Beech S35 accident near Herman, Wisconsin, December 25, 2004
On December 25, 2004 at about 4:21 pm local time, a Beech S35, registered N5631K, was substantially damaged in an accident near Herman, Wisconsin. It was a personal flight under general aviation rules (Part 91). 2 people were killed. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
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.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- December 25, 2004 · about 4:21 pm local time
- Place
- Herman, Wisconsin · map
- Type
- Accident
- Injuries
- 2 people were killed.
- Weather
- visual conditions (good weather)
- Aircraft
- Beech S35 · all S35s on the register
- Registration
- N5631K · no longer on the register · serial D-7389
- Damage
- Substantial damage
- Flight
- Personal flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
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.
The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.
The factual record from the NTSB's investigation tables, in plain English
Pilot
- Certificate: airline transport pilot, flight instructor
- Ratings: multi-engine land; single-engine land; single-engine sea; instructor: airplane single-engine; instructor: instrument airplane; instrument: airplane
- Flight time: 4,516 hours in all; 643 in this make and model; 66 in the last 90 days; 51 in the last 30 days; 4,348 as pilot in command; 588 on instruments
- Last flight review: September 1, 2004
- Medical certificate: Class 3 (with waivers/limitations)
- Seat: left
- Injury: fatal
The aircraft
- Airframe total time: 5,616 hours
- Last inspection: annual inspection, June 1, 2004; 119 hours since
- Maximum gross weight: 3,300 lb
- Seats: 6
- Landing gear: retractable
- Engine: Continental IO-520-BA6B (piston); 0 hours total
- Fire on the ground
The flight
- Departed from: MTW Manitowoc WI at 4:06 pm
- Destination: LOT Romeoville IL
- Flight plan: IFR
Weather at the time
- Light: daylight
- Wind: from 220° at 5 knots
- Visibility: 7 statute miles
- Sky: overcast at 6,000 ft
- Temperature: 16°F (-9°C), dew point 7°F (-14°C)
- Altimeter: 30.03 inHg
- Observation at 4:53 pm from SBM
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Crew | 1 | |||
| Passengers | 1 |
Documents from the investigation the NTSB's docket: the evidence folder behind the report
The docket, the folder of records gathered during an investigation (maintenance records, photographs, witness statements, examinations), has not been read from the NTSB for this case yet; the list appears here once it has. Open the docket at the NTSB.
Everything on this page comes from the NTSB's public records. The narrative, probable cause and findings are the NTSB's own words; the coded tables behind the report are written out in plain English, with pilots' ages, home towns and medical details left out. The documents and photographs are the NTSB's docket, shown as the NTSB released them. This site's own text never names anyone involved. A preliminary report can change; the final report usually follows one to two years later, and the page is refreshed when it does.