# NTSB CEN19LA240: Robinson R44, N7508Z, Blair, NE, July 27, 2019 - Type: NTSB accident investigation - Classification: Accident · Minor injuries · Class 3 · Limited · Final report - Date: July 27, 2019, 16:28 local (21:28 UTC) - Place: Blair, NE - Coordinates: 41.564167, -96.14083 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=41.5642&lon=-96.1408&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Defining event: [Maneuvering-low-alt flying: Sys/Comp malf/fail (non-power)](https://openairdocs.org/ntsb-events/330) - Highest injury: Minor injuries - Injuries: 1 minor - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Central Region - Parties: FAA, Robinson Helicopter Company - NTSB case key (mKey): 99945 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN19LA240 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/99945/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=99945 - Page: https://openairdocs.org/ntsb/CEN19LA240 ## Probable cause The failure of the lower actuator bearing support bracket, which resulted in the misalignment of the clutch actuator, the loss of belt tension on the main rotor drive system, and the subsequent forced landing on sloped terrain. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Main rotor drive: engine/transmission coupling](https://openairdocs.org/ntsb-findings/01046310): Aircraft › Aircraft propeller/rotor · Malfunction (probable cause); cases with it: [Robinson Helicopter R44 II, 2 cases](https://openairdocs.org/ntsb-findings/01046310/cases.md?model=7640122), [All aircraft, 24 cases](https://openairdocs.org/ntsb-findings/01046310/cases.md) - [Use of equip/info: aircraft control](https://openairdocs.org/ntsb-findings/02063040): Personnel issues › Task performance · Pilot (probable cause); cases with it: [Robinson Helicopter R44 II, 99 cases](https://openairdocs.org/ntsb-findings/02063040/cases.md?model=7640122), [All aircraft, 9,295 cases](https://openairdocs.org/ntsb-findings/02063040/cases.md) - [Terrain: sloped/uneven terrain](https://openairdocs.org/ntsb-findings/03021017): Environmental issues › Physical environment · Contributed to outcome (probable cause); cases with it: [Robinson Helicopter R44 II, 10 cases](https://openairdocs.org/ntsb-findings/03021017/cases.md?model=7640122), [All aircraft, 270 cases](https://openairdocs.org/ntsb-findings/03021017/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Maneuvering-low-alt flying: Sys/Comp malf/fail (non-power)](https://openairdocs.org/ntsb-events/330) (defining event); cases with it: [Robinson Helicopter R44 II, 9 cases](https://openairdocs.org/ntsb-events/330/sequence.md?model=7640122), [All aircraft, 994 cases](https://openairdocs.org/ntsb-events/330/sequence.md) - [Maneuvering-low-alt flying: Collision with terr/obj (non-CFIT) ](https://openairdocs.org/ntsb-events/470); cases with it: [Robinson Helicopter R44 II, 95 cases](https://openairdocs.org/ntsb-events/470/sequence.md?model=7640122), [All aircraft, 10,189 cases](https://openairdocs.org/ntsb-events/470/sequence.md) ## Analysis After completing a spray pass during a helicopter aerial application flight, the pilot initiated a climb over trees to head south. The pilot reported that, at the top of the climb, he noticed that the engine rpm was beyond "max limitations" and that the main rotor rpm was in the green range. The pilot initiated a right pedal turn to the north and decreased the engine throttle to lower the engine rpm. The engine rpm remained at the upper limit, but the main rotor rpm decreased. The pilot then attempted to correct the main rotor rpm by increasing the throttle; however, the main rotor rpm fluctuated and then continued to decrease. Unable to control and maintain the main rotor rpm, the pilot performed a forced landing to a field with sloped terrain, during which the main rotor blades impacted terrain. The helicopter sustained substantial damage to the main rotor blades and tailboom. Postaccident examination of the upper and lower actuator support bearing brackets revealed they were separated from the scroll, and evidence of fretting and rub marks was noted between the brackets and scroll walls. In addition, elongated rivet holes were observed on the scroll wall, and the associated rivets were sheared. Torque paint was noted on the outboard rivets. It is likely that the bracket supporting the lower actuator bearing became loose and sheared the rivets, which allowed the actuator bearing to shift and led to a subsequent misalignment of the clutch actuator. The misalignment of the clutch actuator resulted in the loss of belt tension between the engine and main rotor drive system. The reason for the loose bracket and sheared rivets could not be determined due to damage. A manufacturer service bulletin required an inspection of the brackets for evidence of fretting or looseness, and that was accomplished about 169 flight hours before the accident. The compliance procedure, which was to occur at the next 100-hour or annual inspection, was to visually inspect the brackets and attaching rivets for evidence of fretting or looseness and, on the lower bracket, to apply torque seal in a vertical stripe across both outboard rivets to lower scroll to facilitate future inspections. It is likely that the wear was not apparent at the time of the inspection. ## Factual narrative On July 27, 2019, at 1628 central daylight time, a Robinson R44 II helicopter, N7508Z, impacted terrain near Blair, Nebraska. The pilot sustained minor injuries, and the helicopter sustained substantial damage to the main rotor blades and tailboom. The helicopter was registered to and operated by NE IA Helicopters, LLC, Tekamah, Nebraska, as a Title 14 Code of Federal Regulations Part 137 aerial application flight. Day visual meteorological conditions prevailed at the time of the accident, and a flight plan was not filed. The local flight departed an off-airport location for aerial application operations. According to the pilot, after completing the last spray pass, he initiated a climb over a tree ridge and began to head towards the south. At the top of the climb, he noticed