ASN Wikibase Occurrence # 284968
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| Date: | Monday 30 April 2007 |
| Time: | 15:43 LT |
| Type: |  Beechcraft S35 |
| Owner/operator: | Marc Incorporated |
| Registration: | N8820M |
| MSN: | D-7331 |
| Year of manufacture: | 1964 |
| Total airframe hrs: | 5662 hours |
| Engine model: | Continental IO-520-BA3B |
| Fatalities: | Fatalities: 0 / Occupants: 1 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | Brookfield, Missouri -
 United States of America
|
| Phase: | Unknown |
| Nature: | Private |
| Departure airport: | Raymond, MS (M16) |
| Fort Dodge Airport, IA (FOD/KFOD) | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
he pilot reported that the engine was "operating normally" as he was flying at 6,500 feet mean sea level when the "engine blew up." He elected to execute a gear up forced landing to a corn field about two miles from the airport, but the airplane impacted a ditch during the emergency landing. The engine teardown inspection revealed a hole in the crankcase approximately 3 inches by 3 inches above the number 4 cylinder, which included the 11 and 1 o'clock deck studs. The number 4 cylinder had separated from the crankcase and the number 4 connecting rod was not attached to the number 4 crankshaft pin. The number 4 connecting rod and rod cap exhibited signatures that were consistent with an overload event that deformed and/or sheared the threads on the nuts and bolts. Cylinder number 4 deck stud nuts 6, 7, and 8 were reported missing from the engine at the accident scene, and subsequently found inside the engine cowling of the aircraft. Cylinder number 4 deck studs 6, 7, and 8 were securely attached to the engine crankcase and the threads were clean and undamaged. The 2 o'clock cylinder deck stud was fractured and missing. The remaining deck studs and thru-bolts all exhibited ductile fractures indicative of tensile overload. The other five cylinders' thru-bolt and deck stud break-away torque measurements were recorded for each thru-bolt and deck stud. The inspection revealed that numerous thru-bolts and studs had break-away torque values that did not comply with the manufacturer's limitations. The aircraft engine's logbook indicated that the engine received an annual maintenance inspection on February 16, 2005. The engine logbook entry stated, "Removed and overhauled all 6 cylinders. Installed new rings, ground valves, cleaned and gapped spark plugs." The tach time indicated 5380.5 hours at the time of the annual inspection. At the time of the accident, the tach time was 5,662.24 hours, 281.74 hours since the cylinders had been replaced.
Probable Cause: Improper maintenance by maintenance personnel by not properly torquing cylinder thru-bolts. The loose stud nuts which resulted in the separation of the cylinder and the crop and ditch were factors.
Accident investigation:
 |
|
Sources:
NTSB CHI07LA127
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 01-Oct-2022 15:56 | ASN Update Bot | Added |
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