Accident Piper PA-34-200 N56484,
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ASN Wikibase Occurrence # 135296
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Date:Saturday 11 January 2003
Type:Silhouette image of generic PA34 model; specific model in this crash may look slightly different    
Piper PA-34-200
Owner/operator:The Aero Club
Registration: N56484
MSN: 34-7350338
Year of manufacture:1973
Engine model:Lycoming LIO-360-C1E6
Fatalities:Fatalities: 0 / Occupants: 2
Aircraft damage: Destroyed
Location:Westlake Village, CA -   United States of America
Phase: Manoeuvring (airshow, firefighting, ag.ops.)
Departure airport:Van Nuys, CA (VNY)
Destination airport:
Investigating agency: NTSB
Confidence Rating: Accident investigation report completed and information captured
The airplane collided with ground obstacles during a forced landing when the pilots could not maintain altitude after one propeller blade and part of the propeller hub from the right engine separated in flight. The CFI and the student practiced two simulated engine-out maneuvers. The CFI was reaching for the mixture control for a third simulation when he heard a loud bang. The airplane yawed violently to the right and began to lose altitude. The CFI turned toward his home field, but was having difficulty maintaining altitude. He decided that he would not be able to make it to the airport, and would have to make an off field landing. He landed in the only clear spot that he could see, which was a cemetery. The airplane collided with monuments and a wood chip pile before coming to rest next to a mausoleum. The right propeller hub fractured and separated. Investigators did not recover one blade and the corresponding part of the hub. The hub fractured as a result of fatigue cracking emanating from one of the grease-fitting holes. The fatigue cracking originated in the area of the grease-fitting threads closest to the interior surface of the hub, at the intersection between the grease-fitting hole and the chamfer. No material or manufacturing defect was found that could be identified as the source of the fatigue cracking. The fatigue cracking originated just outside the thread remnants of the grease fitting hole that were plastically deformed during a chamfering process. The grease fitting was located in a region where the wall of the hub was approximately at its thinnest, and where there was a slight change in the profile along the axis of the propeller. These geometrical factors would have led to high stresses at the edges of the hole. Chamfers were retrofitted to the grease-fitting holes by the manufacturer at both the interior and exterior surfaces of the hub in response to fatigue fractures that occurred in three-bladed propellers. This accident was the first occurrence of fatigue emanating from a grease-fitting hole for a two-bladed propeller. The chamfering was apparently introduced in an effort to smooth the stress distribution around the grease-fitting holes. The chamfer at the interior surface should have removed the stress concentration associated with the change in wall profile, but would also have decreased the amount of material in the wall, leading to higher stresses overall. The stress concentration associated with the grease-fitting hole and the chamfer, coupled with the location in a position where the hub wall was very thin, were likely sufficient to initiate fatigue cracking in this case. In more recently manufactured hubs, the grease-fitting holes have been relocated to positions where the hub wall is much thicker.
Probable Cause: a fatigue crack in the propeller hub due to the inadequate design location of the grease fitting and the chamfering process.

Accident investigation:
Investigating agency: NTSB
Report number: LAX03FA065
Status: Investigation completed
Download report: Final report



History of this aircraft

Other occurrences involving this aircraft
24 June 1995 N56484 Aero Club 0 Avalon, CA sub


Revision history:

21-Dec-2016 19:26 ASN Update Bot Updated [Time, Damage, Category, Investigating agency]
08-Dec-2017 18:02 ASN Update Bot Updated [Other fatalities, Departure airport, Source, Narrative]
02-Jan-2022 07:41 SANMJN Updated [Location]

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