# NTSB WPR22LA005: Beech B36TC, N7220B, Los Banos, CA, October 9, 2021 - Type: NTSB accident investigation - Classification: Accident · No injuries · Class 3 · Limited · Final report - Date: October 8, 2021, 19:04 local (Oct 9, 2021, 02:04 UTC) - Place: Los Banos, CA · 1 miles south in open terrain - Coordinates: 37.042261, -120.86175 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=37.0423&lon=-120.8618&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute-cruise: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Western Pacific Region - Parties: Federal Aviation Administration - NTSB case key (mKey): 104084 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR22LA005 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/104084/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=104084 - Page: https://openairdocs.org/ntsb/WPR22LA005 ## Probable cause The total loss of engine power due to the improper installation of the No. 4 connecting rod bolt nut during a recent overhaul. ## 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 · Incorrect service/maintenance (probable cause) - [Maintenance/inspections: unscheduled maint checks](https://openairdocs.org/ntsb-findings/01010550): Aircraft › Aircraft handling/service · Incorrect service/maintenance (probable cause) - [Maintenance: installation](https://openairdocs.org/ntsb-findings/02062035): Personnel issues › Task performance · Maintenance personnel (probable cause) ## Analysis The pilot reported that he was on the return leg of a cross country flight, about 10,000 ft mean sea level, when the engine lost oil pressure and the manifold pressure dropped. He immediately diverted to the nearest airport. While in the descent to his divert location, the engine was initially producing partial power, but then exhibited serious vibrations and subsequently lost all power. During this time, the cockpit filled with smoke, and fire and sparks were observed exiting from the engine cowling. Due to the fire, the pilot elected to make a forced landing on a road near the approach end of runway. The airplane struck an object during the landing roll which resulted in substantial damage to the wings. A postaccident examination of the engine revealed that the No. 4 connecting rod bolt nut was missing. Prominent thermal distress was observed in the area where the No. 4 connecting rod connected to the crankshaft and was consistent with oil starvation. In June of 2020, the engine was disassembled for a propeller strike inspection. The inspection was about 27.3 hours before the accident. As part of the inspection, the connecting rods were overhauled and then reinstalled on the crankshaft using new bearings, rod bolts, and nuts. Given the recency of the work, it is likely that insufficient torque was applied during installation of the No. 4 connecting rod bolt nut, which subsequently became loose and separated. ## Factual narrative On October 8, 2021, about 1904 Pacific daylight time, a Beech B36TC airplane, N7220B, was substantially damaged when it was involved in an accident near Los Banos, California. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that he flew the airplane to Paso Robles Municipal Airport (PRB), Paso Robles, California, where he refueled and was on his return flight to Gnoss Field Airport (DVO), Novato, California, when the accident occurred. The airplane was at about 10,000 ft mean sea level when the engine lost oil pressure and the manifold pressure dropped. He immediately diverted to Los Banos Municipal Airport (LSN), Los Banos, California. While in the descent into LSN, the engine was initially producing partial power, but then exhibited severe vibrations and subsequently lost all power. During this time, the cockpit filled with smoke, and fire and sparks were observed coming from the engine cowling. Due to the fire, the pilot elected to make a forced landing on a road near the approach end of the runway. The airplane struck an object during the landing roll, which caused the airplane to spin around before coming to rest. A review of engine data from a Garmin G500TXi device revealed that the airplane leveled off and the engine was set to about 2,500 rpm. About 9 minutes later, the engine’s oil pressure started to decrease, while the engine rpm was unchanged. In the next 12 minutes, the oil pressure continued to decrease and culminated with the engine rpm decreasing from about 2,371 to zero rpm in about 5 seconds while the airplane was in a descent. Postaccident examination of the engine revealed external damage with an exit hole on the crankcase near the top of the No. 2 cylinder. The hole was about 2 inches wide by 3 inches long. A second hole in the crankcase