As Delta Tango 19 takes off from the airport, there is a shot where it is actually landing. This can be seen from the fact that there is no runway behind them, as it is in front of them.
When the Captain Scarlet series was sold to TV broadcasters, ITC (who had backed and then marketed the series) issued a "recommended broadcast order". This was not always the same order as the episodes had been made. Episodes 1 to 4 were made and broadcast "in sequence", but from episode 5 this no longer applied. Episode 11 ("Avalanche") was the 5th to be broadcast, swapping places with the episode "Point 783" which was the 5th to be made, but the 11th to be broadcast.