Thank you for your query.
Normally, airlines allow travel in case of uncomplicated pregnancies ( no history of finding of preterm labour, no medical complications, singleton pregnancy
etc ) upto 30 - 32 weeks, beyond which you require a certificate allowing travel by your obstetrician.
However, each airline has its own individual policy variation and you need to check with the airline you are planning to fly with.
Also, the 5th and 6th months are relatively safe for short air travels.
Only your treating obstetrician would be able to evaluate you and advise you if there are any risks or contra indications for travelling.
Please take care and do the needful