Originally Posted by
PHLGovFlyer
I think you're missing a key point in the overall discussion. Crash survivability depends on a large number of factors where small differences can matter greatly. For example, a small difference in lap belt position (low and tight against the pelvic bone versus higher on the abdomen) can make a large difference in injuries sustained and survivability (higher on the abdomen results in more internal organ damage - see the docs I linked earlier). What this thread is discussing is using a seat with a lap belt designed to be used with the pax in a seated position, but with the pax lying flat. That combination obviously puts the restraining belt in the wrong position for maximizing survival in a crash. The risk of injury or death from being improperly positioned relative to the lap belt in a seat likely far exceeds that from flying debris.
However, in my experience travelling in J, lap belts are not used at all! Instead a three point belt with some sort of padded airbag contraption are fitted to the belts. I suspect the purpose of these belts is to provide protection during all phases of the flight including whilst in the air where you may be expected to be in the lie flat position and where there is a non-trivial risk of severe turbulence. If you are travelling in Y or PY where a simple lap belt is used, you won't even have the opportunity to go lie flat. At most you'll have a slight recline. But the point this thread is making, I suspect is about J and F cabins whose safety systems are designed entirely differently from that in steerage.
Safe Travels,
James