# NTSB WPR09LA144: MD Helicopter 369D, N501EF, Trona, CA, March 7, 2009 - Type: NTSB accident investigation - Classification: Accident · Minor injuries · Limited investigation · Final report - Date: March 7, 2009, 10:00 local (18:00 UTC) - Place: Trona, CA - Coordinates: 36.216667, -117.083885 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=36.2167&lon=-117.0839&mi=10 - Phase of flight: [Approach](https://openairdocs.org/ntsb-phases/500) (OpenAirDocs' grouping) - Defining event: [Approach-VFR pattern final: Loss of tail rotor effectiveness](https://openairdocs.org/ntsb-events/242) - Highest injury: Minor injuries - Injuries: 3 minor - Status: Completed, report April 22, 2010 - Report: Approved by Office Director - NTSB office: Western Pacific Region - Parties: Boeing Helicopters, Federal Aviation Administration FSDO, Rolls-Royce - NTSB case key (mKey): 73448 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR09LA144 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/73448/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=73448 - Page: https://openairdocs.org/ntsb/WPR09LA144 ## Probable cause The pilot's failure to maintain control while landing in a high density altitude environment due to a loss of tail rotor effectiveness. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Temp/humidity/pressure: high density altitude](https://openairdocs.org/ntsb-findings/03031020): Environmental issues › Conditions/weather/phenomena · Contributed to outcome; cases with it: [Hughes Helicopters HUGHES 369D, 1 case](https://openairdocs.org/ntsb-findings/03031020/cases.md?model=4470706), [All aircraft, 278 cases](https://openairdocs.org/ntsb-findings/03031020/cases.md) - [Performance/control parameters: prop/rotor parameters](https://openairdocs.org/ntsb-findings/01062052): Aircraft › Aircraft oper/perf/capability · Capability exceeded (probable cause); cases with it: [Hughes Helicopters HUGHES 369D, 1 case](https://openairdocs.org/ntsb-findings/01062052/cases.md?model=4470706), [All aircraft, 182 cases](https://openairdocs.org/ntsb-findings/01062052/cases.md) - [Performance/control parameters: directional control](https://openairdocs.org/ntsb-findings/01062020): Aircraft › Aircraft oper/perf/capability · Not attained/maintained (probable cause); cases with it: [Hughes Helicopters HUGHES 369D, 1 case](https://openairdocs.org/ntsb-findings/01062020/cases.md?model=4470706), [All aircraft, 3,958 cases](https://openairdocs.org/ntsb-findings/01062020/cases.md) - [Use of equip/info: aircraft control](https://openairdocs.org/ntsb-findings/02063040): Personnel issues › Task performance · Pilot (probable cause); cases with it: [Hughes Helicopters HUGHES 369D, 11 cases](https://openairdocs.org/ntsb-findings/02063040/cases.md?model=4470706), [All aircraft, 9,295 cases](https://openairdocs.org/ntsb-findings/02063040/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Approach-VFR pattern final: Loss of tail rotor effectiveness](https://openairdocs.org/ntsb-events/242) (defining event); cases with it: [Hughes Helicopters HUGHES 369D, 1 case](https://openairdocs.org/ntsb-events/242/sequence.md?model=4470706), [All aircraft, 100 cases](https://openairdocs.org/ntsb-events/242/sequence.md) - [Approach-VFR pattern final: Loss of control in flight](https://openairdocs.org/ntsb-events/240); cases with it: [Hughes Helicopters HUGHES 369D, 11 cases](https://openairdocs.org/ntsb-events/240/sequence.md?model=4470706), [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: [Hughes Helicopters HUGHES 369D, 26 cases](https://openairdocs.org/ntsb-events/470/sequence.md?model=4470706), [All aircraft, 10,189 cases](https://openairdocs.org/ntsb-events/470/sequence.md) - [Post-impact: Fire/smoke (post-impact)](https://openairdocs.org/ntsb-events/170); cases with it: [Hughes Helicopters HUGHES 369D, 1 case](https://openairdocs.org/ntsb-events/170/sequence.md?model=4470706), [All aircraft, 354 cases](https://openairdocs.org/ntsb-events/170/sequence.md) ## Analysis The helicopter pilot was flying passengers and equipment to a landing zone on a peak with an elevation of 9,993 feet. He made one high pass around the summit and assessed the wind as light and variable. He made a right circling approach and slowed from 60 knots to 40 knots. The airspeed suddenly decreased to 20 knots and the helicopter yawed 90 degrees