Aviation security officials are investing in new technology to "sniff" out plastic explosives.
Aviation bomb plots keep the authorities at cutting edge
Aviation security officials have foiled several bomb plots in recent years by would-be attackers using explosive materials such as PETN (pentaerythritol tetranitrate).
In October two packages were found on separate cargo planes from Yemen and ultimately bound for the US. Each included several hundred grams of plastic explosives and a detonating mechanism. Although the bombs were designed to detonate in mid-air, they were discovered on the back of intelligence received from Saudi Arabia's security chief.
In December 2009, Umar Abdulmutallab, 25, a Nigerian national, attempted to detonate plastic explosives hidden in his underwear while on board a flight from Amsterdam to Detroit. Passengers subdued him after detecting a foul odour and flames climbing from his seat to the wall of the plane.
This "underwear bomber" was preceded by the 2002 "shoe bomber", the Briton Richard Reid, 38, who attempted to destroy a commercial aircraft in-flight by detonating explosives hidden in his shoes.
Both men were carrying only small amounts of explosives and that prompted authorities to invest in "explosives trace-detection portal machines" to detect explosives, and illegal drugs, at airports.
These "sniffing" machines are intended as a secondary screening device to support traditional X-ray machines.