ASN Wikibase Occurrence # 365734
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| Date: | Friday 1 February 1991 |
| Time: | 13:30 LT |
| Type: |  Lancair 235 |
| Owner/operator: | Private |
| Registration: | N17S |
| MSN: | OJ-1988 |
| Engine model: | LYCOMING O-320 |
| Fatalities: | Fatalities: 0 / Occupants: 2 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | Agua Caliente, CA -
 United States of America
|
| Phase: | En route |
| Nature: | Private |
| Departure airport: | San Diego, CA (KMYF) |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
THE AIRCRAFT WAS ON CLIMB OUT WHEN A LOUD BANG WAS HEARD, FOLLOWED BY AN ENGINE OVERSPEED THEN ENGINE STOPPAGE. AFTER THE FORCED LANDING, THE PILOTS FOUND THAT BOTH WOODEN PROPELLER BLADES HAD SEPARATED FROM THE STEEL HUB ASSEMBLY. THE PROPELLER HUB WAS REMOVED FROM THE ENGINE AND SENT TO THE MANUFACTURER FOR FUNCTIONAL ANALYSIS AND DISASSEMBLY UNDER THE SUPERVISION OF FAA INSPECTORS. THE MANUFACTURER STATED THAT ALL INTERNAL COMPONENTS WERE FUNCTIONAL, HOWEVER, THE CAM ADJUSTMENT FOR THE HIGH AND LOW PITCH STOP SETTINGS HAD BEEN ALTERED FROM THE FACTORY SETTINGS. THE BLADE BUTT ENDS RETAINED IN THE HUB WERE REMOVED AND SUBMITTED TO THE FOREST PRODUCTS LABORATORY OF THE US DEPARTMENT OF AGRICULTURE FOR ANALYSIS. ACCORDING TO THE LABORATORY THE WOODEN BLADES FRACTURED AND SEPARATED DUE TO A HYDROLYSIS INTERACTION BETWEEN THE WOOD AND THE ADHESIVE CAUSED BY EXCESS MOISTURE AND HEAT. THE HYDROLYSIS IS A CHEMICAL DECOMPOSITION PROCESS OF THE WOOD AND GLUE RELATIONSHIP.
Probable Cause: THE FAILURE OF THE PROPELLER BLADES DUE TO A WEAKENING OF THE WOOD STRUCTURE DUE TO ACID HYDROLYSIS. A FACTOR IN THE ACCIDENT WAS THE INADEQUATE MAINTENANCE OF THE PROPELLER ASSEMBLY BY ALLOWING EXPOSURE TO EXCESSIVE MOISTURE AND HEAT.
Accident investigation:
 |
|
Sources:
NTSB LAX91LA090
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 20-Mar-2024 13:14 | ASN Update Bot | Added |
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