Cessna 172N accident near Stockton, California, April 5, 1991
On April 5, 1991 at about 3:40 am local time, a Cessna 172N, registered N733MQ, was substantially damaged in an accident near Stockton, California. It was an instructional flight under general aviation rules (Part 91). No one was hurt; 2 people were on board or involved. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
THE INSTALLATION BY MAINTENANCE PERSONNEL OF AN INCORRECT GASKET THAT RESULTED IN THE LOSS OF THE ENGINE MAGNETO.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- April 5, 1991 · about 3:40 am local time
- Place
- Stockton, California
- Type
- Accident
- Injuries
- No one was hurt; 2 people were on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Cessna 172N · all 172Ns on the register
- Registration
- N733MQ · no longer on the register · serial 17268400
- Damage
- Substantial damage
- Flight
- Instructional flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
THE CERTIFICATED COMMERCIAL PILOT/CERTIFIED FLIGHT INSTRUCTOR AND A CERTIFICATED PRIVATE PILOT/INSTRUMENT STUDENT WERE IN A HOLDING PATTERN, IN VFR CONDITIONS, WHILE ON AN INSTRUMENT TRAINING FLIGHT WHEN THE ENGINE QUIT. THE CFI MADE A FORCED LANDING IN AN OPEN FIELD. DURING THE LANDING ROLL, THE AIRPLANE ENCOUNTERED SOFT TERRAIN AND NOSED OVER. EXAMINATION OF THE ENGINE REVEALED THAT THE MAGNETO ASSEMBLY FELL OFF THE ENGINE. AN IMPROPER GASKET WAS INSTALLED UNDER THE MAGNETO HOUSING THAT PREVENTED THE MAGNETO FROM BEING PROPERLY TIGHTENED TO THE REQUIRED TORQUE SETTING. GASKET MATERIAL UNDER THE NUT PROVIDED A CUSHION AFFECT THAT ALLOWED THE NUT TO VIBRATE LOOSE.
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: flight instructor, commercial pilot
- Ratings: multi-engine land; multi-engine sea; single-engine land; single-engine sea; instructor: airplane multi-engine; instructor: airplane single-engine; instrument: airplane; rotorcraft: glider
- Flight time: 7,000 hours in all; 300 in this make and model; 400 in the last 90 days; 100 in the last 30 days; 6,950 as pilot in command; 5,000 on instruments
- Medical certificate: Class 1 (valid medical--w/ waivers/lim.)
- Seat: rgt
The aircraft
- Airframe total time: 5,600 hours
- Last inspection: annual inspection, September 14, 1990; 230 hours since
- Maximum gross weight: 2,300 lb
- Seats: 4
- Landing gear: fixed
- Engine: Lycoming O-320-H2AD (piston); 0 hours total
- Operator: West Valley Flying Club INC.
The flight
- Departed from: PAO Palo Alto CA at 2:50 am
- Destination: SCK Stockton CA
- Flight plan: IFR
- Runway 0
- A second pilot was aboard
Weather at the time
- Light: night, dark
- Wind: from 270° at 8 knots
- Visibility: 30 statute miles
- Sky: scat at 25,000 ft
- Temperature: 64°F (18°C), dew point 45°F (7°C)
- Altimeter: 30.00 inHg
- Observation at 3:35 am from SCK, 6 miles away
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Crew | 2 |
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.