How long was Brian's plane in the air before it crashed?

In Gary Paulson's young reader's book "Hatchet" a young boy, Brian Robeson, is flying to visit his father. He is in a single engine airplane.  The pilot suffers a massive heart attack above the Canadian wilderness and Brian is left alone to try and figure out how to fly the plane.  The plane lurches because of turbulence and starts to dive its nose downward.  Brian knows he has to do something.  He calls for help on the radio.  For a half an hour he keeps trying to get someone on the radio.  He is keeping the plane going but does not know what else to do.  Another hour passes and he is still in the air.  He repeated radio calls every 10 minutes 17 times.

170 + 60 + 30 = 4 hrs. and 33 minutes(He was in the air)