# NTSB WPR19LA176: Cessna 172, N64460, Fullerton, CA, June 21, 2019 - Type: NTSB accident investigation - Classification: Accident · No injuries · Class 3 · Limited · Final report - Date: June 20, 2019, 17:16 local (Jun 21, 2019, 00:16 UTC) - Place: Fullerton, CA - Coordinates: 33.869998, -117.990837 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=33.8700&lon=-117.9908&mi=10 - Phase of flight: [Takeoff](https://openairdocs.org/ntsb-phases/300) (OpenAirDocs' grouping) - Defining event: [Takeoff: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342) - Highest injury: No injuries - Injuries: 2 uninjured - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Western Pacific Region - Parties: Federal Aviation Adminstration FSDO - NTSB case key (mKey): 99682 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR19LA176 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/99682/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=99682 - Page: https://openairdocs.org/ntsb/WPR19LA176 ## Probable cause Partial loss of engine power during takeoff due to an age-degraded carburetor heat valve seal, which detached and partially blocked the carburetor air inlet. Contributing to the accident was an inadequate maintenance inspection. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Power plant: air intake](https://openairdocs.org/ntsb-findings/01057160): Aircraft › Aircraft power plant · Damaged/degraded (probable cause); cases with it: [Cessna 172M, 1 case](https://openairdocs.org/ntsb-findings/01057160/cases.md?model=2072418), [All aircraft, 50 cases](https://openairdocs.org/ntsb-findings/01057160/cases.md) - [Power plant: air intake](https://openairdocs.org/ntsb-findings/01057160): Aircraft › Aircraft power plant · Fatigue/wear/corrosion (probable cause); cases with it: [Cessna 172M, 1 case](https://openairdocs.org/ntsb-findings/01057160/cases.md?model=2072418), [All aircraft, 50 cases](https://openairdocs.org/ntsb-findings/01057160/cases.md) - [Maintenance: scheduled/routine maintenance](https://openairdocs.org/ntsb-findings/02062010): Personnel issues › Task performance · Maintenance personnel (probable cause); cases with it: [Cessna 172M, 3 cases](https://openairdocs.org/ntsb-findings/02062010/cases.md?model=2072418), [All aircraft, 320 cases](https://openairdocs.org/ntsb-findings/02062010/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Takeoff: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342) (defining event); cases with it: [Cessna 172M, 16 cases](https://openairdocs.org/ntsb-events/342/sequence.md?model=2072418), [All aircraft, 1,858 cases](https://openairdocs.org/ntsb-events/342/sequence.md) - [Emergency descent: Collision with terr/obj (non-CFIT) ](https://openairdocs.org/ntsb-events/470); cases with it: [Cessna 172M, 100 cases](https://openairdocs.org/ntsb-events/470/sequence.md?model=2072418), [All aircraft, 10,189 cases](https://openairdocs.org/ntsb-events/470/sequence.md) ## Analysis Shortly after takeoff during a practice go-around, the engine lost partial power. With limited time to troubleshoot, the flight instructor maneuvered the airplane for an off-airport landing, and the airplane sustained substantial damage after impacting a street. Postaccident examination revealed that the aft section of the carburetor heat butterfly valve seal had detached and partially blocked the air inlet of the carburetor venturi. The obstruction reduced the amount of air available for combustion, resulting in a rich fuel-to-air mixture, and partial loss of power. The valve seal was composed of a fiber-reinforced rubberized material that degraded and became brittle over the 45-year life of the airplane. The mechanic who performed the last inspection stated that he confirmed the operation and condition of the butterfly valve by observing it through both the airbox assembly forward inlet and the heated air inlet on the rear right side of the unit. He stated that the aft section of the seal is hard to view due to the way it folds behind the butterfly valve and that the only way to clearly see it is through the heated air inlet, which was small. ## Factual narrative On June 20, 2019, at 1716 Pacific daylight time a Cessna 172M, N64460, was substantially damaged when it was involved in an accident near Fullerton Municipal Airport (FUL), Fullerton, California. The flight instructor and pilot receiving instruction were not injured. The airplane was operated under the provisions of Title 14 Code of Federal Regulations Part 91 as a local instructional flight. The flight instructor reported that he planned to perform a flight review of the pilot receiving instruction and remain within the traffic pattern. He confirmed that both fuel tanks were full prior to departure and that the engine contained over 5 quarts of oil. The preflight checks and the engine runup did not reveal any anomalies. After completing one circuit in the traffic pattern, they performed a practice go-around. During the initial takeoff climb of the maneuver, the engine began to lose partial power. The flight instructor took the airplane's controls and applied carburetor heat. The engine responded for a few seconds, and then power was lost again. With minimal climb performance available, and limited time to perform trouble shooting steps, the instructor decided to land the airplane on a road adjacent to the airport. The airplane sustained damage to the right wing and forward fuselage during the off-airport landing. The airplane was equipped with an airbox assembly mounted to the carburetor venturi inlet on the underside of the engine. Inlet air passed through a filter on the front of the airbox and was directed up into the carburetor venturi by a butterfly valve. The system was designed such that when the pilot pulled the carburetor heat control (ON), the butterfly valve rotated about 90°, and redirected heated air from an exhaust shroud into the carburetor venturi through the