CHERRY POINT, NC, USA
N78321
Globe GC1B
A Globe GC1B lost a propeller blade in-flight while maneuvering in the number two position of a formation of three airplanes, a propeller blade separated from the propeller hub assembly. The second propeller blade, along with the hub assembly, subsequently separated from the engine crankshaft. Examination of the recovered propeller hub fracture faces disclosed fatigue cracking. The fatigue fracture propagated until it intersected the outside hub surface. According to McCauley Propeller the fatigue fracture reduced the propeller hub load carrying capacity until it was no longer a sufficient cross section to carry the centrifugal load of the propeller.
On April 1, 2001, at 1400 eastern daylight time, a Globe GC1B, N78321, registered to a private owner, lost a propeller blade in-flight while maneuvering at an air show in Cherry Point, North Carolina. The formation flight was operated by the pilot under the provisions of Title 14 CFR Part 91 with no flight plan filed. Visual weather conditions prevailed at the time of the accident. The commercial pilot was not injured, and the airplane sustained substantial damage. The flight departed Cherry Point, North Carolina, at 1350. According to the pilot, while maneuvering in the number two position of a formation of three airplanes, a propeller blade separated from the propeller hub assembly. The second propeller blade, along with the hub assembly, subsequently separated from the engine crankshaft. The second propeller blade was subsequently recovered for examination. Examination of the airplane revealed a catastrophic engine failure as a result of a propeller blade separation. Examination also revealed part of the crankshaft was sheared at the hub attachment, and numerous engine attachment bolts were sheared. The propeller assembly examination revealed a hub facture that originated in the root of the second inboard retention thread of the No. 2 socket. The facture was aligned along the trail edge side of the hub. Examination of the fracture faces revealed features consistent with fatigue cracking. The fatigue fracture propagated until it intersected the outside hub surface. According to McCauley Propeller the fatigue fracture reduced the propeller hub load carrying capacity until it was no longer a sufficient cross section to carry the centrifugal load of the propeller. The propeller examination also revealed that it had been modified for oil-fill crack detection, in accordance with McCauley Propeller, service bulletin 182, dated July 16, 1990. However, there was no evidence of the red oil found inside the hub or on any pitch change components. No oil film was present on any of the components. The retention bearing races were rusted and brinnelled consistent with the absence of lubrication while the propeller had been in operation. The condition of the components suggests that the propeller had been drained of its red oil. A review of the aircraft records showed that the airplane was modified with a Meryln Product Supplemental Type Certificate (STC), P3EA that included the installation of a McCauley model D2A34C67-NP/76C-2 propeller. Reportedly, McCauley Propeller did not approve or seek the Federal Aviation Administration (FAA) approval of a specific airframe/engine/propeller installation of the D2A34C67 propeller on the Globe GC-1B aircraft. Note #9 of Type Certificate data sheet No. P3EA, list certain propeller engine combinations that are approved vibration wise for use on "Normal Category Single-Engine Tractor Aircraft". According to Merlyn Products and McCauley Propeller System, the accident propeller hub assembly was not approved for aerobatics flight. Reportedly, aerobatic usage of the accident type propeller hub assembly can increase the propeller operating stresses beyond the approved allowable limits. According to the pilot/owner, N78321 was not used for aerobatic flight. Meryln Products reported that the D2A34C67 propeller hub assembly is no longer available as part of STC P3EA.
Fatigue cracking of the propeller hub that resulted in the in-flight separation of a propeller blade.
Source: NTSB Aviation Accident Database
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