My only fatality was from blunt force trauma to the head when his head slammed into the panel. Had his waist belt on but not the shoulder strap (3 point seatbelt). Had he had the shoulder strap he probably would have lived with cuts and bruises.
Then again he would probably have made the runway had he just declared emergency instead of being all vague. And he wouldn’t have had an emergency at all if he hadn’t run out of gas 50 miles before his destination.
A 3 point is useless when it’s not properly engineered for the airframe it’s bolted to. It’s not like they have done 50 years of crash testing daily like they do in the automotive industry.
The helmet is really your best bet. For me and friends who grew up on off-road motorcycles and trucks it’s SOP.
The problem is wearing one with passengers who don’t have one.