A locomotive style whistle powered by bleed air?
Good idea! Something that creates a distinct sound is relevant.
One witness to the Royal Commission into the Feb 7th fires in Victoria stated that she heard what she thought was the sound of a helicopter but was in fact the sound of the approaching bushfire!
To elaborate the idea is to provide a bushfire warning well ahead of the fire front, lets say 10-20 kms, to give communities time to react.
mickjoebill