If the crew were peering through misty plastic windows in rain, looking for a fog
    shrouded coast line, believing that they would have a clear view when they reached
    it -  and enough time to turn away, and if the aircraft crossed the coast where it
    was obscured because the cloud was much lower than anticipated, there might have
    been a fleeting glimpse of the left hand side of 'Coombe Bottom' .  This would have
    appeared in the right place at the right time, on dead reckoning, and would have
    looked exactly like the seaward facing slopes of St Boniface Down or even the edge
    of Sandown Bay.  
Being very slightly off track, but only by a matter of yards which would be well
    within the margin of error, they saw what they expected to see - the hills along
    the edge of the coast on their left.   They began to climb as they had planned and
    turned right to cross Sandown Bay, possibly intending to climb back to cruising altitude
    and head for the Portsmouth beacon to use an instrument approach - and flew directly
     into a hillside when they expected to see open water.