# NTSB WPR11LA469: Bell 47D1, N9158R, Ahwahnee, CA, September 27, 2011 - Type: NTSB accident investigation - Classification: Accident · Serious injuries · Limited investigation · Final report - Date: September 27, 2011, 10:30 local (17:30 UTC) - Place: Ahwahnee, CA - Coordinates: 37.407501, -119.723335 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=37.4075&lon=-119.7233&mi=10 - Phase of flight: [Landing](https://openairdocs.org/ntsb-phases/550) (OpenAirDocs' grouping) - Defining event: [Landing: Loss of control in flight](https://openairdocs.org/ntsb-events/240) - Highest injury: Serious injuries - Injuries: 1 serious, 1 minor - Status: Completed, report June 28, 2012 - Report: Approved by Office Director - NTSB office: Western Pacific Region - Parties: Federal Aviation Administration - NTSB case key (mKey): 81906 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR11LA469 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/81906/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=81906 - Page: https://openairdocs.org/ntsb/WPR11LA469 ## Probable cause The pilot’s failure to maintain adequate main rotor rpm during the landing approach, which resulted in a loss of control. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Performance/control parameters: prop/rotor parameters](https://openairdocs.org/ntsb-findings/01062052): Aircraft › Aircraft oper/perf/capability · Not attained/maintained (probable cause); cases with it: [Bell 47D1, 1 case](https://openairdocs.org/ntsb-findings/01062052/cases.md?model=1180802), [All aircraft, 182 cases](https://openairdocs.org/ntsb-findings/01062052/cases.md) - [Use of equip/info: aircraft control](https://openairdocs.org/ntsb-findings/02063040): Personnel issues › Task performance · Pilot (probable cause); cases with it: [Bell 47D1, 3 cases](https://openairdocs.org/ntsb-findings/02063040/cases.md?model=1180802), [All aircraft, 9,295 cases](https://openairdocs.org/ntsb-findings/02063040/cases.md) - [Object/animal/substance: tree(s)](https://openairdocs.org/ntsb-findings/03022020): Environmental issues › Physical environment · Contributed to outcome; cases with it: [Bell 47D1, 1 case](https://openairdocs.org/ntsb-findings/03022020/cases.md?model=1180802), [All aircraft, 933 cases](https://openairdocs.org/ntsb-findings/03022020/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Landing: Loss of control in flight](https://openairdocs.org/ntsb-events/240) (defining event); cases with it: [Bell 47D1, 3 cases](https://openairdocs.org/ntsb-events/240/sequence.md?model=1180802), [All aircraft, 5,002 cases](https://openairdocs.org/ntsb-events/240/sequence.md) - [Landing: Collision with terr/obj (non-CFIT) ](https://openairdocs.org/ntsb-events/470); cases with it: [Bell 47D1, 3 cases](https://openairdocs.org/ntsb-events/470/sequence.md?model=1180802), [All aircraft, 10,189 cases](https://openairdocs.org/ntsb-events/470/sequence.md) ## Analysis The pilot and mechanic were on a local area flight to warm the oil before changing the oil lines. As they returned, the pilot slowed the helicopter and initiated a gradual descent to the landing site. The main rotor rpm decreased. As they continued the descent, the clearance from the trees surrounding the landing area was minimal. The pilot attempted to avoid the trees as he tried to regain main rotor rpm. The helicopter impacted a tree and descended nose down into the terrain. According to the mechanic and pilot, they encountered no mechanical anomalies during the flight. ## Factual narrative On September 27, 2011, at 1030 Pacific daylight time, a Bell 47D1, N9158R, collided with trees while descending near Ahwahnee, California. The helicopter was being operated under the provisions of Title 14 Code of Federal Regulations Part 91. The helicopter was substantially damaged. The private pilot sustained serious injuries, and the passenger sustained minor injuries. Visual meteorological conditions prevailed and no flight plan was filed. The pilot departed about 1020 for the local area flight. The Federal Aviation Administration (FAA) accident coordinator responded to the accident site. The helicopter had impacted terrain in a nose down attitude and the tail and tail rotor systems were resting upright against a tree. The pilot submitted a written statement on May 14, 2012. He reported that he was conducting a run on landing and the rotor revolutions per minute (RPM) decreased. He turned away from the trees hoping to recover the RPM. The helicopter then settled into a tree. He said that there were no mechanical malfunctions or failures. In an interview with the NTSB investigator, the passenger said that he had been maintaining the helicopter for about 5 years. The owner had reported what he surmised