# NTSB CEN19LA146: Sikorsky S76, N761AF, Morrilton, AR, May 15, 2019 - Type: NTSB accident investigation - Classification: Accident · No injuries · Class 3 · Limited · Final report - Date: May 15, 2019, 18:33 local (23:33 UTC) - Place: Morrilton, AR - Coordinates: 35.1018, -92.7652 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=35.1018&lon=-92.7652&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute-cruise: Powerplant sys/comp malf/fail](https://openairdocs.org/ntsb-events/340) - Highest injury: No injuries - Injuries: 6 uninjured - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Central Region - Parties: FAA - NTSB case key (mKey): 99455 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN19LA146 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/99455/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=99455 - Page: https://openairdocs.org/ntsb/CEN19LA146 ## Probable cause The improper securing of the exhaust duct bolts, which resulted in the duct becoming unseated and substantial heat damage to the tail rotor drive shaft. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Misc hardware: fasteners](https://openairdocs.org/ntsb-findings/01071430): Aircraft › Fluids/misc hardware · Incorrect service/maintenance (probable cause); cases with it: [Sikorsky S-76D, 1 case](https://openairdocs.org/ntsb-findings/01071430/cases.md?model=8143021), [All aircraft, 58 cases](https://openairdocs.org/ntsb-findings/01071430/cases.md) - [Engine exhaust](https://openairdocs.org/ntsb-findings/01057800): Aircraft › Aircraft power plant · Incorrect service/maintenance (probable cause); cases with it: [Sikorsky S-76D, 1 case](https://openairdocs.org/ntsb-findings/01057800/cases.md?model=8143021), [All aircraft, 56 cases](https://openairdocs.org/ntsb-findings/01057800/cases.md) - [Maintenance](https://openairdocs.org/ntsb-findings/02062000): Personnel issues › Task performance · Maintenance personnel (probable cause); cases with it: [Sikorsky S-76D, 1 case](https://openairdocs.org/ntsb-findings/02062000/cases.md?model=8143021), [All aircraft, 143 cases](https://openairdocs.org/ntsb-findings/02062000/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Enroute-cruise: Powerplant sys/comp malf/fail](https://openairdocs.org/ntsb-events/340) (defining event); cases with it: [Sikorsky S-76D, 1 case](https://openairdocs.org/ntsb-events/340/sequence.md?model=8143021), [All aircraft, 820 cases](https://openairdocs.org/ntsb-events/340/sequence.md) ## Analysis The pilot of the helicopter air ambulance flight reported that he experienced fumes in the cockpit while enroute, and shortly thereafter, received visual and aural warnings of smoke in the aft baggage compartment. The pilot initiated an emergency descent into an alternate airport, declared an emergency with air traffic control, and landed uneventfully. Examination of the helicopter revealed that the No. 2 engine exhaust duct was disconnected and unseated, which resulted in engine exhaust entering the compartment containing the tail rotor drive shaft and substantial heat damage to the drive shaft and surrounding areas. Examination of the No. 1 engine exhaust duct revealed that its attach bolts were not tightened to the specified torque value. Additionally, examination of the operator’s other helicopter revealed that the bolts securing both of its two exhaust ducts were not tightened to the specified torque value. The maintenance history of these components was not determined, but given the available information, it is likely that they were improperly secured, which resulted in their loosening and subsequently allowed the exhaust duct to become unseated. ## Factual narrative On May 15, 2019, about 1833 central daylight time, a Sikorsky S-76D helicopter, N761AF, sustained substantial damage while in cruise flight near Morrilton, Arkansas. The pilot, 2 crewmembers, and 3 passengers were not injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 135 on-demand air medical flight. The pilot reported that, 43 minutes into the flight, he experienced fumes in the cockpit. He turned the environmental control system off and immediately descended. Within seconds, he received visual and aural warnings of smoke in the aft baggage compartment. He initiated an emergency