Factual error: The vents that Hunt and his sidekick crawl down at CIA Headquarters are standard galvanized steel box vents; they are very common in the building trade. Try walking or crawling down one - you'll make a noise like the sky is falling down. People will be able to hear you for miles. Every person in that building would know somebody was crawling about in the vent system. (This error applies to dozens of films, not only this one.)
Suggested correction: "People will be able to hear you for miles. Every person in that building would know somebody crawling about in the vent system." No, they won't. The sound from someone crawling through a vent would carry for metres but not miles. CIA Headquarters are quite large, so it's unlikely that the sound would carry to every part of it. And even if it did, there's no reason to believe that every person in the building would know that the sound was somebody crawling about in the vent system.
The galvanised steel the box vents are made out of makes a very distinctive booming sound when it distorts under pressure, and it is loud. Unless they are deaf, the people in the room through which the vent runs would know perfectly well that there was someone in there.
Factual error: Liverpool Street Station is shown as more or less deserted in the hours of daylight. The only way this could be achieved in real life is by phoning in a bomb threat.
Suggested correction: It's night. After Ethan sees that his parents have been arrested, he walks out in the streets, and it's dark outside. Several shots later the big clock in the station is shown, and you can see that it's about 11pm.
This validates the entry rather than correcting it. If it is 11.00 pm the pubs have just closed and Liverpool Street Station would be heaving. This is true of any mainline station in London - as well as the fast food restaurants associated with them. Any Londoner knows that.
Factual error: In the scene of the eurotunnel train the ticket collector is wearing a 70s British Rail uniform This was the national railway company for Great Britain but is now defunct due to privatisation in the 90s.
Suggested correction: At the time of filming, British Rail would still have existed as it was only being dismantled in the mid 90s. However, I think Eurostar would provide their staff with different uniforms.
Plot hole: In the famous raid on the computer room raid, where Hunt is lowered from the ceiling, we see a close up of the screws to the vent being undone and caught in a holder so they don't fall on the floor. But the screws cannot be put back in their holes and done up once the vent is closed, and there is not enough time for Hunt to be pulled back up and the vent closed and screws replaced when the operator returns to the room, as Hunt was pulled back up with seconds to spare.
Suggested correction: They would not have to use screws to reattach it. They could use tape, glue, or magnets.
That would be detected, but of course, the perpetrators would be long gone.
Plot hole: At the end of the tunnel, the helicopter has been attached to the train; Phelps knows it, the pilot knows it, and yet Phelps still climbs across to the helicopter like he's trying to escape, but there's nowhere to go. He's deliberately climbing into a potentially lethal situation he can't get out of for no reason except it makes it convenient to kill two bad guys with one explosion.
Suggested correction: Phelps detached the cable before he jumped to the helicopter. The problem was Krieger tried to kill Hunt first, before trying to escape.
