CHI05FA048 · Beech S35
Beech S35 · Accident: total loss of engine power (mechanical failure) en route
From Manitowoc County Airport (MTW) to Lewis University Airport (LOT)
Event
- NTSB case
- CHI05FA048
- Event typeAccident: someone killed or seriously injured, or the aircraft substantially damaged (NTSB definition). Incident: an occurrence that affected or could have affected safety, short of that. Glossary
- Accident
- InvestigationHow far the investigation had got when the record was published: preliminary, ongoing, final or completed. Unknown where the source does not say. Glossary
- Completed
- API-reported fatalities
- 2 · all aircraft and ground
- Ground fatalities
- Unknown
- OperationWhat kind of flying it was, grouped by the rules it flew under: airline (US Part 121), air taxi and commuter (Part 135), general aviation (Part 91 and similar), military or government. Glossary
- General aviation
- WeatherVisual meteorological conditions (VMC): good enough to fly by looking outside. Instrument conditions (IMC): cloud or low visibility, flying by instruments. Glossary
- Visual Meteorological Cond
Beech S35
- Aircraft type
- Beechcraft 35
- Category
- Airplane
- RegistrationThe aircraft's tail number, such as N12345 or G-ABCD. Registrations are reissued, so the same one years apart can be a different aircraft. Glossary
- N5631K
- Operator
- Unknown
- Onboard fatalities
- Unknown
- Route
- From Manitowoc County Airport (MTW), Manitowoc, WITo Lewis University Airport (LOT), Romeoville, IL
- Aircraft age
- Not recorded
- Flight rulesThe regulations the flight operated under: in the US, Part 91 (general aviation), Part 121 (airlines), Part 135 (air taxi and commuter) and others; for flights abroad, the NTSB's coarser commercial or non-commercial code. Glossary
- Part 91: General Aviation
- Phase of flightThe stage of the flight when things started to go wrong: standing, taxi, takeoff, initial climb, en route, maneuvering, approach or landing. Glossary
- En route · cruise
- First occurrenceThe single coded event the NTSB judges best describes what happened (records from 2008 on). Older records name the first occurrence in the sequence instead. Glossary
- Total loss of engine power (mechanical failure)
- Also codedOther events the NTSB coded in the sequence, such as a wire strike after a loss of power. Flight Findings uses them for its kinds of event. Glossary
- Tree(s)
- DamageDestroyed: beyond practical repair. Substantial: damage that affects the structure, performance or handling and normally needs major repair. Minor: less than that. Glossary
- Substantial
Cause areas
- Engine assembly, other › Improper
- Other maintenance personnel › Maintenance, installation, improper
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
The airplane collided with trees and terrain during a forced landing following a loss of engine power. Approximately 8 minutes after taking off, the pilot reported to air traffic control that the cabin of his airplane was filling with smoke and he was diverting to a near-by airport. The airplane contacted 30 to 40 foot tall trees which bordered an open field. The airplane then contacted the terrain and a post impact fire ensued. Inspection of the engine revealed two holes in the crankcase near the number four cylinder with the number four piston rod separated from the crankshaft. Teardown of the engine revealed five cylinder deck stud nuts were missing and the number five cylinder seventh stud had sheared. The crankshaft, counterweights, and rod bearings exhibited thermal damage which was most prominent at the number four cylinder connecting rod journal. Material from the number four connecting rod bearing was fused to the crankshaft journal displacing the oil tube toward the number three main journal. The cylinders had been removed and overhauled approximately 380 hours prior to the accident. The cylinder base packings on all of the cylinders were flattened and extruded between the base of the cylinders and the crankcase. The cross section diameter of the packings was larger than a sample packing, part number 641066, which is used on IO-520-BA engines. The cross section diameter of the base packings that were removed from the engine were similar in diameter to those used on the O-470 series engines.
Probable cause
The installation of the improper cylinder base packing seals by maintenance personnel resulting in the loss of lubriation and subsequent failure of the number four connecting rod/bearing. A factor associated with the accident was the trees that the airplane contacted during the forced landing.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record CHI05FA048
- Event ID
- 20041228X02038
- Case number
- CHI05FA048
- Dataset
- historical-pre2008
- Source SHA-256
- 89e2df6d848e7ab3b42e7d7c7a03ff403303057a26ca04c95b3ea67201c3ce74
Source notes (4)
- Unreviewed is an editorial label, not an investigation status. API-sourced is not report-checked or human-reviewed. Explicit event totals are used without summing aircraft injury tables; onboard allocation is withheld. Unknown values remain unknown. The operation category is mapped from the NTSB-reported FAR part and has not been reviewed.
- Filled from the NTSB case API where the bulk record had no value: investigation status. Values present in the bulk record are kept.
- The date is the local date, which is the same as the UTC date the NTSB stores.
- API snapshot SHA-256: 6aa5ec3cf610ef1149b8704dc40d24a4fea94871cbe244db0c8b7f2216c0c2f1; retrieved 2026-09-20T18:10:19.190Z.