It's no surprise that terrorists were once again targeting U.S. aviation. Since 9/11, airplanes and airports have remained at the very top of the potential hit list.
Analysts believe the al Qaeda's spectacular success on Sept. 11, 2001, made airplanes a kind of Holy Grail when it comes to targeting.
There is no question that U.S. aviation is significantly safer than it was five years ago: There are more air marshals, hardened cockpit doors, increased scrutiny (for explosives) of carry-on bags — and there is 100 percent screening of checked luggage. But vulnerabilities remain.
There is no system currently in place that lets screeners detect the component parts of a bomb. For example, a team of terrorists could carry common individual items (bleach, hair spray, cleaning agents, cell phones and radios) aboard a plane and assemble them into bombs while on board.
X-ray machines can find potential detonators, random "trace" swabs should be able to identify explosives in carry-on bags — if screeners are lucky enough to check the right bag — and "sniffers" (in a very few airports) are designed to find small bits of explosive residue on people.
But the system cannot detect unassembled bombs.
It is that very threat that has moved Homeland Security to raise the terror threat level.
Terrorists have been working on so-called liquid bombs since the mid-90s, when al Qaeda operative Ramzi Youssef accidentally set his apartment on fire in Manila. Youssef was working on the so-called Bojinka plot: Khalid Sheik Mohammad's plan to blow up airliners over the Pacific.
As a matter of routine business, it is not practical to ban all "liquid and gel" substances from carry-on bags. But out of an abundance of caution, that's what Homeland Security is doing.
This is leading to confusion and delays and airports. Security officials say all of that is necessary for now, until all of the details of the current plot are fully understood.
These measures are expected to be temporary. When the heat dies down, it is expected that the ban on liquids and gels will be relaxed.
But, the vulnerability will remain.