Ah yes... Reminds me of the time I was a lowly DC-9 FO working a flight from MSP to MOT (that's Minot, ND, for all you civilized folks..) Anyway, we get handed a -9 with an MCO'ed AUX HYD pump, which carries a HUGE HUGE takeoff weight penalty. (Interjection for anyone who hasn't had the pleasure of flying a Douglas product... The AUX pump basically exists to retract the landing gear in the event of a right engine failure on takeoff. It does other stuff, but that's the big ticket item.) Anyhow, being a good (well, not good necessarily, but marginally competent) FO, I looked up the MCO, noted the HUGE HUGE takeoff weight penalty, and suggested we talk to dispatch about getting another plane.After all, given the HUGE HUGE weight penalty, we'd be able to take about 30 people (which equals 10 North Dakotans) out of Minot once we got there. The good Captain agreed, and promptly called the dispatcher. The good dispatcher agreed, and promptly got us a new airplane. Easy as pie, until it came time to deplane....

At which point, the good Captain got on the PA, told the passengers we had a mechanical situation that required us to change airplanes, and then proceeded to tell them everything they did not EVER need to know about back up hydraulics, engine failures, gear retraction, and second segment climb requirements. I wish I could say I was making this up, but the words "flaming ball of wreckage" were actually spoken....

The original plane was full. The replacement plane was not. Good times.