NTSB Identification: LAX97LA084.
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Accident occurred Thursday, January 09, 1997 in HOLBROOK, AZ
Probable Cause Approval Date: 05/21/1998
Aircraft: Beech N35, registration: N7HB
Injuries: 3 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

Moments after lift-off, the propeller separated, & the aircraft (acft) veered off the runway, contacted soft soil, & nosed over. Investigation revealed the propeller hub failed forward of the attachment flange, around the circumference of the hub. The pilot said he had performed a thorough preflight & run-up, & found no discrepancies. Metallurgical exam of the hub revealed crack arrest marks, typical of fatigue, emanating from the 4th thread root on the aft piece of the hub. The crack was estimated to be several inches long before failure occurred. Review of records disclosed that McCauley Service Bulletin 179A, McCauley Service Letter 1989-5, & Airworthiness Directive (AD) 89-26-08 had not been complied with during the previous 5 annual inspections. These referenced propellers which should have incorporated an oil-filled configuration with red dye that would become visible once a hub had begun to crack. The AD cited McCauley '2A36C23/84B-0' Constant Speed Propellers. Both McCauley & the FAA engineering directorate, which wrote the AD, reported the intent was to capture all 2A36C23 hubs regardless of blade models. The hub on the accident acft was a McCauley 2A36C23-P-E, with blade Models S-84B-0 installed (rather than blade Models 84B-0). Unanimous response from mechanics & IA's, who worked on the acft during the previous 5 annuals inspections, was that the AD was not applicable since the propeller was not a '2A36C23/84B-0' as stated in the AD.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

fatigue failure of the propeller hub, which resulted in separation of the propeller assembly and reduction of aircraft control. Also causal was: the resultant lack of compliance with Airworthiness Directive (AD) 89-26-08, due to ambiguous and unclear wording of the AD as issued by the FAA. Factors relating to the accident were: non-compliance with McCauley Service Bulletin 179A and McCauley Service Letter 1989-5, and an encounter with soft terrain during the aborted takeoff.

Full narrative available

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