I don't agree with a number of posts dismissing HUD under smoke in cockpit conditions. The HUD equipped aircraft that I fly was tested with a smoke generator in the cockpit generating so much smoke that the test pilot could not see his hand in front of his face. He could still read the HUD.
I suspect that this possibly has something to do with the frequency of the light projected. The HUD projector is not like a normal projector. If you put a sheet of white paper onto the combiner at night there will be no image displayed on the sheet. I'm guessing that the light is not dispersed all that much by the smoke and still gets to the combiner.
I advise other pilots that the HUD will still provide a reliable source of reference provided oxygen and eye protection are properly worn. Seeing out the front is another issue.
If anyone has evidence to the contrary I would like to hear it before I find out the hard way!
