"Ron Lee" wrote in message
...
If you are flying who cares? Unless you are in a sandstorm or
volcanic ash downfall area my ASSUMPTION is that unfiltered air in
flight is not a hazard for the engine.

Most of the time, that's true. However, I wouldn't limit the conditions to
rare events like "sandstorm or volcanic ash". I have flown through
significant dust plumes, cause by nothing other than winds aloft carrying
dirt from terrain. One time, I could see the plume stretch all the way from
Mt St Helens out to the coast, some 100 miles away.

Clearly this sort of condition isn't nearly as harmful as the more dense
events, like a sandstorm or volcanic ash. But still, I was happy to have my
engine breathing filtered air when I went through it, and this sort of thing
is quite a bit more common than the more dense events.

Pete