CHI93LA365

The pilot departed for a local pleasure flight, and was about 5 miles south of the departure airport when there was a loud pop and the airplane began to '...vibrate violently.' The pilot stated the vibration became manageable when he reduced engine power to idle. He reported the engine lost power completely as the airplane glided toward the selected forced landing site. The airplane landed hard and flipped over during the landing roll, coming to rest inverted. Postaccident investigation revealed the outboard 13.75 inches of one propeller blade separated during flight. The separated portion was recovered, and both pieces of the failed blade were examined by the ntsb's materials lab. The lab's examination revealed the crack arrest positions emanated from a cavity on the flat face of the propeller blade. The propeller was checked for balance, blade track and angle, and was painted 9 1/2 months before the accident. The cavity contained paint similar to the rest of the flat face of the blade.

On September 18, 1993, at 1030 hours central daylight time, a Grumman AA5B, N55VL, operated by a private pilot on a local pleasure flight, experienced severe vibrations after a propeller blade tip separated during cruise flight. The airplane sustained substantial damage during a subsequent forced landing in Aurora, Illinois. The pilot, the sole occupant, reported no injuries. Visual meteorological conditions prevailed for the flight, no flight plan was filed. The flight operated under 14 CFR Part 91, and originated from West Chicago, Illinois at 1010 hours.

The pilot stated he took off on Runway 28 at DuPage County Airport (DPA) in West Chicago, for a local pleasure flight. He reported he was about 5 miles south, climbing through 2,300 feet Mean Sea Level (MSL), when "...there was a loud pop and plane began to vibrate violently...lowered nose and reduced power to idle...still vibrating but manageable." The pilot stated as he glided eastbound toward an "...open, unpopulated space..." the "...engine quit." The airplane touched down hard and flipped over during the forced landing, coming to rest inverted.

Postaccident investigation revealed the outboard 13.75 inches of one propeller blade had separated in flight. The separated portion of propeller blade was recovered. The two portions of the failed propeller blade were sent to the Materials Laboratory Division of the NTSB's Office of Research and Engineering.

Metallurgical examination of the fracture surfaces indicated about 60% of the blade cross section failed on a flat, chordwise plane, and contained crack arrest positions, typical of fatigue failure. The crack arrest positions emanated from a cavity on the flat face of the propeller blade. The remaining 40% of the fracture surface failed on a 45 degree shear plane and was matte in appearance, typical of overstress failure. A copy of the Metallurigist's factual report is appended.

Examination of propeller maintenance records revealed the propeller had been cleaned and balanced on an annual basis, in conjunction with the aircraft Annual Inspection. The most recent aircraft Annual Inspection occurred November 28, 1992. Records indicate the propeller was signed off for balance, blade angle and track on December 2, 1992. The Record of Repair indicated the propeller blades were reworked, "Leading edges only." The propeller was painted before it was returned to service. The metallurgical factual report stated: "The cavity contained black paint that was similar in appearance to the black paint on the remainder of the flat face of the blade." Excerpts from the Sensenich Metal Propeller Repair Manual, Maintenance invoices, and the Propeller Logbook are appended.