Interesting answers
I presume you are flying in a pressurised aircraft and so you are depressurising to about 8000 ft. As a result the gas in your guts will expand. Most people notice some abdominal distension but you are to put it mildly more aware
The two reasons that spring to mind are
1 you are air swallowing so there is more gas in your stomach. This can be due to eustatian tube issues or anxiety or boredom!!!!! Might be worth excluding the former
2. You have more gas in your guts already. This may be diet dependant such as a high roughage diet. Equally chronic constipation may be a exacerbating factor.
I would suggest you see your family doctor to explore these issues in the first instance