I mostly fly AS and AA - but when I do fly BA and CX, I notice the safety video talks about the brace position. (The CX video seems a little more dramatic on this.)
Now, it makes sense that on AS/AA flights we don't need to know about the brace position, because of __<insert your own humorous reason here>___... but it gets me thinking... what's the correct/proper brace position.
Using Google Image Search, I see a lot of different brace positions. Arms under your legs. Arms crossed resting on the seatback. Hands over your head and against the seatback. (But I know not to interlace - or you end up with broken fingers. Oh, and take off the ol' glasses.)
Which one is the best/most proper?
I think that the important thing about the brace position in a survivable crash landing is two-fold: to get your body down below the seat backs to protect your head and body from debris flying through the cabin during the deceleration and break-up following ground or water impact; and, to the maximum extent possible, keep the arms and legs from whiplashing around.
I would think that you are physically closer to the floor and could follow the emergency lighting easier if there was fire and smoke.
I remember an accident investigator telling me that the most frequent cause of death in most
survivable crashes is internal bleeding caused by the aorta ripping from the heart as a result of large G-forces resulting from the rapid deceleration. My hunch is that the aorta can withstand higher G's in the axial direction than in the radial direction. You would place those organs in the axial direction in the brace position.