# NTSB WPR21LA313: Cessna 425, N783MB, Helena, MT, August 11, 2021 - Type: NTSB accident investigation - Classification: Accident · Serious injuries · Class 3 · Limited · Final report - Date: August 11, 2021, 09:00 local (15:00 UTC) - Place: Helena, MT · rural residential area - Coordinates: 46.740278, -111.94416 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=46.7403&lon=-111.9442&mi=10 - Phase of flight: [Emergency descent](https://openairdocs.org/ntsb-phases/600) (OpenAirDocs' grouping) - Defining event: [Emergency descent: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) - Highest injury: Serious injuries - Injuries: 3 serious - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Western Pacific Region - Parties: Federal Aviation Administration, Textron - Cessna - NTSB case key (mKey): 103681 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR21LA313 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/103681/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=103681 - Page: https://openairdocs.org/ntsb/WPR21LA313 ## Probable cause A flameout of both engines due to fuel starvation for reasons that could not be determined due to the airplane’s damage. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Power plant](https://openairdocs.org/ntsb-findings/01057100): Aircraft › Aircraft power plant · Unknown/Not determined (probable cause); cases with it: [Cessna 425, 1 case](https://openairdocs.org/ntsb-findings/01057100/cases.md?model=2076018), [All aircraft, 198 cases](https://openairdocs.org/ntsb-findings/01057100/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Emergency descent: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) (defining event); cases with it: [Cessna 425, 2 cases](https://openairdocs.org/ntsb-events/341/sequence.md?model=2076018), [All aircraft, 3,820 cases](https://openairdocs.org/ntsb-events/341/sequence.md) ## Analysis The pilot stated that on the morning of the accident he filled both wing fuel tanks to full. After takeoff, he climbed to his planned cruise altitude of 24,000 ft mean sea level (msl). While en route to his destination, the pilot reported that the left engine experienced a flame-out. The pilot opted to divert from the originally planned destination and descended. When the airplane was about 7,900 ft msl, the pilot reported that the right engine experienced a loss of power and that he was not going to be able to make it to the airport. Shortly thereafter, the airplane collided with trees and the airplane came to rest with the right wing and empennage severed from the fuselage. There was fuel in the wing tanks at the time of the impact. Postaccident examination of the wreckage did not reveal any anomalies. A partial amount of fuel was found in both of the filter bowls, but it is unknown if fuel was able to reach the engines. A complete examination of the fuel system could not be completed due to the damage incurred to the airplane at impact. Both engines flaming out within a short time of one another is likely indicative of a fuel supply or delivery issue; however, the nature of the problem could not be identified during postaccident examination. ## Factual narrative On August 11, 2021, about 0900 mountain daylight time, a Cessna 425 Conquest 1, N783MB, sustained substantial damage when it was involved in an accident near Helena, Montana. The pilot and two passengers sustained serious injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 business flight. The pilot stated that on the morning of the accident he refueled the airplane to full wing tanks by adding an additional 207 gallons of Jet A. Shortly thereafter, he departed from his home airport in Faribault, Minnesota and continued to his destination at a cruise altitude of 24,000 ft mean sea level. Air Traffic Control transmissions and automatic dependent surveillance-broadcast data indicate that, while en route at 0847:35, the pilot reported to an air traffic controller that the airplane had an engine [left engine] flame-out and requested a descent. The pilot opted to divert from the originally planned destination and contacted Helena approach control. He stated that the airplane was 16 miles from Helena and descending through 19,000 ft, advising the controller that he may need to lose altitude to land on runway 27. The controller responded that the pilot could maneuver north of the airport to align with the right base leg of the traffic pattern to the runway. At 0852:59 the pilot reported to the air traffic controller that he had an hour and a half of fuel on board and about 3 minutes later the airplane made a right turn to the north. At 0857:15, with the airplane about 7,900 ft msl, the pilot reported that the right engine experienced a loss of power (see Figure 1 below). At 0859:02, the pilot reported the airplane was going to collide with trees. The airplane came to rest with the right wing and empennage severed from the fuselage. There was fuel onboard the airplane at the time of impact, the quantity is unknown due to the fuel tanks being breached. The pilot estimated there was about 400 pounds in each tank at the time of the occurrence. Figure 1: Flight Track Plot The pilot noted that the airplane had undergone an annual inspection about 5 months before the accident, in March 2021. The airplane had accumulated about 20 flight hours since that inspection. During the examination of both the left and right engines, no evidence of a failure or anomaly was found. The left engine's compressor section showed the ability to rotate the first stage compressor wheel by hand, but the power section, specifically the propeller shaft, could not be manually rotated. The reduction gearbox had no damage to the case, but the propeller shaft was broken and the propeller flange