THE growing certainty that the mid-air destruction of a Metrojet airliner flying from Sharm el-Sheikh to St Petersburg was caused by a bomb placed in the baggage hold has led to predictable calls from politicians for tighter airport security across much of the world. “What we have got to do is ensure that airport security everywhere is at the level of the best,” said Philip Hammond, Britain’s foreign secretary. “That may mean additional costs; it may mean additional delays at airports as people check in.” The deaths of 224 people aboard the Airbus A321 is a tragedy. But if passengers groan at ever more intrusive security screening, they are right.

Airliners are exceedingly tempting targets for jihadist terrorists, particularly those wanting to attack the “far enemy” in the West. Inspired by its success on September 11th 2001, al-Qaeda and its offshoots have sought several times since to strike at aircraft. In 2006 an ambitious plot to bring down several planes crossing the Atlantic simultaneously was foiled by good intelligence work. In 2010 a tip-off from a Saudi agent working for the British helped uncover an attempt by al-Qaeda’s Yemeni branch to send bombs disguised as printer toner cartridges to Chicago. Richard Reid, the “shoe bomber”, and Umar Farouk Abdulmutallab, the “underpants bomber”, tried to set off explosives on board airliners before being subdued by their fellow passengers.

Two things are striking about these events. The first is that, despite the terrorists’ fascination with blowing up airliners, attempts to do so are actually rather rare. Unless the Malaysia Airlines Boeing 777 that disappeared last year was brought down by terrorists (the most probable theory remains pilot suicide) the explosion of the Metrojet A321 over Sinai is the first major success they have had against an airline since 2004, when two Russian planes were blown up. The second striking thing is that the enhanced airport security introduced after the terrorist attacks of 2001 played no role in thwarting any of these attacks.

Hamming it up

Officials responsible for airport security argue that the system of checks and screening that take place at every airport, albeit with varying degrees of rigour, are the main reason for the absence of successful attacks. Perhaps they have served as a modest deterrent. But there are legitimate doubts about how much the kind of security currently inflicted on passengers really contributes to their safety.

The prohibition on carrying liquids on board, introduced in response to the method of mixing chemicals to explosive effect revealed by the 2006 plot, is a case in point. If security staff find illicit liquids that a passenger has not presented, they deliver a ticking off and confiscate the containers, but still allow the passenger to fly. Discovery of a gun or bomb, by contrast, would result in immediate arrest and almost certain punishment. Despite the mild consequences, it appears that nobody has been apprehended trying to get liquids on board to combine into a bomb in almost a decade. Nor have there been any reports of a would-be shoe bomber being intercepted despite the requirement for passengers to remove their shoes, brought in after Mr Reid’s cack-handed effort.

It could be that both security measures are so effective that they have completely deterred would-be terrorists from trying these methods again. Or it could be that they are essentially a performance to reassure passengers. Most experts incline towards the latter view. Philip Baum, a security consultant and editor of Aviation Security International, calls it “security theatre as opposed to security reality”.

America’s Transportation Security Administration (TSA), an agency of the Department of Homeland Security (DHS), has a budget of more than $7 billion a year; it also has access to the most advanced scanning technologies money can buy. Critics say it has not foiled a single terrorist plot or caught a single terrorist in the past decade.

Bruce Schneier, the chief technology officer of Resilient Systems, a security firm, points out that whereas the TSA catches plenty of guns and knives inadvertently packed by passengers, it is less good at spotting more determined attempts to get bad stuff onto aircraft. In June its acting head was “reassigned” after a so-called “red team” appointed by the inspector-general of DHS succeeded in getting fake bombs and weapons through the screening process in 67 out of 70 tests carried out in airports across America.

