A. A. Johnson, Metals Research Inc., Louisville, KY; R. J. Storey, University of Louisville, Louisville, KY
On September 25th, 1999, a Piper PA-22-150 light aircraft crashed and caught fire in Goshen, Kentucky. Both of the occupants were killed. An investigation by the National Transportation Safety Board did not reveal a cause for the crash. Their report noted that about 8 inches was missing from one propeller tip, and that the missing piece was not recovered from the accident site.
Examination of the fractured propeller revealed extensive grain boundary separation in the vicinity of the fracture. Chemical analysis showed that the propeller had been manufactured from an Al-3.54Cu-0.77Mg-0.73Si-0.26Fe alloy. In a scanning electron microscope the fracture surface exhibited grain corners and edges both heavily rounded by corrosion. EDAX traces revealed the presence of fluorine in the vicinity of the fracture.
It was concluded that the integrity of the propeller had been impaired by a corrosive fluorine-containing material which had come into contact with it. This was perhaps a cleaning solution containing hydrogen fluoride. Litigation followed the accident but the case was recently settled without a ruling by the court.
A light aircraft crashed killing the pilot and passenger. Several inches were found to be missing from one tip of its propeller which was found to have failed by severe intergranular corrosion. Fluorine was found in the vicinity of the fracture and on the fracture surface.
