The kids can't afford plane tickets, so they morph flies with Tobias acquiring a fly morph. After Marco dabbles in a first-class passenger's Salisbury steak, the occupants on the plane are alerted.
Since the kids couldn't afford plane tickets, they transformed into flies using Tobias' fly transformation ability. Meanwhile, Marco tried some of a first-class passenger's Salisbury steak, which caught the attention of the other passengers on the plane.