The span-wise flow is caused by the difference between the air pressure on top and beneath the wing and its direction of movement goes from:
Domanda 239, Principles of Flight - ATPL - Airline Transport Pilot license
| Beneath to the top of the wing via the wing tip |
| The top to beneath the wing via the leading edge |
| Beneath to the top of the wing via the trailing edge |
| The top to beneath the wing via the wing's trailing edge |
