The totals of bombers and crews lost rarely differentiate between those due to enemy fire and those that occurred during takeoffs, landings and collisions while forming-up. Years ago, I was heavy into WW2 flight simulators and eventually gained the confidence to try piloting a B-17 on a bombing mission. ...yep......went down in flames while pancaking during my first "assembly". My uncle was a belly turret gunner on a B-17 with the 92nd BG and he'd once commented that the assembly stage of the mission, was often more nerve wracking than the bombing run itself. On larger strikes, there could be more than one assembly stage as bombers from several fields were combined at multiple locations along the route.