The plane with helicopter rescue was a PBY.
The PBY crash landed on a frozen lake, all survived.
Survivor flown out by 2x Norseman of which one also crashed!
Then the helicopter was flown in to air lift those survivors!
PBY crash
Also a Great story but apperently not related to Grandad Henderson.
Unless he changed squadrons
Cannot find much plane crashes around april- may 1945.
Did find that the last PBY - U-boat encounter was 2 May