As Fireflash makes its first landing attempt onto the elevator cars, the radio control elevator car on the left can be seen to bear the number 4, even before car 3 had crashed and car 4 had left the pod.
At the end of "Trapped In The Sky", a doctor visits Tracy Island to examine Kyrano, and "Operation Cover-up" disguises all evidence of the International Rescue organization in the lounge, with the portraits of the brothers in uniform replaced by pictures of them in civilian clothing. But when the doctor enters the room, the in-uniform portraits are still visible in shots of Scott, Gordon and Jeff.
In several shots from beneath Thunderbird 1, seen while the Hood takes photographs of the aircraft, the vehicle's markings show the "T" of Thunderbird painted on the red nose cone. All other shots of the craft show the nose cone free of markings.
Footage showing Thunderbird 2 leaving with Pod 3 (pods 2 and 4 seen either side) is often reused, even when you see the craft select another pod.
As the pods move under Thunderbird 2 it is obvious there is not enough space between the pods for the rafts wings, but when it starts to move out of the hanger there is space between the pods for the aircrafts wings.
Thunderbird 5 has "International Rescue" written over the windows but it is written so it is readable only from the inside (i.e. backwards from the outside) so the only ones who could ever read it would be John and Alan.
Not long after takeoff, the Fireflash is ordered to level off at 200,000 feet. Billowy cumulus clouds are visible at that same level outside the cockpit windows, but even the highest basic clouds rarely exceed a height of 50,000 feet.
In many of the interior shots of the Fire Flash aircraft, the view through the outside window is still, meaning the craft is apparently not moving at all (and it is supposed to be approaching mach six!)
The "Fireflash" model was flawed. It's port wing was quite noticeably warped downward. This was very uncharacteristic of Gerry Anderson's productions.
The crew of the Fireflash apparently only tell the passengers of the bomb threat when the mid-air boarding attempt is made. However, since the plane had already made violent aerial maneuvers to attempt to dislodge the bomb, wouldn't the passengers have already noticed the plane moving around like that and have wondered why?
At around the 34:30 minute mark, Virgil mistakenly says "Thunderbird 1" over the radio rather than "Thunderbird 2" which is the craft he pilots.