Hi. First of all, thanks for such a great site. Very helpful and informative. I was wondering if you could tell me what the big white flashing-light X means at the beginning of a runway. recently i dropped someone off at LAS during a particularly bad thunderstorm. The winds were quite bad. Anyhow, planes were landing on the runway that comes in over Tropicana Avenue. I was watching one plane land over me as i was on tropicana and i noticed the big white X was flashing. At the last moment the pilot pulled up and did not land. did the flashing X tell him to do that, or is that X always flashing? What is it indicating? I just never noticed the X there before. Thanks for you help.