This question already has an answer here:
- Why are there two different brace positions (pictured below) ?
(If there is a difference between the official and true reason, please state both. In many planes the reduced seating spacing does not allow the pike position (on the right), but I doubt this is the official statement of airlines.)
- Are they equally protective ? If not, why are both recommended ?
- What arguments are there in favor or against each ?
- If available, statistical data and relevant links to studies and crash tests would be very welcome if they distinguish between the two positions.