Complex sentence: The plane takes off and starts with a relaxing journey, Alex spots Mort clinging to the wing of the plane and waves to him (causing Mort to wave back and fall off the wing into the sea).
Split into simpler sentences: The plane takes off and starts with a relaxing journey. Alex later spots Mort clinging to the wing of the plane and waves to him (causing Mort to wave back and fall off the wing into the sea).