the engine RPM was beyond "max limitations," and the main rotor RPM was in the green range. The pilot initiated a right pedal turn to the north and decreased the engine throttle in an attempt to lower the engine RPM. After adjusting the engine throttle, the engine RPM remained at the upper limit, but the main rotor RPM decreased. The pilot then attempted to correct the main rotor RPM by increasing the throttle; however, the main rotor RPM fluctuated up and down, and continued to decrease. Unable to control and maintain the main rotor RPM, the pilot performed a forced landing to a corn field. During the forced landing to sloped terrain, the main rotor blades impacted the terrain, and the helicopter came to rest upright. A review of the aircraft records revealed Robinson Helicopter Company service bulletin (SB) 94, Subject: Actuator Lower Bearing A185 Brackets, issued June 8, 2017, was completed on May 5, 2018, at an aircraft total time of 2,181.3 hours. The compliance procedure was to visually inspect the A185 brackets and attaching rivets for evidence of fretting or looseness, and on the lower A185 bracket, apply torque seal in a vertical stripe across both outboard rivets to lower scroll to facilitate future inspections. The records also revealed the most recent 100-hour/annual inspection was completed on May 3, 2019, at a total airframe time of 2,244.0 hours. The total airframe time at the accident was 2,350.5 hours. A postaccident examination included the removal of the clutch assembly, freewheel clutch, belt tension actuator, time delay assembly, cooling fan, sections of the scroll, and actuator bearing support brackets. The components were shipped to Robinson Helicopter Company for further examination. The components were examined by a National Transportation Safety Board engineer and a technical representative of the Robinson Helicopter Company. The lower actuator support bearing bracket had separated from the scroll. Torque paint had been applied on the outer rivets, in accordance with SB-94. Fretting and rub marks were also noted between the bracket and scroll wall. Elongated rivet holes were observed on the scroll wall, and associated rivets were sheared. The upperactuator bearing support brackets were separated from the scroll and displayed fretting and rub marks between the brackets and scroll wall. All rivet holes were elongated and the rivets were sheared. The clutch actuator upper housing had fractured from housing to slider tube. The fracture surface was jagged and angular. The actuator screw was fractured at the worm gear interface in a thread grove, and the fracture surface was jagged and angular. As received, the cooling fan was tested and found to be out of balance per the manufacturer specifications; however, the fan is dynamically balanced once installed on the airframe which may be different as received from the manufacturer. ## Aircraft - Registration: [N7508Z](https://openairdocs.org/aircraft/N7508Z), registered now, S/N 10609, built 2005 (OpenAirDocs) - Reported make and model: Robinson R44 (II) - Registry model: [Robinson Helicopter R44 II](https://openairdocs.org/model/robinson-helicopter-r44-ii) (registry code 7640122) (OpenAirDocs) - Registry engine: [Lycoming IO-540-AE1A5](https://openairdocs.org/engine/lycoming-io-540-ae1a5) (registry code 41899, reciprocating) (OpenAirDocs) - Category: Helicopter - Serial number: 10609 - Year built: 2005 - Airframe hours: 2350.5 - Engines: Lycoming IO-540-AE1A5 reciprocating - Damage: Substantial damage - Flight: Aerial application, Part 137 - Operator: NE IA Helicopters, LLC - Registered owner: NE IA Helicopters, LLC - Airworthiness certificate: Standard, Normal; Special, Restricted (Special) - Last inspection: Annual, May 3, 2019, 106 hours before - Departed: Blair, NE - Destination: Blair, NE - Equipment: None ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 46; injuries: minor; commercial, flight instructor; instrument ratings: helicopter; medical: class 2, with waivers/limitations; last flight review April 12, 2019; seat: right; restraint: 3-point; flight hours: 3,162 total, 2,425 in this make and model, 3,089 as pilot in command, 170 in the last 90 days, 138 in the last 30 days, 15 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 180° at 10 knots - Visibility: 10 statute miles ## 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 20190727012669A](https://openairdocs.org/incident/20190727012669A), Jul 27, 2019: Robinson Helicopter Company R44 II, Blair, NE, Substantial damage. On 07/27/2019 at approximately 1608 LCL N7508Z, a Robinson R-44II s/n 10609, according to the pilot the helicopter experienced an engine RPM anomaly while… ## Docket (7 files) The files NTSB released with the investigation on March 30, 2020, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=99945. 4.3 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 2.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40481682&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Master.PDF - NTSB Examination Summary (item 2, .PDF, 163 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40481683&FileExtension=.PDF&FileName=NTSB%20Examination%20Summary-Master.PDF - NTSB Examination Cooling Fan (item 3, .PDF, 135 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40481684&FileExtension=.PDF&FileName=NTSB%20Examination%20Cooling%20Fan-Master.PDF - Excerpt of Maintenance Records (item 4, .PDF, 202 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40481685&FileExtension=.PDF&FileName=Excerpt%20of%20Maintenance%20Records-Master.PDF - RHC Service Bulletin 94 (item 5, .PDF, 163 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40481686&FileExtension=.PDF&FileName=RHC%20Service%20Bulletin%2094-Master.PDF - Photo Array (item 6, .PDF, 553 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40481687&FileExtension=.PDF&FileName=Photo%20Array-Master.PDF - RHC IPC Belt Tension Actuator (item 7, .PDF, 590 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40481688&FileExtension=.PDF&FileName=RHC%20IPC%20Belt%20Tension%20Actuator-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.