to the right. He temporarily stabilized the situation, but then the helicopter went into a violent and uncontrollable right spin. It spun down vertically until it collided with terrain, rolled onto its right side, and slid about 75 yards before coming to a stop facing uphill. One of the passengers held a rotorcraft/helicopter pilot certificate. He indicated that on the first landing attempt the pilot appeared to be running out of left pedal. The second attempt was at a different angle to the landing zone, but once again the pilot seemed to run out of left pedal and the helicopter began to spin. The pilot could not recover during the attempt and the helicopter made three turns before colliding with the terrain. The Rotorcraft Flying Handbook refers to unanticipated yaw that does not subside on its own as a loss of tail rotor effectiveness. It notes that, if not corrected, this can lead to a loss of control. It may occur in all single-rotor helicopters at airspeeds less than 30 knots. A common cause is insufficient tail rotor thrust for a given power setting at higher altitudes, where tail rotor thrust and efficiency are reduced. Another potential cause is encountering a quartering tailwind from certain directions. ## Factual narrative The Rotorcraft Flying Handbook describes unanticipated yaw as an uncommanded yaw rate that does not subside on its own. It notes that, if not corrected, this can lead to a loss of control of the helicopter. This is referred to as a loss of tail rotor effectiveness. It indicates that this condition is not related to equipment or maintenance, and may occur in all single-rotor helicopters at airspeeds less than 30 knots. The tail rotor does not provide adequate thrust to maintain directional control. Common causes are certain wind directions during hover, or insufficient tail rotor thrust for a given power setting at higher altitudes, where tail rotor thrust and efficiency are reduced. On March 7, 2009, about 1000 Pacific standard time, a MD Helicopter 369D, N501EF, collided with terrain near Trona, California. Airwest Helicopters, Inc., was operating the helicopter under the provisions of 14 Code of Federal Regulations (CFR) Part 135. The airline transport pilot and two passengers sustained minor injuries; the helicopter sustained substantial damage to the airframe. The cross-country, on-demand, air taxi flight departed the Wildrose National Park's heliport near Inyokern, California, about 0945. The purpose of the flight was to transport maintenance personnel to a radio tower. Visual meteorological conditions (VFR) prevailed, and a company VFR flight plan had been filed. The pilot departed Redlands, California, and stopped to refuel at Inyokern. He departed Inyokern, and landed at the heliport to load equipment. He then flew 6 miles east to a radio facility on top of Rogers Peak, elevation 9,993 feet. He noted that the peak was at the intersection of two ridge lines; one ran north/south, and the other ran east/west. The north-to-east quadrant consisted of very steep terrain; the other quadrants formed a large ice bowl with grades varying from 15 to 30 degrees. The pilot made one high reconnoiter right-hand turn around the summit. He assessed the wind as light and variable. He continued the circling approach from north to south, east of the ridge line and about 100 feet higher. He slowed from 60 knots to 40 knots so that he could assess his available power during the landing. The pilot felt that the helicopter was performing adequately with the torque level in the top of the green operating range on the torque gage. The airspeed suddenly decreased to 20 knots, and the helicopter yawed 90 degrees to the right. He held the new heading, lowered the nose to gain airspeed, and held the same torque input as he attempted to go over the ridge in order to abort the landing. The situation appeared stable until the helicopter went into a violent and uncontrollable right spin. The pilot indicated that he felt no response to his control inputs. He did not want to land in the ice bowl, and proceeded over the east/west ridge. He was unable to get forward airspeed and stop the spin. The helicopter spun down vertically, and he pulled all remaining pitch to cushionthe impact. The helicopter was on a southwesterly heading, and the main rotor blades made first contact