How airport security screening works

The global rulebook: ICAO Annex 17

Annex 17 to the Chicago Convention sets the international standards for aviation security. ICAO first adopted it in March 1974. An ICAO training module from September 2024 describes the Twelfth Edition, Amendment 18, which applies from 18 November 2022. It holds 95 standards, 21 recommended practices and 30 definitions in five chapters ¹.

Standard 3.1.1 requires each state to set up a written national civil aviation security programme. Standard 4.4 requires states to screen departing passengers and their cabin bags before they board an aircraft from a security restricted area. The screening methods must be able to detect explosives. Standard 4.5 requires hold bags to be screened before they are loaded, and leaves each state to define the detailed screening standards ¹.

Who runs the checkpoint

Annex 17 tells states what to achieve. It does not say who must employ the screeners ¹. Countries have chosen different models.

In the United States, the federal government took over screening after the attacks of 11 September 2001. The Aviation and Transportation Security Act of 19 November 2001 created the Transportation Security Administration (TSA) ^12,13. TSA employs screeners at most commercial airports. Under the Screening Partnership Program, set up in 2004, an airport can apply to use private screeners who work under TSA oversight ¹³. A TSA-funded study found that private screening airports performed at about the same level as federal ones, with cost differences that depended on airport size. In a 2015 review, GAO said the study's conclusions were not fully supported ¹³.

In the European Union, Regulation (EC) No 300/2008 sets common basic standards. Each member state must name a single authority for aviation security and run a national security programme and a quality control programme. Airport operators and airlines must each run their own security programme ². The detailed rules sit in Commission Implementing Regulation (EU) 2015/1998 ².

Screening people: metal detectors, scanners and hand searches

The European Commission tells travellers that they will be screened by walk-through metal detection equipment, by a hand search, or both ³. A walk-through metal detector finds metal objects. It does not find non-metallic items.

Security scanners, often called body scanners, fill that gap. The Commission says they can detect both metallic and non-metallic items carried on a person ⁴. EU rules make scanners optional for member states and airports. Where they are used, only scanners that do not use ionising radiation are allowed. The machines must not store, copy or print images. Any human reviewer must sit in a separate room and the image must not show the passenger's face. Passengers can ask for a reviewer of the gender of their choice. They can opt out and receive another method, including at least a hand search ⁴.

Screening cabin bags: X-ray and CT

Conventional X-ray machines produce a flat image of a bag. The Commission notes that traditional equipment of this kind cannot reliably detect liquid explosives, which is the reason for liquids limits ⁶.

Computed tomography (CT) scanners build a 3-D image. TSA says its CT units apply an algorithm as they generate a 3-D image of the bag, and officers can rotate the image on screen. At airports with CT, TSA lets travellers leave electronics larger than a mobile phone and their 3-1-1 liquids in the bag ¹¹.

Before equipment reaches European airports, it is tested. The European Civil Aviation Conference (ECAC) runs a Common Evaluation Process (CEP) that tests equipment in laboratories against ECAC/EU performance standards. In January 2020 the European Commission accepted the CEP as a precondition for EU approval of security equipment. The US TSA joined the CEP as an Associated Authority on 9 June 2025 ¹⁴.

Liquids rules in the UK and EU, 2024 to 2026

The 100ml liquids rule dates from 2006, after a plot to blow up aircraft departing London Heathrow with homemade liquid explosives. EU rules limit liquids to containers of 100ml or less, packed in one transparent resealable bag of up to one litre, with exemptions for medicines, baby food and special diets ⁵.

New cabin bag scanners led some airports to relax the limit, then reverse course. On 7 June 2024, the UK Department for Transport said the 100ml limit would return temporarily from 9 June 2024 at six regional airports running next generation checkpoints ⁹. On 31 July 2024, the European Commission said the 100ml limit would return from 1 September 2024 at EU airports using Explosive Detection Systems for Cabin Baggage. The Commission called it a precaution over a temporary technical issue, not a response to a new threat ⁶.

In 2025 the EU moved to lift the limit again for approved equipment. Euronews reported on 25 July 2025 that ECAC had approved a tested solution in June 2025, and that each manufacturer still had to submit its own equipment ⁷. On 5 August 2025, Italy's civil aviation authority ENAC said several Italian airports, including Milan Linate, Bologna and parts of Milan Malpensa, would accept containers of up to two litres. CAPA reported that the change applied to airports using approved Smiths Detection equipment and that airports with other equipment kept the 100ml limit ⁸.

As of 19 October 2026, rules still vary by airport. GOV.UK says most UK airports keep the 100ml limit, some allow containers of up to 2 litres, and travellers should check each airport on their route, including the return ¹⁰. The European Commission's traveller guidance still lists 100ml as the standard EU rule ³.

Hold baggage screening

Annex 17 requires every originating hold bag to be screened before it is loaded on a commercial aircraft, with methods able to detect explosives ¹. EU common basic standards cover screening of hold baggage, cargo, mail and airport supplies ².

Annex 17 leaves each state to define the detailed standards for hold baggage screening ¹. In Europe, screening equipment goes through the ECAC laboratory tests described above before it gains EU approval ¹⁴.

Who pays: security fees

Passengers often pay for screening through a fee on their ticket. In the United States, the September 11 Security Fee is $5.60 per one-way trip that starts at a US airport, capped at $11.20 per round trip. Airlines collect the fee when they sell the ticket and pass it to TSA. TSA lists Public Law 113-294 of 19 December 2014 as the most recent legal change ¹².