I just happened to see 2 747's (-400) yesterday. They were operated by Delta Airlines, the only 747 operator at my hometown airport. (sad, I know). So, the first one was fairly low (but fairly high at the same time) and I could see the individual engines. It was a cold day, so the contrails were long and defined. There were only three contrails; the number 1 (?) engine or the one on the far left by the aircraft's perspective was not there. I thought that was odd, but later, I saw yet ANOTHER 747 (woo-hoo! It must have been my lucky day!) flying really high but you could still definitely see the contrails. Again, there were only three with the number 1 engine off, the same one as the earlier 747. Both had started their descent, but both were still >5,000 ft by my estimate. Is this normal, or is Delta so cheap that it shuts one of its 747 engines off? I wouldn't be surprised, because it crammed seats into its 747's that are 0.2 inches SMALLER than its A319 seats, which, believe me, are small and uncomfortable. Thanks for any info or opinions on this!