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On a recent trip from San Diego, California, to West Lafayette, Indiana, Candis Dorsch's husband developed a profuse nosebleed. "It wouldn't stop," she recalls. "It was obvious to us he could not fly without endangering himself, other passengers or the crew. It was obvious he needed medical attention."

http://edition.cnn.com/2008/TRAVEL/traveltips/05/29/flying.sick/index.html

Does "On a trip" imply the person is already on the way in general? In this context, is he already on the plane flying to his destination? If not, how should I interpret it?

Thanks in advance!
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New2grammarIn this context, is he already on the plane flying to his destination?
Yes, I would say so. All the other facts in the passage indicate this.
In general "on a trip" includes all the events from the time of leaving to the time of returning, not necessarily only travel time.
If I say that I lost my wallet on a trip to Paris, I may certainly have lost it in the city of Paris, not on the plane to or from Paris.
(But as I said above, in this example it's clear that the incident occurred on the plane.)
CJ
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Rare is the day that I disagree with Jim, but I don't think "It was obvious to us he could not fly without endangering himself, other passengers or the crew " implies that he was already on the plane at all. On the contrary -- I think it implies that his family didn't think he should get on the plane. (Probably for the return flight, since he was already "on the trip.") And, if you click on the link and read the whole article, that's in fact what was going on -- the family was trying to convince the airline to allow them to change their reservation without losing all the money they paid for the tickets.

And, if you read the whole article, you will be even more disgusted with the current state of air travel. Does anyone remember when flying was sort of fun, and even sort of luxurious? And you could change your plans, without having to actually be dead, and not have to pay for a new ticket? And you didn't have to sit next to someone who was bleeding uncontrollably? Ah, those were the good old days.
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Comments  
In general "on a trip" includes all the events from the time of leaving to the time of returning, not necessarily only travel time.

Thanks, CJ. That's a very good point!
 khoff's reply was promoted to an answer.
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