The airplane pilot couldn't see Julie/Miyax because of the fog. What did she learn from the sound of the plane?

Julie learns many things from the sound of the plane in Part 3 of Julie of the Wolves.  First, because Julie is adventuring in a mostly untraveled area of Alaska, Julie knows that this must be a plane carrying hunters. Next, Julie learns that shots will only ring out from the plane when the plane flies low enough.  The hunters must be able to see well enough to get a good shot.  Further, they must be close enough for their shot to make an effective kill.  Finally, Julie learns to recognize the sound of the plane turning around to "make another pass."  This involves the plane engine sound becoming more faint and then getting louder again.  

The sound of the plane is important to the story because it involves the tragedy of Julie losing Amaroq, the great wolf.  Julie hides in a barrel and watches as the hunters pursue both Amaroq and Kapu.  Even though Amaroq tries to avoid the bullets (emitted from the low-flying plane) by veering from side to side, he is eventually killed.  Kapu is wounded and is only saved by approaching Julie hiding in the barrel.  The plane is flying so low that Julie can hear the hunters laughing at their kill.  Julie cries out in desperate helplessness.