Old bug... Boston and A20G have this odd thing where if you sneeze at it from ANY ANGLE ANYWHERE it will explode. I hit the starboard engine 5 times with 7mm guns only, and it blew up. I shot one in the side of the rear fuselage, and it blew up.
I think the pilot bubble is too large. Wild guess. I dont' see how HTC could have missed this, so it's highly unlikely, but it SEEMS (effects-wise) that the entire plane is a pilot hit area, and any hit from any area kills you instantly.