Take the two Chechen women who brought down two Russian planes within minutes of each other. They used RDX, a detectable explosive, but smuggled it past lax Russian security. The Jihadists make common cause with the Chechens. They would no doubt share expertise.

Then we have Ramzi Yousef

who was involved in the 1993 World Trade Center bombing, concocted a plan a year later to attack 11 flights traveling from central Asia to the United States. The plot was uncovered in the Philippines in January 1995, two weeks before its execution date, after Yousef and others accidentally started a fire in their apartment and police showed up.

Before he was arrested, Yousef did a trial run with a lower-power bomb. He assembled it in the lavatory of a flight from Manila to Japan and left it on board after he departed on a connecting flight. The bomb exploded, but the Boeing 747 limped to an emergency landing with only one casualty.

Documents found on Yousef’s computer that emerged during his trial (Click here for PDF) showed that the plotters had filled bottles of contact lens solution with nitroglycerin and planned to use Casio digital watches as the timers, coupled with two 9-volt batteries in the bomb as a power source. The 9/11 Commission’s report said Yousef also had prepared dolls wearing clothes containing nitrocellulose, an explosive compound.

I’ve previously noted that Yousef may have had an indirect hand in the loss of TWA 800.

We know that the Jihadists have considerable expertise in using cell phones to trigger IED explosions. What would it take for them to smuggle a bomb in their checked luggage on board? Can they hermetically seal an RDX bomb so it can only be detected by X-rays? If they can do that then a passenger could trigger an explosive with a cell phone. But, why bother? Remember Pan Am flight 103?

It is hard to avoid the conclusion that terrorists could easily take down passenger jets. They’ve succeeded in the past. Why haven’t they tried more often? There are stable binary liquid explosives, such as Lixor, that they could smuggle aboard aircraft. Heck, all they have to do is infiltrate the crews who clean or maintain aircraft.

I tend towards the bigger bang theory. How do you top 9/11? Bombing a few planes wouldn’t be enough. All it would do is tighten airline security to the point where the terrorists themselves could not travel. The public would demand Muslim free air travel. Without relatively free air travel, terrorists could not attack Western targets.

So we see amateur efforts, such as the UK plot, that tie up resources and create public resentment at the authorities. But there is no concerted effort to bomb planes. The terrorist’s efforts are now directed towards bigger bangs.