Accident Details
On January 5, 2009, at approximately 1115 eastern standard time, a Grumman AA-5B Tiger, registration N28862, sustained substantial damage following an in-flight separation of a propeller blade and a subsequent forced landing near Milford, Indiana. The aircraft was conducting an instructional flight under 14 Code of Federal Regulations Part 91 without a flight plan. Visual meteorological conditions prevailed. The private pilot and flight instructor were not injured. The local flight had departed at about 1045.
The private pilot reported that the airplane was in cruise flight at 3,500 feet mean sea level when a loud bang was heard, followed by violent vibration. He secured the engine and raised the nose to stop the propeller's rotation, then executed a forced landing to an open field.
Post-Accident Examination
A post-accident examination revealed that a 20-inch length of one blade had separated from the two-bladed, fixed-pitch propeller. The separated section was not recovered. Secondary damage was observed to the engine assembly, engine mounts, and firewall.
Metallurgical examination of the remaining blade portion showed a chordwise fracture approximately 18 inches from the hub centerline (20 inches from the tip). The fracture surface exhibited features consistent with fatigue failure covering about 70 percent of the area, with the remaining area consistent with overload failure. Fatigue striations originated from an area of corrosion on the cambered side of the blade. Visual inspection using low-powered magnification revealed corrosion pitting distributed over the entire cambered surface.
Maintenance History
Maintenance records indicated the propeller was installed new on the accident airplane in September 1983 and was reconditioned in May 1987. The most recent annual inspection was completed on October 31, 2008. At the time of the accident, the propeller had accumulated 2,326 hours total time in service, with 8 hours since the annual inspection.
Airworthiness Directive (AD) 69-09-03 R3, effective May 15, 1996, required factory inspection and reconditioning for propellers with 500 hours or more of flight time. Propellers inspected or reworked per that AD were to be identified with the suffix letter "K" after the serial number. The accident propeller included a "K" suffix, consistent with compliance. No subsequent ADs related to the accident propeller had been issued.
The manufacturer issued Service Bulletin R-15A on October 4, 1989, recommending inspection and repair procedures for corrosion issues. It stated that propeller blades should be inspected for corrosion during annual or 100-hour inspections, with any corrosion repaired or the propeller reconditioned depending on extent and severity. Service Bulletin R-17, issued March 16, 1999, noted FAA approval for increasing the time between overhaul/reconditioning cycles (TBO) from 1,000 hours to 2,000 hours for normal and utility operations, provided the propeller had not sustained damage needing immediate attention. However, regulations do not require compliance with TBO limits for non-commercial operations; continued airworthiness is based on the propeller's condition.
FAA Advisory Circular (AC) 20-37E states that a detailed inspection should be completed at each annual inspection or as required by aircraft maintenance procedures, including visual examination of propeller blades using 10-power magnification for questionable areas, looking for excessive wear, erosion, damage, nicks, cracks, corrosion, lightning strike, or ground strike.