This appears to be a duplicate of Why does connecting flight need a security check at connection airport? but the accepted answer IMO simply doesn't apply to my specific example.

In many "good" airports arriving passenger simply exit the gate into the departure area and they can either walk to their connecting gate or through the baggage claim and out the door. For example in FRA if you arrive from the US in concourse Z and you transfer to a Schengen flight in A you just go through passport control between Z and A but not through security again. European airports like this are BRU, FRA, MUC, VIE, ZRH, etc.

Examples of the "bad" layouts in Europe are LHR or CDG. All connecting passengers get funneled through long corridors to a single collecting point where they have to go through security again before they can enter the departure area.

  1. It's bad for the passenger in terms of inconvenience and time. LHR seems to be particularly annoying: long lines that are poorly staffed, no priority lanes, etc.
  2. It's bad from a Covid mitigation perspective: being jammed in a line for a long time is probably the single riskiest activity of travelling. Social distancing in security lines is NOT practical.
  3. It's bad for the airlines, since they have to increase their minimum connection times and have to deal with way more variable transfer times and missed connections.
  4. It's bad for the airport since it takes up a lot of space, people and money.

So this begs the question why? The accepted answer states

There are locations that fly to LHR that do not conform to international norms regarding international safety.

This may be true, but it would apply to other airports the same way. They aren't a lot of location that fly to LHR but not to FRA. There ARE flights from Lagos to FRA as well.

To clarify the question: what is different between, say, LHR and FRA that would cause LHR to add significant cost, stress, time, insecurity and inconvenience to a connection? Why does LHR think this is necessary and FRA thinks it isn't?


I focused this questions specifically on European airports to make the comparison as "apples to apples" as possible. I've seen discrepancies in other airports as well. In DOH and IST I had to go though security recently but I don't think we had to in DXB. KEF is also a no. US & Canadian airports are different since they have no international transit. Domestic transfers do not require security.

Overall this seems mostly random with no obvious reason to do it one way or the other. Hence the question: is there a rhyme or reason ?

  • Comments are not for extended discussion; this conversation has been moved to chat.
    – Willeke
    Dec 12, 2022 at 11:32

2 Answers 2


Your description of when additional security is performed is missing one important fact. To use your example airport of FRA, you've stated that there is no need to re-clear security when connecting from another flight. This is NOT always correct.

Many airports, including Frankfurt (FRA), will determine whether a passenger needs to re-clear security based on the origin of the flight they are arriving on. As you've stated in your question, when arriving from the US into Frankfurt there is generally no need to re-clear security. The same is also generally true for flights from other EU countries. (I say 'generally' because airport officials always have the ability to force an extra security check for passengers from these flights if they feel there is a need).

However many flights from other countries DO require clearing security on arrival in Frankfurt - in fact it's a legal requirement that they do so under EU legislation. Any passenger arriving from an airport/country that hasn't agreed to enforce the EU's security standards is required to pass through security before being allowed into the departures area of the airport.

Rather than having to maintain separate arrival areas/gates/corridors for flights based on the origin of the flight, some other countries/airports take the more simple approach of forcing all connecting passengers through security before they are able to enter the departures area. London Heathrow as you've mentioned takes this approach.

There is an additional model which is worth mentioning, which is what used in the US. All passengers arriving into the US on international flights (with the exception of flights from a small number of "pre-clearance" airports where immigration/customs formalities are carried out at the point of departure) are required to pass through immigration and customs on arrival in the US. Passing through customs means that passengers have had access to their checked luggage, which in itself necessitates them re-clearing security as otherwise they could have removed items from their check luggage and carry them onto the plane.

You mentioned having to pass through security in IST (Istanbul, Turkey). Istanbul actually uses the same model as Frankfurt, in that it depends on the airport your flight is arriving from. For some flights, presuming you already have a boarding pass for your connecting flight, you will be allowed directly enter the departure airport without re-clearing security. For other flights, all connecting passengers will need to re-clear security.

