Published by the Wall Street Journal

The failed attempt to detonate an explosive device onboard Northwest Flight 253 is sparking new calls to rethink how authorities and airlines handle aviation security.

Reassessments also followed the terrorist attacks of Sept. 11, 2001, the abortive effort of “shoe bomber” Richard Reid to blow up an airliner in December 2001, and the discovery in the U.K. in 2006 of a plot to blow up jetliners using liquids smuggled onboard. Each event dramatically changed the screening of passengers, baggage and air cargo.

The latest incident is likely to focus attention on African airport security, as flights from the resource-rich continent increase amid instability and regional conflicts in many countries.

The recent attack, in which a Nigerian man traveling from Lagos through Amsterdam is alleged to have ignited an improvised bomb on a flight bound for Detroit, raises particularly difficult aviation-security issues.

The man, Umar Farouk Abdulmutallab, carried small amounts of powder and liquid on board the jetliner, according to officials. Aviation-security regulators have long known that small quantities of dangerous substances can elude even advanced screening, so they have set rules that tried to ensure terrorists couldn’t sneak enough on board to seriously damage an airplane.

Politicians and security experts now are urging governments to install more advanced scanning equipment, but also to emphasize in-person assessments of passengers, known as profiling. Several members of Congress, including Chairman of the Senate Homeland Security Committee Joseph Lieberman, on Sunday advocated wider use of new-technology full-body scanners.

Air-security experts caution that well-prepared attackers can still avoid detection. Drug traffickers routinely smuggle large quantities of narcotics inside their bodies and bomb components can be carried the same way. “There’s no silver-bullet technology, so we need to use behavioral analysis to select people for additional screening,” said Norman Shanks, an aviation-security consultant in England.

Such analysis looks at how people act, how they paid for their tickets — Mr. Abdulmutallab’s ticket was paid for in cash, often a red flag — and a variety of other factors.

People identified as unusual in some way are flagged for more-detailed physical screening. The U.S. Transport Security Administration — which is investing in a wide variety of new-technology scanning devices — has also expanded training of so-called Behavior Detection Officers to analyze passengers at airports and boarding planes.

Some critics say the approach isn’t sufficiently precise. Supporters say it has long been used effectively by law enforcement agents who size up passengers at the end of their journeys. “Customs and immigration officials find people doing illegal things getting off planes every day,” said Philip Baum, who runs Green Light Ltd., an aviation security training firm based in London. “There’s no reason we can’t find them as they get on.”

Mr. Abdulmutallab faced some questioning during the security check before boarding the Northwest flight in Amsterdam, as required by TSA rules. Investigators are now assessing how he was questioned and searched, according to the Dutch Justice Ministry.

Explosive material in Mr. Abdulmutallab’s cabin baggage could have escaped detection by the scanners through which all passengers must place carry-on items. Some advanced scanners can also detect explosives, but must be programmed for each different chemical compound.

If Mr. Abdulmutallab had the explosives attached to his body — or inside — and there was no metal, then few existing scanners would have picked them up. The full-body scanners advocated by the U.S. politicians might have identified objects concealed from view, however.

Schiphol, Amsterdam’s Airport, is now testing these machines, but only on a voluntary basis because the European Union hasn’t resolved privacy issues raised by the images, which essentially show a person naked.

It remains unclear whether Mr. Abdulmutallab carried the explosive materials with him from Nigeria or obtained them in Amsterdam. Still, Nigerian officials say they are reassessing their own airport security.

Nigeria has been battling to improve airline security and safety for several years. Security checks in Lagos now can be thorough and time-intensive. Lagos is among the few African airports served by several non-African carriers, prompting additional scrutiny by foreign authorities.

Dora Akunyili, Nigeria’s information minister, defended the airport security in Lagos. “If you say Lagos is corrupt, so is Amsterdam,” she said Sunday in an interview with The Wall Street Journal. “Our airport is not corrupt.”

Later, at a hastily called news conference, she said the international airport at Lagos had passed muster from the U.S. TSA this year. “However, in the light of the new developments, we have reinforced our security systems in all our airports,” she said. She offered no further details.

-Sarah Childress, Dough Cameron and Sudeep Reddy contributed to this article.

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