Daytime VFR flight legality depends on FAR 91.205, requiring specific functioning instruments (air speed indicator, altimeter, compass, etc.). A helpful mnemonic is "A TOMATO FLAMES" to remember them.
Pilots might be able to breathe during a smoke emergency, but landing is a problem if pilots can't see their instruments.
Diesel aircraft engines promise lower fuel burn and cheaper operating costs at a time when every gallon and every kilogram ...