Why such a dismal record? “My guess is that it’s a combination of things,” reckons Mr Schneier. “Security screening is an incredibly boring job, and almost all alerts are false alarms. It’s very hard for people to remain vigilant in this sort of situation, and sloppiness is inevitable.” Mr Schneier also points to technology failures. Screening technologies are poor at detecting PETN, an ingredient of the explosive Semtex, carried by the underpants bomber. A disassembled weapon has an excellent chance of getting through airport security. Mr Schneier reckons that the only worthwhile security changes that happened after the 2001 terrorist attacks were the introduction of locked, blast-proof cockpit doors (the al-Qaeda terrorists used knives to take over the planes) and the willingness of passengers to intervene if they see somebody behaving oddly.

Some security experts argue that one of the greatest vulnerabilities at airports comes from what Mr Baum calls “the insider threat”. The working assumption is that the Metrojet bomb was placed in the hold by a baggage handler or by someone who had airside access (another possibility is that the bomb was placed in a passenger’s luggage by a hotel worker and was not picked up by airport scanners). It was probably detonated by a barometric trigger device when the plane gained altitude.

Mr Baum reckons that the airport at Sharm el-Sheikh is no worse than many others at vetting staff. He says that at British airports there are many people working airside who follow jihadist social media and that at some big American airports employees are not screened on their way into work if they have an ID card. Nobody is more dangerous than a psychologically disturbed pilot, as Andreas Lubitz demonstrated when he killed 150 people by flying his Germanwings Airbus A320 into a mountain earlier this year.

Some clue as to how easy it would be to put a bomb into somebody else’s bag comes from the number of valuables stolen from checked-in luggage. In the four years to 2014 passengers filed over 30,000 reports of missing property with the TSA. This year police at Miami International Airport used a hidden camera to film baggage handlers rifling through bags in a plane’s hold and stealing whatever took their fancy. Security experts reckon such practices are widespread.

The main reason why airport security is so bad, says Mr Baum, is that it tries to find things instead of focusing on the people who might carry them. Issy Boim, a former Shin Bet officer who worked closely with Israel’s airline, El Al, argues that whereas the Americans are looking for weapons, the Israelis “are looking primarily for the terror suspect”. Mr Baum is a strong advocate of what is known as “profiling”— building a picture of both passengers and airline staff. He rejects the idea that this has to be based on crude stereotyping (being suspicious of all young Muslim men, for example). It should be based on behaviour both prior to flying—for example, when, how and where a ticket was purchased—and at the airport itself.

El Al employs people who have been trained in psychological observation techniques to interview every passenger before he or she is cleared to go through physical screening. Anyone who arouses their suspicion is subjected to a further grilling and may well not fly. El Al is thought to use some profiling techniques that would be politically unacceptable in Europe or America. Hebrew-speaking Israelis can expect to get off more lightly than Arabs and single white women, for example. But as Mr Baum points out, customs and immigration officers at airports in the West commonly use profiling, “and it works”.

El Al also spends more than other airlines on other types of security. Hold bags are subjected to barometric pressure testing, undercover armed marshals travel on every flight and its planes are even equipped with anti-missile systems.

Elsewhere, better technology might improve the performance of conventional screening, but few airports can afford to update their systems whenever the latest gizmo comes out. Instead, says Mr Baum, they should use profiling to help make their procedures much less routine. “Airport security is far too predictable,” he adds, “Giving everyone a pat-down search is a waste of resources. Terrorists don’t like unpredictability.”

Mr Schneier is more dubious about profiling, and he is “incensed” by the way the TSA singles out some of the most unlikely passengers “for humiliation, abuse and sometimes theft”. He says that when people propose profiling, “they are really asking for a system that can apply judgment. Unfortunately that’s really hard. Rules are easier to explain and train…judgment requires better-educated, more expert and higher-paid screeners.”

Simply doing more of the kind of airport security by rote that is done now seems like a bad idea. There ought to be more emphasis on dealing with insider threats through better vetting and more intrusive monitoring of airside staff by CCTV. Apart from that, greater focus on passenger behaviour at the airport and less predictable forms of screening (for example, more swab tests, more use of sniffer dogs and so on) would be good.

But the most important thing of all might be to keep a sense of proportion. Many people travel on buses and trains, go to sporting events and attend open-air concerts. All are potential targets for terrorists, yet they receive not even a fraction of the attention that air travel gets.