Pit of Peril - S1-E2
Other mistake: When the atomic reactor goes down 20 points in the Sidewinder, look at Frank and you can see his left eyebrow is missing.
Thunderbirds (1964)
1 other mistake in Pit of Peril - chronological order
Starring: David Graham, Ray Barrett, Peter Dyneley, Shane Rimmer
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.
Trivia: Jeff Tracy's five sons were named after Mercury astronauts - Scott Carpenter, Virgil Grissom, Alan Shephard, Gordon Cooper and John Glenn.