I am a flight attendant for United so I'll give ya the lowdown. Ch 9 is available on all UA aircraft with the exception of the 737-200...they are the only eqipment in our fleet that are not equipped with an inflight entertainment system. Every other aircraft in our fleet (all 747-400s, 737-300/500, 727, 777, 757, 767-200/300/ A319, and A320) have headsets in each seat pocket. This is because we don't charge for movies anymore so every flight is an entertainment flight. CH 9 is at Captain's discretion though, so it may not be available on every flight. When you get on one of our planes, plug into the armrest with our headsets or your own (with the exception of coach class on the 727...they don't have electronic jacks...just the old pneumatic ones) and dial up CH 9. If you hear Rock music, the cockpit has it shut off. Just ask one of us if the Captain would turn it on. Sometimes they forget or leave it off until a passenger has requested it. Sometimes they tell us in our preflight briefing that it will not be available at all...some cockpit crews don't like their passengers to listen in. As far as emergencies go, a pilot told me that in the case of an inflight situation, turning off CH 9 is one of their items on the checklist...this was the case in 1989 with flight 232...the DC-10 that crashed in SUX. I hope this info has been helpful.