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.
An Alternative Theory
Using ‘Memory Map’ software to show the hillside in ‘3d’ it is easy to see how the
crew may have thought they were flying along the coast when they were actually in
a blind valley with no way out.