I really shouldn't open my mouth but way back at the beginning of the thread:
The aircraft is private property. Noone has the authority to enter it without your consent ...
The key word in this discussion is consent.
Avbug has not been saying that in all situations, LEOs have the right to search the aircraft, he has been saying that in some jurisdictions they do. The thread segued into reasonableness and probable cause but that was a mistake-- the doctrine at question is implied consent. In some jurisdictions, merely by virtue of landing at a [public use] airport you may have consented to a search of the aircraft. The onus is on the pilot/operator to know the regulations that pertain at each airport they visit. He's at least mostly right.
Implied consent gets applied often in DUI cases-- in many states you have consented to a breathalizer (a type of search) merely by operating a vehicle on public roads. This has been routinely upheld! In other cases such as search of a vehicle or apartment, the doctrine is sometimes upheld and sometimes denied by the courts. I am not aware of any case where it has been applied to an aircraft search, which may be part of the problem with this thread.
Often in legal cases where limited precedent exists, the question of the alleged infraction is measured against the actions of the 'reasonable person'* in the same situation. Pt 135 pilots being presumed professionals they would be held accountable to higher standard than a pt 91 owner/operator.
I think it's entirely reasonable to suppose in absence of cited precedent that:
In the case where flight goes from ABC to XYZ where XYZ does not permit firearms on airport property and there exists an implied consent law:
pt 91 pilot is let go
pt 135 pilot is charged and found guilty because the 135 would be expected to have known that he was flying into a location where his firearm was not permitted (absent other conditions such as federal deputizing, etc), since as a professional he is assumed to take greater care in his planning than an amateur (not a dig at professional 91 guys!)
In the case where the flight was intended from ABC to DFG but diverts to XYZ where DFG permits firearms, but XYZ does not:
both would be let go (but probably after long and costly legal proceedings), since the pilot did not expect to be at an airport where he could not posses the firearm.
The issue does not need to be as fracticous as firearm rights-- in the freight world we're moving to the point where some airports will have local regulations requiring anyone moving on the ramp to have high-visibility vests. I can not imagine that 'We didn't know [or attempt to find out].' would be an acceptable excuse from a commercial operator, though I imagine the transient GA aircraft pilots probably won't start racking up fines. Somewhere in the GOM for my company is a line which states that the most restrictive of FAR/GOM/state/local regulation is what we're required to adhere to. I can't imagine it's different with anyone else.
It's a fine thing to stand up for your rights, or even excersise civil disobedience if you think a law is unjust. Really! But I can't imagine any working pilot who can afford to fight a legal case like this just on principle, and if your job truely does require you to carry a firearm on your plane, and your job is worth having, then it's worth the time to check the local and state regulations of the places you fly through and get clearance from the sherrifs department or whatever to carry your gun while in the SIDA.
Not a lawyer, 121/125 pilot in any case, my opinion only, etc, etc,
-TF
*-http://en.wikipedia.org/wiki/Reasonable_person [I hate citing wiki, but whatever..]