# NTSB CEN21LA390: Mantooth Thorp T-18, N78DW, San Antonio, TX, August 28, 2021 - Type: NTSB accident investigation - Classification: Accident · Minor injuries · Class 3 · Limited · Final report - Date: August 28, 2021, 15:37 local (20:37 UTC) - Place: San Antonio, TX - Coordinates: 29.643562, -98.614422 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=29.6436&lon=-98.6144&mi=10 - Phase of flight: [Initial climb](https://openairdocs.org/ntsb-phases/350) (OpenAirDocs' grouping) - Defining event: [Initial climb: Unknown or undetermined](https://openairdocs.org/ntsb-events/000) - Highest injury: Minor injuries - Injuries: 2 minor - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Central Region - Parties: FAA - SAIBs cited in the narratives: [SAIB CE-09-35](https://openairdocs.org/saib/CE-09-35) (OpenAirDocs) - NTSB case key (mKey): 103775 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CEN21LA390 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/103775/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=103775 - Page: https://openairdocs.org/ntsb/CEN21LA390 ## Probable cause The loss of engine power after takeoff for undetermined reasons. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Engine (reciprocating)](https://openairdocs.org/ntsb-findings/01058500): Aircraft › Aircraft power plant · Inoperative (probable cause); cases with it: [Mantooth THORP T-18, 1 case](https://openairdocs.org/ntsb-findings/01058500/cases.md?model=8951043), [All aircraft, 497 cases](https://openairdocs.org/ntsb-findings/01058500/cases.md) - [Temp/humidity/pressure: conducive to carburetor icing](https://openairdocs.org/ntsb-findings/03031030): Environmental issues › Conditions/weather/phenomena · Effect on operation (probable cause); cases with it: [Mantooth THORP T-18, 1 case](https://openairdocs.org/ntsb-findings/03031030/cases.md?model=8951043), [All aircraft, 435 cases](https://openairdocs.org/ntsb-findings/03031030/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Initial climb: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341); cases with it: [Mantooth THORP T-18, 1 case](https://openairdocs.org/ntsb-events/341/sequence.md?model=8951043), [All aircraft, 3,820 cases](https://openairdocs.org/ntsb-events/341/sequence.md) - [Initial climb: Unknown or undetermined](https://openairdocs.org/ntsb-events/000) (defining event); cases with it: [Mantooth THORP T-18, 1 case](https://openairdocs.org/ntsb-events/000/sequence.md?model=8951043), [All aircraft, 1,703 cases](https://openairdocs.org/ntsb-events/000/sequence.md) - [Emergency descent: Collision with terr/obj (non-CFIT) ](https://openairdocs.org/ntsb-events/470); cases with it: [Mantooth THORP T-18, 1 case](https://openairdocs.org/ntsb-events/470/sequence.md?model=8951043), [All aircraft, 10,189 cases](https://openairdocs.org/ntsb-events/470/sequence.md) - [Initial climb: Fuel related](https://openairdocs.org/ntsb-events/190); cases with it: [Mantooth THORP T-18, 1 case](https://openairdocs.org/ntsb-events/190/sequence.md?model=8951043), [All aircraft, 361 cases](https://openairdocs.org/ntsb-events/190/sequence.md) ## Analysis The pilot was planning a short cross-country flight with his passenger. Prior to takeoff, he fueled the airplane with 10-15 gallons of fuel and added one quart of oil to the engine. He performed an engine run-up that included checking the carburetor heat. The takeoff and initial climb were normal, but as he turned the airplane onto the downwind leg to depart the traffic pattern, the engine began running rough and lost total power. The pilot attempted to regain engine power by adjusting the engine mixture, but no change in engine performance was noted. Unable to maintain altitude, he performed a forced landing into trees. The airplane came to rest on its nose and sustained substantial damage. Postaccident examination of the engine revealed no evidence of any preimpact mechanical malfunctions or failures that would have precluded normal operation. Weather conditions reported at the time of the accident were conducive for serious carburetor icing at glide power. However, the pilot applied the carburetor heat during the engine run-up before takeoff, which should have either melted any ice that may have accumulated on the ground or resulted in a rough running engine, which the pilot did not report. The application of carburetor heat during the run-up combined with the high-power setting during takeoff and initial climb reduced the likelihood of carburetor ice. ## Factual narrative On August 28, 2021, about 1537 central daylight time, an experimental amateur-built Thorp T-18 airplane, N78DW, sustained substantial damage when it was involved in an accident near San Antonio, Texas. The pilot and passenger sustained minor injuries. The airplane was being operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to the pilot, he was planning a short cross-country flight with his passenger. Prior to takeoff, he fueled the airplane with 10 to15 gallons of fuel and added one quart of oil to the engine. He performed an engine run-up that included checking the carburetor heat and departed runway 17. The takeoff and initial climb were normal, but as he turned the airplane onto the downwind leg to depart the traffic pattern, the engine began