This looks interesting (although much of it is too technical for me), and also seems to indicate that 38,000' is not the highest allowable flight level (were you just arbitrarily throwing out that figure?). It looks like it was 40,000' (at the time of the writing of this piece), with even higher levels envisioned with increasing technological advancement. If memory serves, I think I also recall being in a commercial airliner at either 39,000' and/or 41,000' in the past 5-10 years.
CaT
