NTSB Factual Report

HISTORY OF FLIGHT

On October 26, 2014, about 1100 Pacific daylight time, a Cessna 172S, N353MV, experienced a propeller blade separation during the departure roll at Santa Monica Municipal Airport, Santa Monica, California. Justice Aviation, Inc., was operating the airplane under the provisions of 14 Code of Federal Regulations (CFR) Part 91. The flight instructor, the pilot-undergoing-instruction, and the passenger were not injured; the airplane sustained substantial damage. The local instructional flight was departing at the time of the accident. Visual meteorological conditions prevailed and no flight plan was filed.

The flight instructor stated that after completing a normal run-up, the airplane was cleared for takeoff on runway 21. Upon applying full throttle, he heard a loud "bang" which was followed by a violent vibration. He retarded the throttle back to idle and the engine stopped producing power. After egressing the airplane he realized that half of a propeller blade was missing. As a result of the vibration, the airplane incurred damage to the firewall.

AIRPLANE INFORMATION

The airplane was a Cessna 172S, serial number (s/n) 172S9908, manufactured in 2005. The airplane was equipped with a McCauley fixed pitch aluminum propeller, model number 1A170E/JHA7660 (s/n ZB23071), which had amassed a total time in service of about 3,590 hours. A review of the maintenance records revealed that the propeller had undergone a 100-hour inspection on September 23, 2014, at which time it had accumulated a total time in service of about 3,544 hours and 2,587 hours since last overhaul (conducted in July 2008).

The propeller was subject to McCauley's Service Bulletin SB240E which addressed additional inspection requirements due to cracks and surface discontinuities between the 6 and 24 inch stations, the failure area of the accident blade. The maintenance records indicated that the service bulletin was complied with during the July 2008 overhaul at an estimated total propeller time of about 960 hours.

SB240E required additional inspection requirements for the propellers installed on aircraft operating as flight schools, such as the operator of the accident airplane. It stated that those aircraft must be inspected in accordance with the service bulletin every 1,000 hours or 72 calendar months (whichever occurs first). There were no maintenance records that indicated the SB240E was complied with since July 2008. At the time of the accident, the propeller had amassed 2,630 hours since SB240E was last complied with, equating to the propeller being about 1,630 hours out of compliance.

Additionally, there were no records that indicated a 2,000 hour or 72 calendar month TBO (time between overhaul) of the propeller was complied with as mandated in McCauley's propeller information manual. At the time of the accident the propeller was about 630 hours past TBO.

The log book entries indicated that the propeller was dressed and painted shortly after the overhaul during a 100-hour inspection in June 2009 at a total time of 981 hours. The owner/operator information manual notes that the entire propeller should be checked for corrosion, cracks and other damage at each 100 hour and annual inspections.

TESTS AND RESEARCH

The propeller was examined at the National Transportation Safety Board (NTSB) Materials Laboratory. The complete examination report with pictures is located in the public docket for this accident. Examination revealed that one blade of the fixed pitch propeller had a chordwise fracture that was 11.63 inches outboard from the centerline of the hub, as measured at the leading edge of the airfoil section. The section of propeller blade that was released during the accident was not found/recovered.

There was blistered paint on both the flat and camber faces of both the fractured and intact blades. Probing the paint blisters revealed underlying white powder material and shallow pits consistent with pitting corrosion in aluminum alloys. However, no pitting was visible in the fatigue origin area. The surface of the blade showed a yellowish coloration consistent with Alodine (chromate conversion coating for aluminum alloys). For distance aft of the leading edge, that yellow coloration appeared to have been abrasively removed and there was evidence of widespread corrosion pitting.

Optical examination of the fracture faces revealed shiny faceted markings consistent with fatigue progression in aluminum alloys. Beach marks and fracture traces indicated fatigue initiation on the flat face of the blade about 0.2 inch aft of the leading edge of the airfoil. From the origin the fatigue propagated through an estimated 60-percent of the total airfoil cross section before final overstress fracture.

High magnification optical examinations revealed a single fatigue origin initiating sub-surface on flat faceted region of the fractured propeller blade. The faceted region was inclined about 45 degrees to the fatigue plane and intersected the flat face of the blade at a similar angle. The single origin was approximately 0.010 inch below the flat face of the blade and about 0.2 inch aft of the leading edge.

NTSB Probable Cause

The separation of a section of a propeller blade due to fatigue cracking. Contributing to the accident was the operator’s failure to comply with the manufacturer’s maintenance and inspection instructions.