I am booking a holiday to Los Angeles from Dublin. The flights I am looking at will not be direct and have a 1 1/2 hour layover in Heathrow. I am aware that in Dublin if you are flying to America directly you fill out preclearance forms so that you do not have to do this when you arrive. As I would be flying then from heathrow I would probably have to fill out the forms there. Would I have time in 1 1/2 hours? I can't find information on this anywhere?

  • 3
    LHR doesn't have US pre-clearance, so on your return flight you'd go through immigration and customs in the USA not Heathrow
    – Gagravarr
    Sep 3, 2016 at 12:42
  • 1
    @Gagravarr: That's an answer! Sep 3, 2016 at 12:45
  • the form takes about 5 minutes to complete. Ensure you have a pen, your passport, and the US address where you will be staying. Sep 3, 2016 at 13:28

2 Answers 2


If your itinerary is DUB-LHR-LAX, then that Dublin and Shannon have US Pre-Clearance facilities is pretty much irrelevant. Your DUB-LHR flight, while not technically domestic, is essentially similar since you shouldn't have to enter the UK during transit.

You will clear US Immigration and Customs at LAX. You should expect to get any required forms* from the cabin crew sometime during the LHR-LAX flight.

*CBP has notably automated their processes now. BA, presumably, will play a video before arrival that describes the process and what travelers are exempt from what procedures.

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    Minor correction: the card you fill out in flight is a Customs Declaration, CBP Form 6059B. Paper I-94 forms are not used anymore for arrivals by air. Sep 3, 2016 at 13:15
  • Yeah, updated. I've been saying/thinking I-94 for so long.
    – DTRT
    Sep 3, 2016 at 13:30
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    It might be worth emphasizing that LHR does not have preclearance, since it seems like OP is under the misconception that it does. Here is the list of preclearance airports: cbp.gov/border-security/ports-entry/operations/preclearance Sep 3, 2016 at 13:33
  • okay, I understand this better now and thanks for the helpful answers! Just to check up, you think that this layover time is long enough to make the second flight considering they are booked within separate airline and I will have baggage in the hold to collect?
    – adam
    Sep 3, 2016 at 13:47
  • That's a totally separate question and there are many factors involved. You should open a new thread, but it will likely get redirected to many similar questions and answers.
    – DTRT
    Sep 3, 2016 at 13:49

The question is base on a misconception of US preclearance. For practically every country, once you arrive on their soil from outside[1] you are subject to passport controls and customs inspection. This means that:

  • you can only arrive at ‘international airports’, i.e. those that have these facilities
  • if there are a number of flights arriving at the same time, customs and immigration may be very congested.

Preclearance was introduced to combat these points, originally by a request of American Airlines who presumably wanted to operate flights from Toronto to ‘non-international’ US airports (where immigration and customs cannot be performed on arrival due to lacking facilities). Its concept is to ‘outsource’ all immigration and customs checks to foreign soil, before a plane’s departure. This renders an international arrival something that seems like a domestic arrival from the arrival airport’s point of view. And it makes sense from a time-economic point of view: passengers typically arrive at the departure airport many hours before their plane leaves, so why not use that spare time so that they can make quicker connections on arrival?

The big downside to preclearance is that it requires those facilities at the departure airport and it also requires a bilateral agreement between the US and whichever country the airport is in to allow for US CBP to perform their duties in foreign countries.[2]

Your suggested itinerary, however, completely defeats the idea of preclearance. Say you are in a plane with 200 other passengers on your way to Heathrow from Dublin. You might be travelling on to the US and maybe ten others, too. That leaves 190 passengers in that plane not going to the states that don’t need to (and don’t want to, and must not) go through preclearance — they will not enter the US.

You could make arrangements to have somebody else smuggle some customs-relevant item onto your Dublin–Heathrow plane that you then intend to get past the US customs as you already went through preclearance. That would create a massive loophole. Therefore, preclearance is only possible for those flights that depart for the US without further ado.

And what about your Heathrow–US flight? Well, Heathrow airport does not have preclearance facilities.[3] So you cannot go through preclearance there.

[1]: Sometimes, outside does not only mean outside the country but outside of a greater set of countries. E.g. Arriving in Germany from the Schengen area or in the UK from the Repulic of Ireland (as part of the Common Travel Area) is basically treated as domestic travel.

[2]: Typically, the US CBP has less possibilities when operating on foreign soil. For example, they do not have the power to arrest travellers outside of the US, and they cannot force people to allow searches. They can, however, prevent boarding.

[3]: Plans exist to extend preclearance to a number of additional airports; Heathrow is amoung them. (Homeland Security press release)

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