back of the airbox. The butterfly valve was composed of two metal plates that sandwiched a flexible fiber-reinforced rubberized seal. Examination of the airbox assembly revealed that the aft section of the carburetor heat butterfly valve seal had broken away from the valve, and partially obstructed the air inlet of the carburetor venturi (See figures 1 and 2). The section was about 4 1/2 inches long and 3/8-inch-wide. It was brittle and exhibited four holes that matched the location of rivets on the lower side of the airbox (See figure 3). Black sooting was also observed on the inner surfaces of the exhaust pipe and the electrodes of all spark plugs (See figure 4). Figure 1 – Carburetor Heat Valve Seal Fragment Obstructing Carburetor Inlet Venturi Figure 2 – Carburetor Heat Valve in the ON Position (Area of Missing Seal Highlighted) Figure 3 – Carburetor Heat Valve Seal Fragment Figure 4 – Top Spark Plugs According to maintenance logbooks, the last inspection was an annual inspection completed 73.5 flight hours before the accident on May 16, 2019, at a total airframe time of 3,052.5 hours. The Cessna 172 service manual recommended that the induction airbox, air valves,doors and controls be inspected at 100-hour intervals. The mechanic who performed the last inspection stated that he confirmed the operation and condition of the butterfly valve by observing it through both the airbox assembly forward inlet and the heated air inlet on the rear right side of the unit. He stated that the aft section of the seal is hard to view due to the way it folds behind the butterfly valve and that the only way to clearly see it is through the heated air inlet, which was small. The only documented maintenance performed on the airbox assembly since the airplane’s manufacture in 1974 was the replacement of the airbox induction filter shroud on June 13, 2017. Review of the Federal Aviation Administration's Service Difficulty Report (SDR) database revealed three similar occurrences involving carburetor-equipped Cessna airplanes. Two occurred in 1977/78 N model 172's and one in a 1974 M model. The total time in service of the affected components was 3,706, 4,925, and 7,993 hours respectively. ## Aircraft - Registration: [N64460](https://openairdocs.org/deregistered/N64460-2021-06-05), registration cancelled 2021-06-05, S/N 17265247 (OpenAirDocs) - Reported make and model: Cessna 172 (M) - Registry model: [Cessna 172M](https://openairdocs.org/model/cessna-172m) (registry code 2072418) (OpenAirDocs) - Registry engine: [Lycoming 0-320 series](https://openairdocs.org/engine/lycoming-0-320-series) (registry code 41508, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 17265247 - Year built: 1974 - Airframe hours: 2952.2 - Engines: Lycoming O-320 SERIES 150 horsepower reciprocating - Damage: Substantial damage - Flight: Instructional, Part 91 - Airworthiness certificate: Standard, Utility; Standard, Normal - Last inspection: Annual, May 16, 2019, 74 hours before - Departed: FUL, Fullerton, CA - Destination: FUL, Fullerton, CA - Airport: FUL, Fullerton Muni, runway 24, 3,121 × 75 ft, asphalt - Equipment: Stall warning system, Electronic flight bag or handheld device ## Flight crew As NTSB recorded them. NTSB leaves out names. - Flight instructor; age 35; injuries: none; commercial, flight instructor; airplane ratings: single-engine land; instrument ratings: airplane; medical: class 1, without waivers/limitations; last flight review May 1, 2019; seat: right; restraint: 3-point; flight hours: 1,408 total, 1,355 in this make and model, 1,350 as pilot in command, 122 in the last 90 days, 44 in the last 30 days - Pilot; age 33; injuries: none; private; airplane ratings: single-engine land; medical: class 3, without waivers/limitations; last flight review March 6, 2017; seat: left; restraint: 3-point; flight hours: 92 total, 89 in this make and model, 47 as pilot in command, 0 in the last 90 days, 0 in the last 30 days, 0 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 150° at 8 knots - Visibility: 10 statute miles - Lowest ceiling: 3,000 ft overcast - Temperature: 70 °F, dew point 55 °F - Altimeter: 29.90 inHg - Observed at: KFUL, 1 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 20190620007599A](https://openairdocs.org/incident/20190620007599A), Jun 20, 2019: Cessna 172M, Fullerton, CA, Substantial damage. During a go-around, attempting to climb, the engine sputtered and lost significant power. Pilot landed aircraft off-field. ## Docket (7 files) The files NTSB released with the investigation on May 10, 2022, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=99682. 10.8 MB in all. - Pilot/operator aircraft accident report, NTSB form 6120.1 (item 1, PDF, 9 pages, 3.5 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=8555960&FileExtension=pdf&FileName=r_6120_Redacted-Rel.pdf - Mechanic interview (item 2, PDF, 1 page, 85 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=8555819&FileExtension=pdf&FileName=INTERVIEW%20SUMMARY-Rel.pdf - Maintenance logbook excerpts (item 3, PDF, 6 pages, 5.7 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=8555184&FileExtension=pdf&FileName=r_Maint%20Excerpts_Redacted-Rel.pdf - Service difficulty reports (item 4, PDF, 6 pages, 19 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=8555480&FileExtension=pdf&FileName=Service%20Difficulty%20Reports-Rel.pdf - Maintenance manual excerpts (item 5, PDF, 1 page, 76 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=8555634&FileExtension=pdf&FileName=172%201969%20-%201976%20inspection%205-Rel.pdf - Evidence control form (item 6, PDF, 1 page, 219 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=8556026&FileExtension=pdf&FileName=Evidence%20Control%20Form%20-WPR19LA176-Rel.pdf - Photos (item 7, PDF, 8 pages, 8 photos, 1.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=8555625&FileExtension=pdf&FileName=Photos-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.