Falling action is the last thing that happens before the resolution. It follows the climax, or the turning point of the story. The falling action here occurs when David and Rosalind are hiding and the Sealand arrive to rescue them.
Falling action is all that occurs after the climactic point at which the ultimate course of the resolution is set. In this case, the falling action is all that happens after Joseph Strorm sets out in pursuit of David, Petra, and Rosalind. At the point of pursuit, the course to the resolution is set--there is no going back, there are no further options for David or Petra or Rosalind--and all that follows is falling action leading down the disaster strewn path to the resolution.
The falling action is the section of the plot that comes between the climax and the resolution. In this case, it is the face-to-face meeting of the Sealand woman and the telepaths that occurs after the Sealanders have arried on their helicopted and indiscriminately killed Waknukians and mutants alike, and Michael's decision to not leave with the others but to go back for Rachel.