descent and declared an emergency with air traffic control and subsequently landed without further incident. A postaccident examination of the helicopter by a Federal Aviation Administration inspector revealed that the exhaust duct from the No. 2 engine was disconnected and not in its seated position. Exhaust from the No. 2 engine entered the compartment containing the tail rotor drive shaft and resulted in heat damage to drive shaft and surrounding areas. The exhaust ducts are attached using two bolts secured at 110 ft-lbs of pressure. Upon inspection of the No. 1 engine, as well as the operator’s second helicopter, all bolts were found partially disengaged and not tightened to the specified torque value. ## Aircraft - Registration: [N761AF](https://openairdocs.org/aircraft/N761AF), registered now, S/N 761039, built 2013 (OpenAirDocs) - Reported make and model: SIKORSKY S76 - Registry model: [Sikorsky S-76D](https://openairdocs.org/model/sikorsky-s-76d) (registry code 8143021) (OpenAirDocs) - Registry engine: [Pratt & Whitney Canada PW210S](https://openairdocs.org/engine/pratt-whitney-canada-pw210s) (registry code 52294, turbo-shaft) (OpenAirDocs) - Category: Helicopter - Serial number: 761039 - Year built: 2013 - Airframe hours: 2488 - Engines: Pratt and Whitney PW210S 1248 horsepower turbo shaft; Pratt and Whitney PW210S 1248 horsepower turbo shaft - Damage: Substantial damage - Flight: Business, Part 135 - Operator: Arkansas Childrens Hospital - Registered owner: Arkansas Childrens Hospital - Airworthiness certificate: Standard, Transport - Last inspection: Continuous airworthiness, March 13, 2019, 205 hours before - Departed: 14AR, Springdale, AR - Destination: AR62, Little Rock, AR - Flight plan: Company VFR - Airport: BDQ, Morrilton Muni, runway 09/27, 4,000 × 75 ft, asphalt - Equipment: Auto-pilot, Data recorder, Electronic flight bag or handheld device, Electronic multifunction display, Electronic primary flight display, Onboard weather, Satellite tracking device ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 50; injuries: none; airline transport, commercial; airplane ratings: single-engine land, multi-engine sea; instrument ratings: airplane, helicopter; medical: class 1, without waivers/limitations; last flight review March 28, 2019; seat: right; restraint: 5-point; flight hours: 6,518 total, 431 in this make and model, 5,165 as pilot in command, 32 in the last 90 days, 13 in the last 30 days, 4 in the last 24 hours - Other flight crew; seat: rear; restraint: 4-point - Other flight crew; seat: rear; restraint: 4-point ## Weather - Conditions: Visual (VMC), Day - Wind: 300° at 4 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 84 °F, dew point 64 °F - Altimeter: 29.90 inHg - Observed at: KRUE, 25 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 20190515011089A](https://openairdocs.org/incident/20190515011089A), May 15, 2019: Sikorsky Aircraft Corp S-76D, Morrilton, AR, Substantial damage. On Wednesday, may 15, 2019, at approximately 1830 CDT, N761AF, registered to Arkansas children? Hospital, and operated by Arkansas children?s hospital (Z1RA),… ## Other investigations on N761AF (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 CEN22LA147](https://openairdocs.org/ntsb/CEN22LA147), Mar 13, 2022: Sikorsky S-76D (N761AF), Texarkana, AR, substantial damage. Probable cause: The pilot’s failure to maintain adequate clearance during landing on a rooftop helipad. ## Docket (3 files) The files NTSB released with the investigation on October 5, 2021, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=99455. 8.7 MB in all. - Pilot/operator aircraft accident report, NTSB form 6120.1 (item 1, PDF, 11 pages, 5.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=12305840&FileExtension=pdf&FileName=CEN19LA146%206120%20completed%20w%20blocks%20filled%20for%20docket_Redacted-Rel.pdf - Record of conversation with FAA inspector (item 2, PDF, 1 page, 123 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=12306390&FileExtension=pdf&FileName=Record%20of%20Conversation%20with%20FAA-Rel.pdf - Photographs (item 3, PDF, 2 pages, 3.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=12305926&FileExtension=pdf&FileName=Photographs-Rel.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.