[QUOTE=skywardhunter;25736152]well... this is a weird thread to stumble upon. I think the obvious reason must be pressure differentials, my concern would be if you've got a vein/artery popping in down there what if it happens somewhere more dangerous like your brain... not to be alarmist[/QUOTE
The type of answer above is what makes internet discussion groups so unreliable. The person voicing an opinion (skywardhunter) clearly has no medical background whatsoever and is "shooting from the hip". He has no idea how ridiculous his answer is, and may, unfortunately, lead other people astray.
Blood in the ejaculate is a relatively rare finding, especially in older men. Its occurrence has nothing to do with altitude, pressure, or length of a flight. While a doctor exam is suggested for an initial episode, most cases will resolve spontaneously. See
http://www.harvardprostateknowledge....ia-demystified
Shame on skywardhunter for nonsensically speculating about "obvious reasons" and other unlikely consequences of air travel.