Accident Beechcraft N35 N7HB,
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ASN Wikibase Occurrence # 356334
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Date:Thursday 9 January 1997
Time:15:05 LT
Type:Silhouette image of generic BE35 model; specific model in this crash may look slightly different    
Beechcraft N35
Registration: N7HB
MSN: D-6750
Total airframe hrs:3883 hours
Engine model:Continental IO-470
Fatalities:Fatalities: 0 / Occupants: 3
Aircraft damage: Substantial
Location:Holbrook, AZ -   United States of America
Phase: Take off
Departure airport:(P14)
Destination airport:Flagstaff, AZ (KFLG)
Investigating agency: NTSB
Confidence Rating: Accident investigation report completed and information captured
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.

Probable Cause: 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.

Accident investigation:
Investigating agency: NTSB
Report number: LAX97LA084
Status: Investigation completed
Duration: 1 year and 4 months
Download report: Final report




Revision history:

12-Mar-2024 21:30 ASN Update Bot Added

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