running rough and lost total power. The pilot attempted to regain engine power by adjusting the engine mixture, but no change in engine performance was noted. Unable to maintain altitude, he performed a forced landing into trees. The airplane came to rest on its nose and sustained substantial damage to the forward fuselage and both wings. Postaccident examination by a Federal Aviation Administration (FAA) inspector revealed there was at least 2 gallons of fuel remaining in the single header-style fuel tank, which was punctured. Fuel was found in the carburetor bowl, and no contamination of the carburetor inlet screen was observed. The engine was rotated by hand through the propeller which produced compression/suction at each cylinder. All spark plugs were removed and exhibited normal wear signatures. The magnetos were removed for further examination. Examination of the left magneto revealed the internal components were damaged, and a weak spark was produced on two of the four towers when the magneto was rotated. The two other ignition towers were damaged. The right magneto would not rotate due to damage; the internal coil, capacitor, and points were undamaged, and no problems were noted. Examination of the engine revealed no evidence of preimpact mechanical anomalies that would have precluded normal engine operation. According to a carburetor ice probability chart, the atmospheric conditions at the time of the accident were conducive to serious icing at glide power. FAA Special Airworthiness Information Bulletin (CE-09-35) – Carburetor Icing Prevention, stated in part: …pilots should be aware that carburetor icing doesn't just occur in freezing conditions, it can occur at temperatures well above freezing temperatures when there is visible moisture or high humidity. Icing can occur in the carburetor at temperatures above freezing because vaporization of fuel, combined with the expansion of air as it flows through the carburetor, (Venturi Effect) causes sudden cooling, sometimes by a significant amount within a fraction of a second. Carburetor ice can be detected by a drop in rpm in fixed pitch propeller airplanes and a drop in manifold pressure in constant speedpropeller airplanes. In both types, usually there will be a roughness in engine operation. ## Aircraft - Registration: [N78DW](https://openairdocs.org/aircraft/N78DW), registered now, S/N 844, built 1980 (OpenAirDocs) - Reported make and model: MANTOOTH THORP T-18 - Registry model: [Mantooth THORP T-18](https://openairdocs.org/model/mantooth-thorp-t-18) (registry code 8951043) (OpenAirDocs) - Registry engine: [Lycoming 0-290 series](https://openairdocs.org/engine/lycoming-0-290-series) (registry code 41506, 4 cycle) (OpenAirDocs) - Category: Airplane, amateur-built - Serial number: 844 - Year built: 1980 - Airframe hours: 880 - Engines: Lycoming O-290-G 125 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Airworthiness certificate: Special, Experimental (Special) - Last inspection: Condition, November 15, 2021 - Destination: T82, Fredricksburg, TX - Airport: 5C1, Boerne Stage Airport - Equipment: Unknown ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 63; injuries: minor; commercial, flight instructor; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 2, without waivers/limitations; last flight review December 1, 2020; seat: left; restraint: 4-point; flight hours: 8,000 total, 43 in this make and model, 5,000 as pilot in command, 103 in the last 90 days, 24 in the last 30 days ## Weather - Conditions: Visual (VMC), Day - Wind: 290° at 10 knots - Visibility: 10 statute miles - Lowest ceiling: 4,100 ft broken - Temperature: 81 °F, dew point 73 °F - Altimeter: 29.92 inHg - Observed at: KSAT, 9 nm away - METAR: KSAT 282051Z 29010KT 10SM -RA BKN041 BKN065 BKN250 27/23 A2992 RMK AO2 RAB11 SLP114 P0006 60006 T02670233 56020= ## 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 20210828015119A](https://openairdocs.org/incident/20210828015119A), Aug 28, 2021: Mantooth THORP T-18, Boerne, TX, Destroyed. Pilot departure did not follow airport procedures, pilot took right turn as soon as air born, if continued straight emergency landing area would have been… ## Docket (5 files) The files NTSB released with the investigation on January 20, 2023, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=103775. 2.1 MB in all. - Pilot/operator aircraft accident report, NTSB form 6120.1 (item 1, PDF, 11 pages, 736 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=12747706&FileExtension=pdf&FileName=Pilot%206120_Redacted-Rel.pdf - Pilot statement (item 2, PDF, 1 page, 665 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=12743809&FileExtension=pdf&FileName=Pilot%20Statement_Redacted-Rel.pdf - Record of conversation FAA inspector (item 3, PDF, 1 page, 157 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=12747962&FileExtension=pdf&FileName=ROC%20Fricker%201-Rel.pdf - FAA SAIB carburetor icing prevention (item 4, PDF, 3 pages, 107 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=12748112&FileExtension=pdf&FileName=CE-09-35-Rel.pdf - Photograph (item 5, PDF, 1 page, 419 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=14959656&FileExtension=pdf&FileName=Photo%20Array-Rel%20(41)-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.