This is one of two episodes (the other is Confetti Check A-O.K. (1970)) that does not begin with the standard opening sequence.
The cast includes a number of prominent and soon-to-be-famous actors, notably guest star Mike Pratt (Clem Mason), who was concurrently co-starring in the popular comedy-drama 'My Partner the Ghost (1969)', and Christopher Timothy (the SkyDiver 3 navigator) who gained international fame a few years later with his starring role as 'James Herriott' in the hugely popular rural drama 'All Creatures Great and Small (1978)'.
This episode introduces Skydiver's cave dockyard.
The red mini dress worn by Deborah Grant (Linda Simmonds) in this episode was previously worn by Susan Jameson (as Anne Stone) in The Sound of Silence (1971) and would later appear worn by Kirsten Lindholm in Timelash (1971).
At 45:21 the actress' teardrops are obviously glycerin as they are in the same position each time the camera returns to her face.