barometric switches is old technology back to the '70s, how to blow up an airplane with these. very hard to detect. the security in sharm el-sheikh, getting a bomb through there, yes, it's possible. >> david, if it's possible it was a bomb, how big of a bomb would it have had to be? we're talking about 224 people on board. this was a big jet. >> well, the pressure differential in an aircraft is maintained at about 9 psi-d, differential. if the pressure exceeds that, up to 15, 16, it can fracture the hull or the structure of the aircraft. so to get it from 9 psi-d to a 15 or 16 psi-d is not that hard to do. it takes just a quickly accelerated mass of air so the bomb would not have to be very