Beech C23 accident near Merrill, Wisconsin, May 11, 2021
On May 11, 2021 at about 8:00 pm local time, a 1979 Beech C23, registered N793Y, was substantially damaged in an accident during enroute (descent) near Merrill, Wisconsin (Merrill Municipal Airport). It was a personal flight under general aviation rules (Part 91). 2 people had minor injuries. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
The loss of engine power due to tappet failure.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- May 11, 2021 · about 8:00 pm local time
- Place
- Merrill, Wisconsin · Merrill Municipal Airport · map
- Type
- Accident
- Injuries
- 2 people had minor injuries.
- Weather
- visual conditions (good weather)
- Aircraft
- Beech C23, built 1979 · all C23s on the register
- Registration
- N793Y · registry record · serial M-2184
- Damage
- Substantial damage
- Flight
- Personal flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
The pilot reported that he was returning to the airport after a 1-hour flight when the engine started to run rough and gradually lost power. The pilot switched fuel tanks and cycled the magnetos, with no change in the power loss. He executed an off airport forced landing. The landing gear collapsed during the landing and the airplane slid to a stop coming to rest upright. The airplane sustained substantial damage to both wings and fuselage. Examination of the engine found that the oil filter contained metallic particles that were determined to be consistent with tappet material. Further examination revealed 7 of the 8 tappets were destroyed. A metallurgical examination of the tappets revealed that the tappets fractured from overstress. The fracture started along the heads facing their corresponding camshaft lobes, which proceeded towards the back surface. While there were no indications of pre-existing cracks, such as from fatigue, there was evidence of pitting and surface wear on many of the tappet head faces that contact the camshaft. Of note was the No.2 exhaust tappet, the only tappet that underwent wear on the tappet face significant enough to change its geometry. The engine was overhauled 19 years before the accident and had accumulated 838 hours since the overhaul. The engine manufacturer recommends overhaul of the engine at 2,000 hours, or 12 years in service, whichever comes first. No record of tappet replacement was found in the maintenance records.
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
What happened, in order
- Loss of engine power (partial) during enroute (descent) defining event
The NTSB's findings
- Aircraft › Aircraft power plant › Engine (reciprocating) › Recip eng cyl section › Failure
Pilot
- Certificate: private
- Ratings: single-engine land
- Flight time: 233 hours in all; 136 in this make and model; 25 in the last 90 days; 9 in the last 30 days; 77 as pilot in command
- Last flight review: April 15, 2021
- Medical certificate: Class 3 (with waivers/limitations)
- Seat: left
- Injury: no injuries
The aircraft
- Airframe total time: 4,419.3 hours
- Last inspection: 100-hour inspection, February 24, 2021; 55.7 hours since
- Maximum gross weight: 2,450 lb
- Seats: 4
- Landing gear: fixed
- Engine: Lycoming O-360-A2G (piston); 4,055 hours total
The flight
- Flight plan: none
Weather at the time
- Light: daylight
- Wind: from 020° at 3 knots, gusting 14
- Visibility: 10 statute miles
- Sky: scat at 7,000 ft
- Temperature: 55°F (13°C), dew point 25°F (-4°C)
- Altimeter: 30.31 inHg
- Observation at 2:55 pm from RRL, 5 miles away
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Flight crew | 1 | |||
| Passengers | 1 |
Documents from the investigation the NTSB's docket: the evidence folder behind the report
8 documents, released by the NTSB on August 15, 2023. View them here, or download them; the NTSB redacts some personal details before release, and this site shows the NTSB's own titles rather than its file names.
| # | Document | What it is | |
|---|---|---|---|
| 1 | Pilot/operator Aircraft Accident Report, NTSB Form 6120.1 | PDF, 9 pages | View Download |
| 2 | On Scene Photos | PDF, 3 pages | View Download |
| 3 | Engine Examination Summary | PDF, 3 pages | View Download |
| 4 | Materials Laboratory Factual Report | PDF, 26 pages | View Download |
| 5 | Maintenance Records | PDF, 3 pages | View Download |
| 6 | Maintenance 2-YEAR History | PDF, 15 pages | View Download |
| 7 | Memorandum for Record A�� Telephone Interview, Maintenance | PDF, 1 page | View Download |
| 8 | Oil Sample Report | PDF, 1 page | View Download |
The same docket at the NTSB · documents without a copy here are fetched from the NTSB when you open them.
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.