to be a problem with the number one bearing being loose on the tail rotor drive shaft. Additionally, they had previously installed an oil filter and they were going to change the oil lines. The pilot and mechanic completed the pre-flight inspection and review and noted no problems with the tail rotor drive shaft. They decided to take the helicopter on a short flight to warm the oil. The mechanic had flown with the pilot previously and had no concerns about his operation of the helicopter. They departed from the private landing pad which was located at the pilot's residence. They flew for about 15 minutes with no problems noted. They returned to the area of the landing pad which was surrounded by trees and terrain. The helicopter gradually descended and the mechanic told the pilot that he did not think they were going to maintain clearance from a large tree to the west of their position. About 10 yards from the tree, they were below treetop level and the power [rotor RPM] continued to decrease while the helicopter descended. The pilot attempted to pull out of the landing to avoid the tree and turned the helicopter to the right while increasing collective. The helicopter then collided with the tree. The mechanic had flown in and out of the area with the pilot multiple times. He felt on this occasion, due to the confined area there were no options to recover the helicopter prior to impact with the tree. The mechanic indicated that no mechanical malfunctions occurred. A witness was working as a fire lookout in Miami Mountain Fire Lookout Tower, which was located about 1 mile from the accident site. She heard the helicopter and saw a cloud of dust appear. The helicopter ascended out of the dust cloud and flew approximately 500 feet above ground leveldown a valley. The helicopter then turned and appeared to be returning to the landing pad. The landing pad was surrounded by trees and houses. As the helicopter approached the landing pad, it made a gradual descent while almost coming to a stop. She then saw the tail move from left to right, and the helicopter quickly descended and impacted a tree. The wind was calm at the time. There was no postimpact fire. She immediately called emergency response personnel. ## Aircraft - Registration: [N9158R](https://openairdocs.org/aircraft/N9158R), registered now, S/N 455, 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: 455 - Airframe hours: 4831 - Engines: FRANKLIN 6V4-178-B32 210 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Operator: Lee Haley - Registered owner: Lee Haley - Airworthiness certificate: Standard, Normal - Last inspection: Annual, June 14, 2011 - Departed: Ahwahnee, CA - Destination: Ahwahnee, CA ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 71; injuries: serious; private; medical: class 3, without waivers/limitations; seat: left ## Weather - Conditions: Visual (VMC), Day - Wind: calm - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 72 °F, dew point 52 °F - Altimeter: 30.04 inHg - Observed at: KMAE, 33 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 20110927022599A](https://openairdocs.org/incident/20110927022599A), Sep 27, 2011: Bell 47D1, Ahwahnee, CA, Substantial damage. On September 27, 2011, N9158R a Bell 47 helicopter, with the owner and a certificated mechanic on board conducting a maintenance flight were involved in an… ## Other investigations on N9158R (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 CHI84LA184](https://openairdocs.org/ntsb/CHI84LA184), May 20, 1984: Bell 47D1 (N9158R), Alpena, MI, destroyed ## Docket (5 files) The files NTSB released with the investigation on May 22, 2012, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=81906. 6.9 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 873 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40367937&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Redacted.PDF - FAA Record of Conversation (item 2, .PDF, 22 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40367737&FileExtension=.PDF&FileName=FAA%20Record%20of%20Conversation-Master.PDF - Passenger Record of Conversation (item 3, .PDF, 24 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40365469&FileExtension=.PDF&FileName=Passenger%20Record%20of%20Conversation-Master.PDF - Witness Record of Conversation (item 4, .PDF, 22 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40365470&FileExtension=.PDF&FileName=Witness%20Record%20of%20Conversation-Master.PDF - Photo 1. Helicopter at Accident Site (Provided by FAA) (item 5, .PDF, 6.0 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40367732&FileExtension=.PDF&FileName=Photo%201.%20Helicopter%20at%20Accident%20Site%20(Provided%20by%20FAA)-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.