History of Flight
On October 26, 2014, at about 1100 Pacific daylight time, a Cessna 172S (registration N353MV) operated by Justice Aviation, Inc., was conducting a local instructional flight from Santa Monica Municipal Airport, California. During the departure roll on runway 21, after the flight instructor applied full throttle, a loud bang was heard followed by violent vibrations. The instructor reduced throttle to idle, and the engine stopped producing power. After egressing, it was discovered that half of a propeller blade was missing. The airplane sustained substantial damage to the firewall. The flight instructor, pilot-under-instruction, and passenger were not injured. Visual meteorological conditions prevailed; no flight plan was filed.
Aircraft and Propeller Information
The airplane was a 2005 Cessna 172S, serial number 172S9908. It was equipped with a McCauley fixed-pitch aluminum propeller, model 1A170E/JHA7660, serial number ZB23071, which had accumulated about 3,590 hours total time in service. The propeller had last been overhauled in July 2008, after which it had accrued about 2,587 hours. A 100-hour inspection was performed on September 23, 2014, at a total time of about 3,544 hours.
The propeller was subject to McCauley Service Bulletin SB240E, which addressed additional inspection requirements for cracks and surface discontinuities between the 6-inch and 24-inch stations of the blade—the area where the failure occurred. Records indicated that SB240E was complied with during the July 2008 overhaul at an estimated propeller time of about 960 hours. For aircraft operating as flight schools, SB240E mandated inspections every 1,000 hours or 72 calendar months, whichever came first. No records showed compliance with SB240E after July 2008; at the accident, the propeller had accumulated 2,630 hours since last compliance, about 1,630 hours beyond the required interval. Additionally, no records indicated compliance with the 2,000-hour or 72-month time-between-overhaul (TBO) specified in McCauley's propeller information manual; the propeller was about 630 hours past TBO. Logbook entries noted that the propeller was dressed and painted in June 2009 at 981 hours total time. The owner/operator manual stated that the entire propeller should be checked for corrosion, cracks, and other damage at each 100-hour and annual inspection.
Examination Findings
The National Transportation Safety Board's Materials Laboratory examined the propeller. One blade exhibited a chordwise fracture 11.63 inches outboard from the hub centerline, measured at the leading edge. The separated blade segment was not recovered. Both the fractured and intact blades showed blistered paint on their flat and camber faces; probing revealed underlying white powder and shallow pits consistent with pitting corrosion in aluminum alloys. However, no pitting was visible in the fatigue origin area. The blade surface had a yellowish coloration consistent with Alodine, which appeared abrasively removed aft of the leading edge, with widespread corrosion pitting.
Optical examination of the fracture faces revealed shiny faceted markings consistent with fatigue progression. Beach marks and fracture traces indicated fatigue initiation on the flat face about 0.2 inch aft of the leading edge. The fatigue propagated through approximately 60 percent of the total airfoil cross section before final overstress fracture. High-magnification examination disclosed a single fatigue origin initiating subsurface on a flat faceted region, inclined about 45 degrees to the fatigue plane. The origin was about 0.010 inch below the flat face and 0.2 inch aft of the leading edge.
Probable Cause
The investigation report did not state a probable cause.