Domestic transfers (in any country) would generally not require passing through security as the security rules at the origin airport would be the same as at the destination airport, given that they are both in the same country. However even then there are exceptions. For example, Australian security rules are different for flights on very small planes (eg, sub-30 seaters) that generally only fly from remote airports that do not have the resources to enforce security as would otherwise be required. When one of these flights arrives into a major airport (eg, Sydney) the passengers are forced to re-clear security due to them not having passed through proper security at their origin airport.

  • 1
    This explains that both at FRA and at LHR some passengers need to go through security again and some do not. FRA arranges things in a way such that only those that need to go through security do so, LHR does not. OPs question asks why, which I feel is not really addressed in this answer.
    – quarague
    Dec 12, 2022 at 6:38
  • India requires passengers to re-clear security for domestic connecting passengers.
    – gparyani
    Dec 12, 2022 at 7:21
  • 3
    One complication is that some airports have (often due to how they expanded over the years) complicated paths between terminals that not always can separate passengers from "secure" and "non secure" origins. An example is ZRH where from concourse D to E you always have to clear security again, because there is only one path between the two, and they are used by passengers from all origins. Dec 12, 2022 at 7:42
  • 1
    @MichaelHarvey Everyone is welcome here but IATA codes seems to be the culture here. Some airports doesn't even have the name of the city in their name and many are named after small villages. If you don't know them you will have to look them up anyway, so the three letter codes are convenient and you can often guess them. City name + airport name would be an option but it is much longer. There is no requirement to use the codes though, I believe you just have to look them up and learn when you see them.
    – Anders
    Dec 12, 2022 at 23:29
  • 1
    @MichaelHarvey Many large cities have multiple airports, so people say FRA instead of writing out "Frankfurt am Main Airport." Saying Frankfurt Airport is ambiguous between Frankfurt am Main, Frankfurt Egelsbach, and Frankfurt–Hahn. On top, a typo at the travel agent might get somebody sent to Frankfort, Kentucky in the US.
    – user71659
    Dec 12, 2022 at 23:32

Everyone else addressed the security concerns, so I'll address another part of your post.

It's bad from a Covid mitigation perspective: being jammed in a line for a long time is probably the single riskiest activity of travelling. Social distancing in security lines is NOT practical.

The exact same question was often asked in the context of terrorism: isn't it bad for thousands of people to be jammed in security lines, creating a perfect opportunity for an evil person? The answer is... sure, it's a risk, but no one believes in that risk seriously enough to do something about it. So with the exception of Israel, every other country lets giant dense lines form in unsecured areas of their airports.

The same applies to COVID as of December 2022: with the sole exception of China pretty much every other country has decided that the risk of the virus spreading is too insignificant to actually do something about it, so no one cares if a few thousand extra cases show up every year because these security checks. This might the right or the wrong decision but at the end of the day that's the equilibrium and there's not much anyone can do about it.

  • 1
    China (at least pre-Covid, I haven't been back since) addressed it somewhat--there's often a metal detector/bag x-ray as you enter the terminal itself. It's not nearly as strict as the airside security but it's enough it would be hard to get a large bomb through it. Dec 12, 2022 at 3:12
  • 2
    @LorenPechtel Are there no lines to said metal detector during rush hours?
    – JonathanReez
    Dec 12, 2022 at 4:06
  • I don't know what the busiest times are. I've never seen more than a very short line. It's drop your stuff on the belt, walk through the hoop, pick it up on the far side. China uses such security points in many situations, not just the airport. They're not going to catch artfully-concealed non-metallic things but if they're paying attention it's not going to be easy to get a big boom past them. Dec 12, 2022 at 4:13
  • The fact that many countries have decided not to mitigate COVID doesn't mean this practice isn't bad for COVID mitigation. Dec 12, 2022 at 11:31
  • @user253751 sure it might be bad but… no one cares at this point.
    – JonathanReez
    Dec 12, 2022 at 14:03

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