What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
(.4)The airplane experienced an inflight loss of its propeller assembly. A witness observed the airplane spiraling downward similar to that of a flat spin with smoke coming from it. Examination of the fractured propeller mounting flange revealed a separation of the propeller mounting flange from the remainder of the crankshaft which was the result of fatigue cracking that initiated between the lightening holes in the flange. There is an airworthiness directive and service bulletin that specifically addressed the subject engine when it is installed on the Piper PA-30 airplane. These inspection requirements arose because of cracking problems generated by bending of the mounting flange under certain aerobatic-type maneuvers, primarily maneuvers that add stresses from gyroscopic action. The weight and balance after the loss of the propeller was 1,531 pounds at 70.09 inches aft. The center of gravity envelope for the N320L is between 60.75 to 66.75 inches aft. (-23) aircraft departed oshkosh Wisconsin wittman airport for chicago area (aurora). Witnesses heard engine popping sounds, other witness saw aircraft spiraling down trailing smoke. Aircraft crashed in soybean field, 30 degre es nose down, 9 degrees left wing low. Aircraft missing prop spinner, propeller and starter ring gear.
As the FAA filed it
(.4)THE AIRPLANE EXPERIENCED AN INFLIGHT LOSS OF ITS PROPELLER ASSEMBLY. A WITNESS OBSERVED THE AIRPLANE SPIRALING DOWNWARD SIMILAR TO THAT OF A FLAT SPIN WITH SMOKE COMING FROM IT. EXAMINATION OF THE FRACTURED PROPELLER MOUNTING FLANGE REVEALED A SEPARATION OF THE PROPELLER MOUNTING FLANGE FROM THE REMAINDER OF THE CRANKSHAFT WHICH WAS THE RESULT OF FATIGUE CRACKING THAT INITIATED BETWEEN THE LIGHTENING HOLES IN THE FLANGE. THERE IS AN AIRWORTHINESS DIRECTIVE AND SERVICE BULLETIN THAT SPECIFICALLY ADDRESSED THE SUBJECT ENGINE WHEN IT IS INSTALLED ON THE PIPER PA-30 AIRPLANE. THESE INSPECTION REQUIREMENTS AROSE BECAUSE OF CRACKING PROBLEMS GENERATED BY BENDING OF THE MOUNTING FLANGE UNDER CERTAIN AEROBATIC-TYPE MANEUVERS, PRIMARILY MANEUVERS THAT ADD STRESSES FROM GYROSCOPIC ACTION. THE WEIGHT AND BALANCE AFTER THE LOSS OF THE PROPELLER WAS 1,531 POUNDS AT 70.09 INCHES AFT. THE CENTER OF GRAVITY ENVELOPE FOR THE N320L IS BETWEEN 60.75 TO 66.75 INCHES AFT. (-23) AIRCRAFT DEPARTED OSHKOSH WISCONSIN WITTMAN AIRPORT FOR CHICAGO AREA (AURORA). WITNESSES HEARD ENGINE POPPING SOUNDS, OTHER WITNESS SAW AIRCRAFT SPIRALING DOWN TRAILING SMOKE. AIRCRAFT CRASHED IN SOYBEAN FIELD, 30 DEGRE ES NOSE DOWN, 9 DEGREES LEFT WING LOW. AIRCRAFT MISSING PROP SPINNER, PROPELLER AND STARTER RING GEAR.
NTSB investigation
The NTSB’s investigation of this event, with its probable cause and findings. Matched to this report by N-number and date.