And, since the TSA inspections are highly focussed towards the detection of firearms and explosives it would seem that anyone planning to harm an aircraft would realise this and choose another weapon or, at least, an alternative means of getting a weapon onto the aircraft. The vast majority of the detected firearms are the result of carelessness, stupid and culpable carelessness certainly and deserving of the relevant action certainly, but none the less, without evil intent. You can be assured that if the Federal authorities found a weapon that was genuinely intended to be used in a terrorist activity the event would be publicized to the skies. You would hear about it in headlines for a month - ergo the authorities also consider the 1400 detected firearms to be the result of culpable carelessness.
The TSA procedures are still more a pantomime for the travelling public than anything else. If you really wanted to board a weapon on a US aircraft you would use one of the thousands of immigrant airport workers from countries that dislike the US to smuggle the weapon to the aircraft via the thousands of serviceing and catering vehicles that enter the "back door" of the airports every hour.
Consider also that firearms in the US are the tools of sport as well as weapons., no different to many people here than golf clubs. There are thousands of weapons moving through US airports every day for sporting purposes and attendance at sporting events. There just is not the bed-wetting drama attached to a firearm that occurs in other countries. This is certainly not a justification for carelessness but it does facilitate errors. Simple example, a shooter travels from A to B, firearm is properly stowed in hold baggage. At hotel shooter removes firearm from suitcase and carries it to and from competition in a smaller range bag. End of competition, shooter packs secure gun container in suitcase and checks it but in the rush leaves actual gun in range bag which is carry-on, gotcha! Dumb, yes, evil, no, part of 1400 statistic, yes. 1.8 million people fly every day in the US, a few are going to make a mistake, apparently 4 per day.
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