# NTSB LAX91LA157: Cessna 172N, N733MQ, Stockton, CA, April 5, 1991

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Limited investigation · Final report
- Date: April 4, 1991, 19:40 local (Apr 5, 1991, 03:40 UTC)
- Place: Stockton, CA
- Location: 37.9577° N, 121.2908° W: Placed by OpenAirDocs: center of Stockton, CA, within about 6 miles (OpenAirDocs)
- Nearby events: https://openairdocs.org/map.md?lat=37.9577&lon=-121.2908&mi=10
- Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 2 uninjured
- Status: Completed, report May 3, 1993
- Report: Approved by Office Director
- NTSB case key (mKey): 27158
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX91LA157
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/27158/pdf
- Page: https://openairdocs.org/ntsb/LAX91LA157

## Probable cause

THE INSTALLATION BY MAINTENANCE PERSONNEL OF AN INCORRECT GASKET THAT RESULTED IN THE LOSS OF THE ENGINE MAGNETO.

## Sequence of events

In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf).

- Loss of engine power(total) - mech failure/malf, maneuvering - holding(ifr)
  - ignition system,magneto - loss,total (cause)
  - maintenance,installation - improper, company maintenance personnel (cause)
- Forced landing, descent - emergency
- On ground/water encounter with terrain/water, landing - roll
  - terrain condition - soft (contributing factor)
- Nose over, landing - roll

## Analysis

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.

## Aircraft

- Registration: [N733MQ](https://openairdocs.org/deregistered/N733MQ-2013-05-07), registration cancelled 2013-05-07, S/N 17268400, built 1976 (OpenAirDocs)
- Reported make and model: CESSNA 172N
- Registry model: [Cessna 172N](https://openairdocs.org/model/cessna-172n) (registry code 2072434) (OpenAirDocs)
- Registry engine: [Lycoming 0-320 series](https://openairdocs.org/engine/lycoming-0-320-series) (registry code 41508, reciprocating) (OpenAirDocs)
- Category: Airplane
- Serial number: 17268400
- Airframe hours: 5600
- Engines: LYCOMING O-320-H2AD 160 horsepower reciprocating
- Damage: Substantial damage
- Flight: Instructional, Part 91
- Operator: West Valley Flying Club Inc.
- Registered owner: Ken Gottfredson
- Airworthiness certificate: Standard, Normal
- Last inspection: Annual, September 14, 1990, 230 hours before
- Departed: PAO, PALO ALTO, CA
- Destination: SCK, STOCKTON, CA
- Flight plan: IFR

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 27; commercial, flight instructor; airplane ratings: single-engine sea, multi-engine land, single-engine land, multi-engine sea; instrument ratings: airplane; medical: class 1, valid medical--w/ waivers/lim; seat: right; flight hours: 7,000 total, 300 in this make and model, 6,950 as pilot in command, 400 in the last 90 days, 100 in the last 30 days, 7 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Night/dark
- Wind: 270° at 8 knots
- Visibility: 30 statute miles
- Lowest ceiling: none
- Temperature: 64 °F, dew point 45 °F
- Altimeter: 30.00 inHg
- Observed at: SCK, 6 nm away

## FAA reports on this event (1)

The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs).

- [Accident 19910404009099A](https://openairdocs.org/incident/19910404009099A), Apr 4, 1991: Cessna 172N, Stockton, CA, Substantial damage. Engine quit on night training flight. Nosed over landing. Dual single shaft mag fell off engine, wrong gasket used.

From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model.

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