What are my chances of contracting tb after being exposed to someone with active tb on a plane to japan?

PTB: Infection occurs by inhalation of droplet containing the mycobacterium through coughing. So if you are seated next to someone with active ptb, try to cover your mouth or change your seat.

Very low: TB is a very slow growing germ that is relatively hard to transfer. Simply sharing the air in a long plane ride is unlikely to do it. Sit next to someone who is coughing repeatedly would be a higher risk. The usual risk group includes those who live with someone with active TB and are exposed on a daily basis for weeks/months.