followed by the skids. It rolled onto its right side, and slid about 75 yards before coming to a stop facing uphill. The right front passenger exited through where the bubble had been, and helped the rear passenger out. The pilot turned off the battery and fuel. He exited with the fire extinguisher, and put out a fire in the tailpipe. One of the passengers held a rotorcraft/helicopter pilot certificate. He indicated that on the first landing attempt, the pilot appeared to be running out of left pedal. The second attempt was at a different angle to the landing zone, but once again the pilot seemed to run out of pedal, and the helicopter began to spin. The pilot couldn't recover this time, and it made three turns before colliding with the terrain. Post accident examination of the wreckage revealed no anomalies with the engine that would have precluded normal operation. Examination of the airframe revealed a fracture of a component of the tail rotor control rod. Metallurgical examination determined that the fracture was a result of ductile overload during impact. No anomalies were discovered that would have precluded normal operation. ## Aircraft - Registration: [N501EF](https://openairdocs.org/aircraft/N501EF), registered now, S/N 270091D, built 1977 (OpenAirDocs) - Reported make and model: MD HELICOPTER 369D - Registry model: [Hughes Helicopters HUGHES 369D](https://openairdocs.org/model/hughes-helicopters-hughes-369d) (registry code 4470706) (OpenAirDocs) - Registry engine: [Allison 250 SER 400HP](https://openairdocs.org/engine/allison-250-ser-400hp) (registry code 03013, turbo-shaft) (OpenAirDocs) - Category: Helicopter - Serial number: 270091D - Airframe hours: 6897 - Engines: Rolls Royce 250 C20 420 horsepower turbo shaft - Damage: Substantial damage - Fire: On-Ground - Flight: Part 135 - Operator: Airwest Helicopters, Inc. - Registered owner: Airwest Helicopters, Inc. - Airworthiness certificate: Standard, Normal - Last inspection: 100 hour, October 11, 2008 - Departed: Inyokern, CA - Destination: Rogers Peak, CA - Flight plan: Company VFR ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 60; injuries: minor; private, airline transport, commercial; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 1, without waivers/limitations; last flight review December 26, 2008; seat: right; flight hours: 7,868 total, 1,300 in this make and model, 6,881 as pilot in command, 7 in the last 90 days, 6 in the last 30 days, 0 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: variable at 3 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 54 °F, dew point 21 °F - Altimeter: 30.11 inHg - Observed at: KIND, 205 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 20090307003959A](https://openairdocs.org/incident/20090307003959A), Mar 7, 2009: Hughes 369D, Inyokern, CA, Substantial damage. (-23) On 03/07/09 at approximately 1845Z (1045PDT), the pilot of aircraft N501EF, a Hughes 369D, was attempting to perform a high altitude landing at rogers… ## Docket (6 files) The files NTSB released with the investigation on February 11, 2010, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=73448. 1.7 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 259 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40323593&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Redacted.PDF - Passenger Weights (item 2, .PDF, 12 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40323595&FileExtension=.PDF&FileName=Passenger%20Weights-Redacted.PDF - Record of Conversation - Passenger (item 3, .PDF, 36 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40323596&FileExtension=.PDF&FileName=Record%20of%20Conversation%20-%20Passenger-Master.PDF - Boeing Release to use Report (item 4, .PDF, 39 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40325406&FileExtension=.PDF&FileName=Boeing%20Release%20to%20use%20Report-Redacted.PDF - Boeing Materials Lab Exam (item 5, .PDF, 1.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40324023&FileExtension=.PDF&FileName=Boeing%20Materials%20Lab%20Exam-Master.PDF - Statement of Party Representatives to NTSB Investigation (item 6, .PDF, 177 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40324091&FileExtension=.PDF&FileName=Statement%20of%20Party%20Representatives%20to%20NTSB%20Investigation-Redacted.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.