Check
http://www.timair.net/service.htm I'm pretty sure they are the only ones that service Negril. Of course it's safe, those little planes have good glide ratios and if the engines fail they can just land softly in the ocean next to the hungry sharks.......kidding about the hungry sharks.
Be sure to post what you get for rates, I think the rate from Montego Bay to Negril is around $200