A series of "systemic" failings in security and intelligence systems allowed alleged terrorist Umar Farouk Abdulmutallab to board the Christmas Day Northwest Flight 253 from Amsterdam to Detroit.
Here are some of the key criticisms that have emerged in the wake of the plot:
* Initial investigations into the failed attack found the information passed on by the father of Umar Farouk Abdulmutallab was not properly shared, meaning the 23-year-old was not barred from flying.
* The concerns of the suspect's father, expressed to US officials in Abdulmutallab's native Nigeria, were passed to the US authorities "weeks" before the alleged attack.
* Even without the father's warning, the US had enough material to have ensured Abdulmutallab would not have been free to fly.
US President Barack Obama said: "The warning signs would have triggered red flags and the suspect would have never been allowed to board that plane for America."
* Anti-terrorism intelligence systems put in place in the wake of the 9/11 attacks were not fully updated to take advantage of the information stored on it.
* "A mix of human and systemic failures that contributed to this potentially catastrophic breach of security", Mr Obama said.
* Abdulmutallab had been banned from entering Britain and placed on a "watch list" earlier this year.
* He was refused a new visa and was monitored by security services since last May after applying for a bogus college course.
* The suspect allegedly boarded the flight carrying explosives in his underpants, having passed through airport security.
* Abdulmutallab reportedly paid cash for his ticket in Ghana and did not carry any hold luggage for a two week trip to America - actions that would normally have aroused suspicion.