was missing. Buckling was observed in the exhaust duct. The gas generator case, accessory gearbox, inlet case, and inlet screen were undamaged. The fuel control unit’s (FCU) connecting arm moved freely, but the reversing lever guide pin was bent and the carbon block was missing. The pneumatic lines, oil and fuel filters, power turbine (PT) blades, and first stageblades in the compressor section were intact and without damage. In the right engine, similar findings were observed with intact components in the compressor section, reduction gearbox, gas generator case, accessory gearbox, inlet case, and inlet screen. The power control linkage and reversing linkage were properly connected with intact hardware and safety mechanisms. The pneumatic lines, oil and fuel filters, PT blades, first stage blades in the compressor section, propeller shaft, and propeller retention bolts were undamaged. The controls and accessories, including the FCU, fuel pump, ignition system, fuel nozzles, flow divider, air system's bleed valve, propeller governor, and torque transducer, were all undamaged. Both fuel pumps were inspected, and no contamination was detected in the removed filters. A partial amount of fuel was found in both filter bowls. A complete examination of the fuel system could not be completed due to the damage incurred to the airplane at impact. According to the engine manufacturer, if an engine flames out in flight due to fuel starvation, it does not leave behind unique evidence different than a normal engine shut down. He added that both engines flaming out within a short time is not consistent with any dual-engine aircraft systemic design behaviors that could have occurred other than a fuel supply or delivery issue. ## Aircraft - Registration: [N783MB](https://openairdocs.org/aircraft/N783MB), registered now, S/N 425-0103, built 1982 (OpenAirDocs) - Reported make and model: CESSNA 425 - Registry model: [Cessna 425](https://openairdocs.org/model/cessna-425) (registry code 2076018) (OpenAirDocs) - Registry engine: [Pratt & Whitney PT6A series](https://openairdocs.org/engine/pratt-whitney-pt6a-series) (registry code 52032, turbo-prop) (OpenAirDocs) - Category: Airplane - Serial number: 425-0103 - Year built: 1982 - Airframe hours: 9576 - Engines: P&W PT6A-112 550 horsepower turbo prop; P&W PT6A-112 550 horsepower turbo prop - Damage: Substantial damage - Flight: Business, Part 91 - Airworthiness certificate: Standard, Normal - Last inspection: Annual, May 28, 2021, 10 hours before - Departed: FBL, Fairbault, MN - Destination: MSO, Missoula, MT - Flight plan: IFR - Airport: HLN, Helena Rgnl - Equipment: Onboard weather, Stall warning system, ADS-B, Auto-pilot, Electronic multifunction display, Electronic primary flight display ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 61; injuries: serious; private; airplane ratings: multi-engine land, single-engine sea, single-engine land; instrument ratings: airplane; medical: class 2, with waivers/limitations; seat: left; restraint: 3-point; flight hours: 6,000 total, 800 in this make and model ## Weather - Conditions: Visual (VMC), Day - Wind: 270° at 14 knots, gusting 25 - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 73 °F, dew point 46 °F - Altimeter: 30.03 inHg - Observed at: KHLN, 8 nm away - METAR: KHLN 111353Z 27014G25KT 10SM CLR 23/08 A3003 RMK AO2 PK WND 26030/1259 SLP143 T02330078 ## 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 20210811013679A](https://openairdocs.org/incident/20210811013679A), Aug 11, 2021: Cessna 425, Helena, MT, Substantial damage. On August 11, 2021 at 0905 MST, a Cessna CE-425, N783MB [privacy data omitted], lost engine power and crashed into trees approximately 9 miles north of Helena,… ## Docket (9 files) The files NTSB released with the investigation on September 20, 2023, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=103681. 13.2 MB in all. - Pilot/operator aircraft accident report, NTSB form 6120.1 (item 1, PDF, 8 pages, 2.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15880525&FileExtension=pdf&FileName=Z%20-%20Attachment%20A%20-%206120_Redacted-Rel.pdf - Investigation materials supplement (item 2, PDF, 12 pages, 855 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15908500&FileExtension=pdf&FileName=Z%20-%20Attachment%2001%20-%20Investigation%20Supplemental%20Material-Rel.pdf - Statement of party representatives to NTSB investigation (item 3, PDF, 1 page, 213 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15881008&FileExtension=pdf&FileName=party%20form_Redacted-Rel.pdf - Record of conversation (item 4, PDF, 1 page, 113 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15881592&FileExtension=pdf&FileName=Z%20-%20Attachment%2003%20-%20Record%20of%20Conversation-Rel.pdf - Summary of pilot's communications with air traffic control (item 5, PDF, 2 pages, 67 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15880555&FileExtension=pdf&FileName=Summary%20of%20Communications-Rel.pdf - Radar data (kml) (item 6, KML, 541 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15881539&FileExtension=kml&FileName=Garmin-Rel.kml - Radar data (tabular) (item 7, PDF, 719 pages, 6.7 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15906503&FileExtension=pdf&FileName=Radar%20Data-Rel.pdf - Electronic devices - specialist's factual report (item 8, PDF, 11 pages, 6 photos, 1.5 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16017267&FileExtension=pdf&FileName=Electronic%20Devices%20-%20Specialist%27s%20Factual%20Report-Rel.pdf - Electronic devices - attachment 1 (item 9, CSV, 981 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16016705&FileExtension=csv&FileName=Electronic%20Devices%20-%20Attachment%201-Rel.csv 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.