Plot hole: In order to build up suspense, Virgil and Brains stand on the Crab Logger as its dangerous fuel is pumped out, despite the fact that it is hanging on the edge of a precipice. In fact they could have left as soon as they had plumbed in the pipes to empty the fuel tanks - the whole procedure is controlled by Scott in Thunderbird 1 and they make absolutely no contribution to the operation at all. They do not need to disconnect the pipes; they are left behind and dropped from Thunderbird 1 as planned. They just stand there chatting about how much danger they are in until jumping clear at the very last second. Silly buggers.
Revealing mistake: Near the end of the episode, Thunderbird 2 lands and reverses into its hangar. During this bit, if you look carefully you can see white smoke near the boiler on the far side of the hangar, only this smoke is apparently being sucked into it. This is the usual footage of Thunderbird 2 exiting the hangar played in reverse. (00:42:05)
Continuity mistake: At the beginning of the episode, we see the models of Thunderbirds 1, 3 and 4 on the table next to Nicky and you can see that Thunderbird 1's nosecone near the edge of the table. But when Nicky asks for Thunderbird 3 to be launched, we see a close up of the model, and Thunderbird 1 is now situated next to Thunderbird 4.