It's almost worth the entire episode to watch the WWI biplane land at a 1959 SAC base in France. The hulking cargo planes make the 1917 relic look like a Tonka toy as it taxis under an immense wing. It's also a good graphic illustration of how the destructive power of air weaponry had grown over time-- and that was 50 years ago.
The drama itself is an engrossing exercise in time travel, as a WWI British pilot must travel forward in time and then back so that the future can remain the way it should be. If this sounds confusing, it is, because there's a paradox at it's heart and probably a logical contradiction. But then, that's why TZ remains a cultural landmark -- it was among the first, if not the very first, to use TV to challenge us about our most common-sense beliefs. And it did so in an engrossing way that keeps people as entertained now as it did then. This episode stands as a good example.