was noted on the left back side that had a diameter of about 1 inch. Additionally, several large cracks in the crankcase were observed on both crankcase halves. All engine accessories on the back side of the engine remained attached except for the left magneto. The rocker covers were removed and there was evidence of heat distress on all cylinders. Rotational continuity could not be established due to the crankshaft damage. Disassembly of the engine revealed that the No. 4 connecting rod bolt nut was missing. Thermal distress was observed in the area where the No. 4 connecting rod connected to the crankshaft, consistent with oil starvation. The thermal distress in this area was the most prominent in the engine. Considerable metal debris was noted in the oil sump and oil filter. The engine was installed in July of 2012, and logged about 671 hours of time before the accident. In June of 2020, the engine was disassembled for a propeller strike inspection. The inspection was about 27.3 hours before the accident. As part of the inspection, the connecting rods were overhauled by a third-party vendor, andthen the vendor reinstalled the connecting rods on the crankshaft using new bearings, rod bolts, and nuts. The most recent annual inspection was accomplished in September of 2021, about 2.3 hours before the accident. ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Enroute-cruise: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) (defining event) - [Enroute-cruise: Emergency descent initiated](https://openairdocs.org/ntsb-events/130) - [Approach: Off-field or emergency landing](https://openairdocs.org/ntsb-events/440) ## Aircraft - Registration: [N7220B](https://openairdocs.org/aircraft/N7220B), registered now, S/N EA-425, built 1984 (OpenAirDocs) - Reported make and model: BEECH B36TC - Registry model: [Beech B36TC](https://openairdocs.org/model/beech-b36tc) (registry code 1151609) (OpenAirDocs) - Registry engine: [NONE](https://openairdocs.org/engine/none) (registry code 00000, none) (OpenAirDocs) - Category: Airplane - Serial number: EA-425 - Year built: 1984 - Airframe hours: 5356.9 - Engines: Continental IO550B-AP 300 horsepower reciprocating - Damage: Substantial damage - Flight: Business, Part 91 - Registered owner: 6l6 LLC - Airworthiness certificate: Standard, Normal - Last inspection: Annual, September 8, 2021 - Departed: PRB, Paso Robles, CA - Destination: DVO, Novato, CA - Flight plan: IFR - Airport: LSN, Los Banos Muni - 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 43; injuries: none; private; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 3, with waivers/limitations; last flight review March 15, 2021; seat: left; restraint: 3-point; flight hours: 1,353.3 total, 927.6 in this make and model, 1,469.6 as pilot in command, 17.3 in the last 90 days, 3.8 in the last 30 days, 2 in the last 24 hours ## Weather - Conditions: Visual (VMC), Dusk - Wind: 230° at 8 knots, gusting 14 - Visibility: 10 statute miles - Temperature: 57 °F, dew point 46 °F - Altimeter: 30.14 inHg - Observed at: KCVH, 28 nm away - METAR: KCVH 090215Z AUTO 23008G14KT 10SM FEW050 14/08 A3014 RMK A01 ## 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 20211008017449A](https://openairdocs.org/incident/20211008017449A), Oct 8, 2021: Beech B36TC, Los Banos, CA, Substantial damage. On oct 8, 2021, N7220B departed paso robles airport. While enroute, at cruise altitude, the engine began to loose power. The PIC noticed the oil pressure had… ## Docket (5 files) The files NTSB released with the investigation on October 19, 2023, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=104084. 5.4 MB in all. - Pilot/operator aircraft accident report, NTSB form 6120.1 (item 1, PDF, 9 pages, 1.5 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16126942&FileExtension=pdf&FileName=NTSB%206120_Redacted-Rel.pdf - Engine examination summary report (item 2, PDF, 7 pages, 680 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16166969&FileExtension=pdf&FileName=WPR22LA005%20Engine%20Examination%20Summary%20Report%20Final%201-Rel.pdf - Engine data (item 3, CSV, 1.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16129414&FileExtension=csv&FileName=log_211009_011706_KPRB-Rel.csv - Engine logbook excerpts (item 4, PDF, 2 pages, 1.7 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16130314&FileExtension=pdf&FileName=Engine%20Logbook%20Excerpts%20Final%201_Redacted-Rel.pdf - Release of aircraft wreckage, NTSB form 6120.15 (item 5, PDF, 1 page, 234 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16126675&FileExtension=pdf&FileName=2022%20Retention-Release-of-Wreckage-Form%20-%20SIGNED_Redacted-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.