# NTSB ATL92LA063: Beech A36, Mt. Pleasant, TN, March 15, 1992

- Type: NTSB accident investigation
- Classification: Accident · Serious injuries · Limited investigation · Final report
- Date: March 15, 1992, 11:45 local (17:45 UTC)
- Place: Mt. Pleasant, TN
- Coordinates: 35.550575, -87.19065 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=35.5506&lon=-87.1907&mi=10
- Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping)
- Highest injury: Serious injuries
- Injuries: 1 serious, 3 minor
- Status: Completed, report June 30, 1993
- Report: Approved by Office Director
- NTSB case key (mKey): 8572
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ATL92LA063
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/8572/pdf
- Page: https://openairdocs.org/ntsb/ATL92LA063

## Probable cause

THE MANUFACTURER'S FAILURE TO PROVIDE ADEQUATE TORQUE INFORMATION WHICH RESULTED IN THE LOSS OF TORQUE ON THE CYLINDER HOLD DOWN NUTS AND THE COMPLETE LOSS OF ENGINE POWER.

## 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, cruise
  - engine assembly,cylinder - separation
  - engine assembly,cylinder - undertorqued (cause)
  - maintenance,overhaul - inadequate, manufacturer (cause)
  - procedure inadequate, manufacturer (cause)
- Forced landing, descent - emergency
- In flight collision with object, descent - emergency
  - object - tree(s)

## Analysis

WHILE CRUISING THE ENGINE DEVELOPED A VIBRATION AND STARTED RUNNING ROUGHLY. THE PILOT REDUCED POWER AND ESTABLISHED A TRACK FOR AN EMERGENCY LANDING TO A NEARBY COUNTY AIRPORT; THE AIRPLANE CRASHED ABOUT ONE MILE SHORT OF THE AIRPORT. EXAMINATION OF THE ENGINE ASSEMBLY DISCLOSED THAT A PIECE OF THE CRANKCASE WAS BROKEN ABOVE NUMBER 2 CYLINDER AND THE CYLINDER WAS PARTIALLY SECURED BY ONE HOLD DOWN NUT ON THE BOTTOM LEFT SIDE. FURTHER EXAMINATION REVEALED FRETTING BETWEEN THE CYLINDER FLANGE AND THE ENGINE CASE. ALL CRANKCASE FRACTURES SHOWED SIGNS OF OVERLOAD FAILURE. THE ENGINE MAINTENANCE LOGS DISCLOSED THAT THE ENGINE'S CRANKCASE HAD BEEN REPLACED ON 10/24/90; THIS ENGINE MALFUNCTION OCCURRED 258 HOURS LATER. SUBSEQUENT TO THIS ACCIDENT, CONTINENTAL MOTORS ISSUED A SERVICE BULLETIN WHICH INCREASED THE TORQUE VALUE FOR THE CYLINDER HOLD DOWN NUTS, AND INSTRUCTED THAT THE STANDARD SIX POINT HOLD DOWN NUTS BE REPLACED WITH TWELVE POINT NUTS DURING OVERHAUL.

## Aircraft

- Registration: N174OD (not matched to a registry record)
- Reported make and model: BEECH A36
- Category: Airplane
- Serial number: E1796
- Airframe hours: 3273
- Engines: CONTINENTAL IO-520-BB 285 horsepower reciprocating
- Damage: Substantial damage
- Flight: Personal, Part 91
- Operator: Snyder, Michael C.
- Registered owner: Snyder, Michael C.
- Airworthiness certificate: Standard, Normal
- Last inspection: Annual, January 7, 1992, 30 hours before
- Departed: HSV, HUNTSVILLE, AL
- Destination: SPI, SPRINGFIELD, IL
- Airport: MRC, Maury County, runway 5, 5,003 × 75 ft, asphalt

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 53; private; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 2, valid medical--w/ waivers/lim; seat: left; flight hours: 1,420 total, 87 in this make and model, 1,262 as pilot in command, 24 in the last 90 days, 9 in the last 30 days

## Weather

- Conditions: Visual (VMC), Day
- Wind: 10° at 15 knots
- Visibility: 15 statute miles
- Lowest ceiling: 4,500 ft overcast
- Temperature: 45 °F, dew point 21 °F
- Altimeter: 30.00 inHg
- Observed at: BNA, 35 nm away

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.

---
OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.