From Wiktionary:
Gangway: a passageway through which to enter or leave, such as one between seating areas in an auditorium, or between two buildings.
Aisle: a clear path through rows of seating.
Is the key difference here that a gangway leads to an exit door, while an aisle can just lead from one wall to the other in an auditorium or movie theater?
The question actually arose when I was proofreading a translation about a document storage area and noticed that the translator used gangway in the position where I expected to find aisle:
Control and measuring devices (thermometers, psychrometers, hygrometers) are placed in the main gangway on a rack away from heating and ventilation systems.