Standard, Normal - Last inspection: Annual, October 3, 2011, 10 hours before - Departed: SDM, San Diego, CA - Destination: SDM, San Diego, CA - Airport: SDM, Brown Field, runway 26L, 3,180 × 75 ft, asphalt ## Flight crew As NTSB recorded them. NTSB leaves out names. - Flight instructor; age 47; injuries: none; military, commercial, flight instructor; airplane ratings: multi-engine land, single-engine land; instrument ratings: helicopter, airplane; medical: class 2, without waivers/limitations; last flight review September 23, 2011; seat: right; flight hours: 5,650 total, 6 in this make and model, 4,200 as pilot in command, 17 in the last 90 days, 14 in the last 30 days, 1 in the last 24 hours - Student pilot; age 36; injuries: none; private; airplane ratings: single-engine land; instrument ratings: airplane; medical: class 3, without waivers/limitations; last flight review November 14, 2010; seat: left; flight hours: 700 total, 6 in this make and model, 610 as pilot in command, 6 in the last 90 days, 6 in the last 30 days, 6 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 290° at 8 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 64 °F, dew point 37 °F - Altimeter: 30.14 inHg - Observed at: SDM ## 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 20111108026759A](https://openairdocs.org/incident/20111108026759A), Nov 8, 2011: Bell 47D1, San Diego, CA, Substantial damage. The owner of the aircraft was receiving rotorcraft flight instruction when the aircraft impacted the ground during an autorotation landing. The student stated… ## Other investigations on N4251A (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 CHI82DA196](https://openairdocs.org/ntsb/CHI82DA196), May 29, 1982: Bell 47D1 (N4251A), Le Sueur, MN, substantial damage ## Docket (7 files) The files NTSB released with the investigation on July 4, 2012, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=82270. 7.8 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 1.6 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40370986&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Redacted.PDF - CFI Statement Regarding Carburetor Heat and Prior Flight Experience (item 2, .PDF, 55 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40370987&FileExtension=.PDF&FileName=CFI%20Statement%20Regarding%20Carburetor%20Heat%20and%20Prior%20Flight%20Experience-Redacted.PDF - FAA Inspector Statement (item 3, .PDF, 218 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40371935&FileExtension=.PDF&FileName=FAA%20Inspector%20Statement-Redacted.PDF - Carburetor Icing Probablity Chart (item 4, .PDF, 63 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40371015&FileExtension=.PDF&FileName=Carburetor%20Icing%20Probablity%20Chart-Master.PDF - Photo 1 – Helicopter at Accident Site (item 5, .PDF, 1.9 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40370989&FileExtension=.PDF&FileName=Photo%201%20%E2%80%93%20Helicopter%20at%20Accident%20Site-Master.PDF - Photo 2 – Engine (item 6, .PDF, 2.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40370990&FileExtension=.PDF&FileName=Photo%202%20%E2%80%93%20Engine-Master.PDF - Photo 3 – Instrument Panel (item 7, .PDF, 1.8 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40370991&FileExtension=.PDF&FileName=Photo%203%20%E2%80%93%20Instrument%20Panel-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.