Is it permissible for a pregnant wife to travel alone by plane, accompanied by a flight attendant, knowing that her family will receive her at the airport?

A woman is not permitted to travel without a mahram (definition), except for the obligatory Hajj and Umrah (definition), provided she is accompanied by trustworthy women. A mahram is her husband or a male whom she is permanently forbidden to marry, such as her father, son, brother, paternal uncle, or maternal uncle. The flight attendant is not suitable as a mahram for your wife. However, if your wife's travel is due to necessity or an urgent need, and she cannot find a mahram, then there is no objection to her traveling by plane.