Officials: Only A Failed Detonator Saved Northwest Flight Screening machines may need to be replaced; Al Qaeda aware of 'Achilles heel.'

Dec. 26, 2009  -- Officials now say tragedy was only averted on Northwest flight 253 because a makeshift detonator failed to work properly.

Bomb experts say there was more than enough explosive to bring down the Northwest jet, which had nearly 300 people aboard, had the detonator not failed, and the nation's outdated airport screening machines may need to be upgraded.

"We've known for a long time that this is possible," said Richard Clarke, former counterterrorism czar and ABC News consultant, "and that we really have to replace our scanning devices with more modern systems."

Clarke said full body scans were needed, "but they're expensive and they're intrusive. They invade people's privacy."

Al Qaeda, said Clarke, is aware of this vulnerability in the U.S. airport security system. "They know that this is a weakness and an Achilles' heel in our airport security system and this is the second time they've tried it."

In 2001, would-be "shoe bomber" Richard Reid failed in his attempt to blow up a transatlantic flight with a highly explosive chemical known as PETN. He attempted to light a fuse to his shoe on a December 22 American Airlines flight from Paris to Miami but was subdued by other passengers.

According to investigators, the bomb on Northwest flight 253, which was en route from Amsterdam to Detroit when suspect Umar farouk Abdulmutallab allegedly detonated it, contained more than 80 grams of PETN. The material was allegedly sewn into Abdulmutallab's underwear, and was not detected by airport security.

READ THE CRIMINAL COMPLAINT AGAINST ABDULMUTALLAB HERE

The bomb was built and the plot organized, say U.S. officials, by al Qaeda leaders in Yemen, just north of the capital city of Sanaa.

Suspect Was On Terrorism Watch List

Authorities say the 23-year-old suspect spent months in Yemen being trained for the Christmas Day suicide mission.

Investigators believe Abdulmutallab was connected to al Qaeda by the same radical imam, American-born Anwar Awlaki, who is linked to the American Army major accused of opening fire at Fort Hood in November.

According to investigators, the bomb used yesterday was built in Yemen by a top al Qaeda bomb maker.

Northwest Airlines flight 253 -- operated on a Delta airplane - was getting ready to land in Detroit just before noon Friday when "a passenger caused a disturbance," said Delta spokeswoman Susan Chana Elliott. The man, later identified as Abdulmutallab, was trying to ignite when was initially reported as firecrackers.

According to the criminal complaint filed against Abudlmutallab, he boarded KLM Flight 588 from Lagos, Nigeria and transferred to Northwest Flight 253 at Schiphol Airport in Amsterdam.

Prior to the incident, Abdulmutallab went to the bathroom for about 20 minutes. Upon returning to his seat, Abdulmutallab said he had an upset stomach, and pulled a blanket over himself.

Passengers then heard popping noises similar to firecrackers and smelled an odor. Some saw Abdulmutallab's pants leg and the wall of the airplane on fire. Passengers and crew then subdued Abdulmutallab and used blankets and fire extinguishers to put out the flames.

A passenger apparently saw the suspect holding what a partially melted and smoking syringe. The passenger took the syringe, shook it to stop it from smoking and threw it to the floor. Dutch filmmaker Jasper Schuringa has been identified in the media as a passenger who subdued Mutallab.

Abdulmutallab, who flew from Nigeria to Amsterdam and then Detroit, was taken into custody at the Detroit airport and was interviewed by authorities there. He was then taken to an area hospital to be treated for burns.

Abdulmutallab was on a terrorism watch list, but not on a no-fly list. Said Clarke, "So once again, we have the U.S. government, as in the case of the Fort Hood attacks, knowing about someone, knowing that they were suspicious, but that information didn't get to the right people in time."

Matthew Cole, Joseph Rhee and Rhonda Schwartz contributed to this story