[smcl]

It's just a misunderstanding I think. It sounds like the OP's dad was in the RAF during the war, and "risking his life to protect the farmer" was a reference to that rather than the particular flight he was on when he had to make the emergency landing in the field.

So I can sort-of understand why they are being defensive. In their eyes there are commenters denying their father's effort in the war. But the commenters were actually either trying to understand if there's an extra story or were puzzled what kind of life-saving flights could be conducted in the British mainland in the years following the war.