The current entry noting that the crash resulted in the loss of all crew is incorrect. My grandfather (David H Thimmes) was the armorer/gunner on that ship.  
As the story goes, one or several engines were all shot up or flak damaged on a mission but the ship eventually made it back to base.  base. At some point the engines were replaced and it was required that they be tested at altitude.  
Again, the story was that when reported, grandpa had “forgotten” his electric suit and the entire gunnery crew was exempted from the test flight. I have the names and pics of all crewmembers and their positions. 
From what I read it was never determined what happened on the test flight, only that the aircraft exited the clouds in a nosedive and crashed into the ground killing the flight crew. 

LTCFlynn