Beech C23 accident near Oak Shores, California, April 28, 2002
On April 28, 2002, a Beech C23, registered N9180S, was destroyed in an accident near Oak Shores, California. It was an instructional flight under general aviation rules (Part 91). 3 people were killed and 1 person was seriously injured. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
the number 1 cylinder exhaust valve fractured and separated resulting in a loss of engine power and an off airport forced landing. A finding in the accident was the owner's failure to maintain the engine in accordance with the manufacturer's recommendations.
Source: NTSB aviation accident database, copy made October 4, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- April 28, 2002
- Place
- Oak Shores, California · map
- Type
- Accident
- Injuries
- 3 people were killed and 1 person was seriously injured.
- Weather
- visual conditions (good weather)
- Aircraft
- Beech C23 · all C23s on the register
- Registration
- N9180S · registry record · serial M-1801
- Damage
- Destroyed
- Flight
- Instructional flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
The airplane collided with trees following a loss of engine power. A passenger heard a "roar" through the four-way intercom. The certified flight instructor (CFI) and the student pilot checked the oil pressure and fuel pressure; both were "good." The CFI pointed to the left and directed the student toward a private strip. During or immediately following the left turn, the CFI said, "I've got it." The student looked back at the two passengers, and motioned with his right hand that they were going to land at the strip. The last thing that the passenger remembered was contact with the trees and coming to rest. The airplane cleared a ridge top, but collided with trees about 1/4 mile from the landing strip. The spark plug for cylinder no. 1 sustained mechanical damage and contained metallic debris. The head of the cylinder no. 1 exhaust valve was missing, and the top of the piston exhibited mechanical damage across its entire surface. Metallurgists examined the valve and cylinder. The valve stem was broken and remained in the valve guide. The stem fractured and there were numerous secondary cracks below the fracture surface. The areas around the valve seats were severely damaged. The fracture surface condition was such that the fracture mechanism could not be determined. The secondary cracks were only in a local area where the material was severely battered and deformed. Many of the cracks were slightly curved and/or did not appear to be perpendicular to the outer or inner surface. These types of cracks are most likely to occur where surfaces have overlapped, or are the result of the excessive local strains in the area. There were no material or dimensional abnormalities that would suggest fatigue. The manufacturer issued maintenance instructions describing methods for determining exhaust valve and guide condition. This maintenance function was optional for the operator, and maintenance records indicated that this had not been done. Although the diameter of the exhaust valve stem was slightly below the specified diameter, this would have a small affect on overall stresses. However, a small change in diameter of the valve stem significantly changes the amount of clearance between the exhaust valve stem and the exhaust valve guide. Excessive clearance can lead to exhaust valve sticking, which can lead to overstress fracture. The engine total time was 2,079 hours, and it had not been overhauled since it was new in 1975. The manufacturer recommended overhaul at 2,000 hours or after 12 years of service life. Given the high hours on this engine and the number of years since overhaul, it was likely that the failure was due to exhaust valve sticking.
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
Flight instructor
- Certificate: flight instructor, commercial pilot
- Ratings: multi-engine land; single-engine land; instructor: airplane multi-engine; instructor: airplane single-engine; instructor: instrument airplane; instrument: airplane
- Flight time: 3,542 hours in all
- Medical certificate: Class 2 (valid medical--w/ waivers/lim.)
- Seat: rgt
- Injury: fatal
Dual student
- Flight time: 225 hours in all
- Medical certificate: None
- Seat: left
- Injury: fatal
The aircraft
- Airframe total time: 2,097 hours
- Last inspection: annual inspection, April 6, 2001; 118 hours since
- Maximum gross weight: 2,450 lb
- Seats: 4
- Landing gear: fixed
- Engine: Lycoming O-360-A4K (piston); 0 hours total
The flight
- Departed from: L52 San Luis Obispo CA at 11:30 pm
- Destination: 3O8 Harris Ranch CA
- Flight plan: none
- A second pilot was aboard
Weather at the time
- Light: daylight
- Wind: at 4 knots
- Visibility: 10 statute miles
- Sky: clear
- Temperature: 54°F (12°C), dew point 39°F (4°C)
- Altimeter: 30.01 inHg
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Crew | 2 | |||
| Passengers | 1 | 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.
About this page
Everything above comes from the NTSB's public accident database: the narrative, probable cause and findings are the NTSB's own words, and the coded tables behind its report (pilot, aircraft, flight, weather, injuries, sequence of events) are written out in plain English. Pilots' ages, home towns and medical details are left out on purpose. The documents and photographs are the NTSB's docket, the folder of records gathered during the investigation, shown as the NTSB released them (the NTSB redacts some personal details first) and listed under the NTSB's own titles. This site's own text never names pilots, passengers or anyone else involved. A preliminary report describes what is known soon after the event and can change; the final report, with the probable cause, usually follows one to two years later and this page is refreshed when it does. Case number LAX02FA148.