How to stop the next aircraft bomb

As Tuesday's tragedy in Belgium made clear, air travel remains vulnerable to determined terrorists. Three plotters, at least one of whom wore a suicide vest, killed or maimed hundreds by striking the unsecured front of the Brussels Airport, the departures terminal. The attack sparked an important debate about extending the security perimeter, as airports like Israel's Ben Gurion International and LAX have done to some degree.

But the check-in counter and the approaches to the airport aren't the only danger zones. For terrorist groups around the world, smuggling a bomb onto a plane is still the Holy Grail. And as recent attacks demonstrate, terrorists are learning to exploit back-of-the-airport employees like baggage handlers and catering and cleaning crews to bring down aircraft.

Twice in the last two months, the Shabab, an Al Qaeda affiliate, has turned its sights on passenger planes in Somalia. In February, one of the group's recruits blew himself out of an aircraft with a laptop bomb on a flight from Mogadishu to Djibouti; happily, the plane was able to land safely, and no one else was hurt. But the terrorists tried again March 7. When a luggage bomb went off prematurely at a checkpoint, it injured six. In both cases, reports suggest, the Shabab was counting on insiders to get its relatively unsophisticated explosives through security screenings.

The latest airline plots look very different from the pricey, sophisticated operation that brought down the World Trade Center on Sept. 11. Since then, the United States has made huge strides on aviation security. From the parking lot to the cockpit door, we hardened the targets that tempt terrorists. And despite some attempts — the shoe bomber and the underwear bomber, liquid bomb and cartridge bomb plots — no homeland flight has been taken down since 2001.

Islamic State's most important weapon isn't the assault rifle or the suicide vest — it's the man or woman on the inside, the sympathizer.

But in Africa and the Middle East, terrorists have learned how much damage low-cost, low-skill aviation plots can do. The proof of concept was Metrojet Flight 9268, which exploded over Sinai.

Last October, Islamic State's Egyptian branch affiliate managed to take down the Russian airliner, killing 224 passengers and crew, with the help of a man on the inside, a worker at Sharm el Sheik airport who got what the group claims was a bomb packed in a soda can onto the jet. The Shabab is now trying to copy this approach — smuggling explosives onto planes hidden in suitcases, laptops and other devices.

The insider threat, then, is the urgent risk in much of the world. By recruiting airport workers, whether they've been bribed or brainwashed, terrorist groups can take a shortcut around many security measures now in place. The rest is relatively easy. Simple bomb designs that can be hidden circulate widely online.

To adapt, airports in the developing world will need better equipment and deeper expertise. The United States can use both carrots and sticks to underline those priorities.

This work isn't glamorous. With the war against Islamic State raging in Iraq, Syria and now Libya, it's tempting to postpone these investments.

The power of the purse is a key tool. We need to set aside more funding to train and identify talented screeners, not just to secure U.S. airports, but also to work with trustworthy staff around the world. The State Department should use foreign aid and trade preferences to encourage best practices in aviation security, such as screening workers with access to airplanes. By investing in “partner capacity,” we make more flights secure — not just those with a leg in the U.S. — against our enemies' ambitions. These efforts protect Americans as well as foreigners who use non-U.S. carriers between foreign destinations.

But better security equipment and expertise in the developing world's airports can only achieve so much. We need better intelligence. Too few countries share information on known risks and trusted travelers; everyone wastes resources vetting the same passengers over and over, which allows some threats to slip through the cracks. We need to globalize “trusted traveler” programs, as the Department of Homeland Security has started to do with Germany, Mexico and South Korea. Pre-screening travelers can save time, resources and lives.

This work isn't glamorous. With the war against Islamic State raging in Iraq, Syria and now Libya, it's tempting to postpone these investments. Why spend a dollar on someone else's airport security when the same funds can go toward smart bombs, the CIA or arms for the Kurdish peshmerga? But the war on the ground is just a fraction of the fight. Every day Islamic State survives, radicals around the globe flock to its ideology, and many will turn their attention to the targets that have fixated terrorists for generations: jetliners.

Islamic State's most important weapon isn't the assault rifle or the suicide vest — it's the man or woman on the inside, the sympathizer. Answering this threat starts with stronger partnerships at airports around the world. After the February bombing, Somalia asked for the United States' help. Cleary, we haven't provided enough.

The opinions expressed here are solely those of the author.

This article was originally published in the Los Angeles Times.