Jim,

<<It seems unreasonable to me that anyone would ever have a Jet A contamination as low as 10%.>>

The actual scenario was this. 

The delivery truck, with 1,000 gal of Jet A still loaded, fills up with 8,000 gal of Avgas.  The 9,000 gal mixture is added to whatever was left in the storage tank at the FBO.  A week or two later the delivery truck returns with another 8,000 gal. of Avgas and adds it to tank at the FBO.  The starting concentration is about 11%.  The actual concentration gets diluted every time more Avgas is added and when the

blend is added to whatever is left in the aircraft fuel tank.  It took three weeks before the source of emerging engine troubles was traced to contaminated Avgas.

The engines that received close to 11%  almost came apart in flight, resulting in a few emergency landings.  I received something up to 5%.  My engine did not shed metal but still took a beating.  The bearings were smeared and the exhaust valve seats were blue.  Avoiding non-catastrophic engine damage will require a reliable method of detecting very low levels of contamination. 

Chris 

 

Chris Zavatson
N91CZ

L360std